diff options
| author | Linus Torvalds <torvalds@linux-foundation.org> | 2017-05-02 10:21:17 -0700 |
|---|---|---|
| committer | Linus Torvalds <torvalds@linux-foundation.org> | 2017-05-02 10:21:17 -0700 |
| commit | c58d4055c054fc6dc72f1be8bc71bd6fff209e48 (patch) | |
| tree | 56527e28fc65d74d6d5e8397c502ccc87a9ec99b /Documentation/usb | |
| parent | ceb198bb007b84ead867e87a71ffe715c4412b15 (diff) | |
| parent | 9bb0e9cb04c82d6bf0e72f3207307d621083b801 (diff) | |
| download | lwn-c58d4055c054fc6dc72f1be8bc71bd6fff209e48.tar.gz lwn-c58d4055c054fc6dc72f1be8bc71bd6fff209e48.zip | |
Merge tag 'docs-4.12' of git://git.lwn.net/linux
Pull documentation update from Jonathan Corbet:
"A reasonably busy cycle for documentation this time around. There is a
new guide for user-space API documents, rather sparsely populated at
the moment, but it's a start. Markus improved the infrastructure for
converting diagrams. Mauro has converted much of the USB documentation
over to RST. Plus the usual set of fixes, improvements, and tweaks.
There's a bit more than the usual amount of reaching out of
Documentation/ to fix comments elsewhere in the tree; I have acks for
those where I could get them"
* tag 'docs-4.12' of git://git.lwn.net/linux: (74 commits)
docs: Fix a couple typos
docs: Fix a spelling error in vfio-mediated-device.txt
docs: Fix a spelling error in ioctl-number.txt
MAINTAINERS: update file entry for HSI subsystem
Documentation: allow installing man pages to a user defined directory
Doc/PM: Sync with intel_powerclamp code behavior
zr364xx.rst: usb/devices is now at /sys/kernel/debug/
usb.rst: move documentation from proc_usb_info.txt to USB ReST book
convert philips.txt to ReST and add to media docs
docs-rst: usb: update old usbfs-related documentation
arm: Documentation: update a path name
docs: process/4.Coding.rst: Fix a couple of document refs
docs-rst: fix usb cross-references
usb: gadget.h: be consistent at kernel doc macros
usb: composite.h: fix two warnings when building docs
usb: get rid of some ReST doc build errors
usb.rst: get rid of some Sphinx errors
usb/URB.txt: convert to ReST and update it
usb/persist.txt: convert to ReST and add to driver-api book
usb/hotplug.txt: convert to ReST and add to driver-api book
...
Diffstat (limited to 'Documentation/usb')
| -rw-r--r-- | Documentation/usb/URB.txt | 261 | ||||
| -rw-r--r-- | Documentation/usb/acm.txt | 2 | ||||
| -rw-r--r-- | Documentation/usb/anchors.txt | 79 | ||||
| -rw-r--r-- | Documentation/usb/bulk-streams.txt | 78 | ||||
| -rw-r--r-- | Documentation/usb/callbacks.txt | 134 | ||||
| -rw-r--r-- | Documentation/usb/dma.txt | 133 | ||||
| -rw-r--r-- | Documentation/usb/error-codes.txt | 175 | ||||
| -rw-r--r-- | Documentation/usb/gadget_serial.txt | 4 | ||||
| -rw-r--r-- | Documentation/usb/hotplug.txt | 148 | ||||
| -rw-r--r-- | Documentation/usb/persist.txt | 165 | ||||
| -rw-r--r-- | Documentation/usb/power-management.txt | 772 | ||||
| -rw-r--r-- | Documentation/usb/proc_usb_info.txt | 390 |
12 files changed, 3 insertions, 2338 deletions
diff --git a/Documentation/usb/URB.txt b/Documentation/usb/URB.txt deleted file mode 100644 index 50da0d455444..000000000000 --- a/Documentation/usb/URB.txt +++ /dev/null @@ -1,261 +0,0 @@ -Revised: 2000-Dec-05. -Again: 2002-Jul-06 -Again: 2005-Sep-19 - - NOTE: - - The USB subsystem now has a substantial section in "The Linux Kernel API" - guide (in Documentation/DocBook), generated from the current source - code. This particular documentation file isn't particularly current or - complete; don't rely on it except for a quick overview. - - -1.1. Basic concept or 'What is an URB?' - -The basic idea of the new driver is message passing, the message itself is -called USB Request Block, or URB for short. - -- An URB consists of all relevant information to execute any USB transaction - and deliver the data and status back. - -- Execution of an URB is inherently an asynchronous operation, i.e. the - usb_submit_urb(urb) call returns immediately after it has successfully - queued the requested action. - -- Transfers for one URB can be canceled with usb_unlink_urb(urb) at any time. - -- Each URB has a completion handler, which is called after the action - has been successfully completed or canceled. The URB also contains a - context-pointer for passing information to the completion handler. - -- Each endpoint for a device logically supports a queue of requests. - You can fill that queue, so that the USB hardware can still transfer - data to an endpoint while your driver handles completion of another. - This maximizes use of USB bandwidth, and supports seamless streaming - of data to (or from) devices when using periodic transfer modes. - - -1.2. The URB structure - -Some of the fields in an URB are: - -struct urb -{ -// (IN) device and pipe specify the endpoint queue - struct usb_device *dev; // pointer to associated USB device - unsigned int pipe; // endpoint information - - unsigned int transfer_flags; // ISO_ASAP, SHORT_NOT_OK, etc. - -// (IN) all urbs need completion routines - void *context; // context for completion routine - void (*complete)(struct urb *); // pointer to completion routine - -// (OUT) status after each completion - int status; // returned status - -// (IN) buffer used for data transfers - void *transfer_buffer; // associated data buffer - int transfer_buffer_length; // data buffer length - int number_of_packets; // size of iso_frame_desc - -// (OUT) sometimes only part of CTRL/BULK/INTR transfer_buffer is used - int actual_length; // actual data buffer length - -// (IN) setup stage for CTRL (pass a struct usb_ctrlrequest) - unsigned char* setup_packet; // setup packet (control only) - -// Only for PERIODIC transfers (ISO, INTERRUPT) - // (IN/OUT) start_frame is set unless ISO_ASAP isn't set - int start_frame; // start frame - int interval; // polling interval - - // ISO only: packets are only "best effort"; each can have errors - int error_count; // number of errors - struct usb_iso_packet_descriptor iso_frame_desc[0]; -}; - -Your driver must create the "pipe" value using values from the appropriate -endpoint descriptor in an interface that it's claimed. - - -1.3. How to get an URB? - -URBs are allocated with the following call - - struct urb *usb_alloc_urb(int isoframes, int mem_flags) - -Return value is a pointer to the allocated URB, 0 if allocation failed. -The parameter isoframes specifies the number of isochronous transfer frames -you want to schedule. For CTRL/BULK/INT, use 0. The mem_flags parameter -holds standard memory allocation flags, letting you control (among other -things) whether the underlying code may block or not. - -To free an URB, use - - void usb_free_urb(struct urb *urb) - -You may free an urb that you've submitted, but which hasn't yet been -returned to you in a completion callback. It will automatically be -deallocated when it is no longer in use. - - -1.4. What has to be filled in? - -Depending on the type of transaction, there are some inline functions -defined in <linux/usb.h> to simplify the initialization, such as -fill_control_urb() and fill_bulk_urb(). In general, they need the usb -device pointer, the pipe (usual format from usb.h), the transfer buffer, -the desired transfer length, the completion handler, and its context. -Take a look at the some existing drivers to see how they're used. - -Flags: -For ISO there are two startup behaviors: Specified start_frame or ASAP. -For ASAP set URB_ISO_ASAP in transfer_flags. - -If short packets should NOT be tolerated, set URB_SHORT_NOT_OK in -transfer_flags. - - -1.5. How to submit an URB? - -Just call - - int usb_submit_urb(struct urb *urb, int mem_flags) - -The mem_flags parameter, such as SLAB_ATOMIC, controls memory allocation, -such as whether the lower levels may block when memory is tight. - -It immediately returns, either with status 0 (request queued) or some -error code, usually caused by the following: - -- Out of memory (-ENOMEM) -- Unplugged device (-ENODEV) -- Stalled endpoint (-EPIPE) -- Too many queued ISO transfers (-EAGAIN) -- Too many requested ISO frames (-EFBIG) -- Invalid INT interval (-EINVAL) -- More than one packet for INT (-EINVAL) - -After submission, urb->status is -EINPROGRESS; however, you should never -look at that value except in your completion callback. - -For isochronous endpoints, your completion handlers should (re)submit -URBs to the same endpoint with the ISO_ASAP flag, using multi-buffering, -to get seamless ISO streaming. - - -1.6. How to cancel an already running URB? - -There are two ways to cancel an URB you've submitted but which hasn't -been returned to your driver yet. For an asynchronous cancel, call - - int usb_unlink_urb(struct urb *urb) - -It removes the urb from the internal list and frees all allocated -HW descriptors. The status is changed to reflect unlinking. Note -that the URB will not normally have finished when usb_unlink_urb() -returns; you must still wait for the completion handler to be called. - -To cancel an URB synchronously, call - - void usb_kill_urb(struct urb *urb) - -It does everything usb_unlink_urb does, and in addition it waits -until after the URB has been returned and the completion handler -has finished. It also marks the URB as temporarily unusable, so -that if the completion handler or anyone else tries to resubmit it -they will get a -EPERM error. Thus you can be sure that when -usb_kill_urb() returns, the URB is totally idle. - -There is a lifetime issue to consider. An URB may complete at any -time, and the completion handler may free the URB. If this happens -while usb_unlink_urb or usb_kill_urb is running, it will cause a -memory-access violation. The driver is responsible for avoiding this, -which often means some sort of lock will be needed to prevent the URB -from being deallocated while it is still in use. - -On the other hand, since usb_unlink_urb may end up calling the -completion handler, the handler must not take any lock that is held -when usb_unlink_urb is invoked. The general solution to this problem -is to increment the URB's reference count while holding the lock, then -drop the lock and call usb_unlink_urb or usb_kill_urb, and then -decrement the URB's reference count. You increment the reference -count by calling - - struct urb *usb_get_urb(struct urb *urb) - -(ignore the return value; it is the same as the argument) and -decrement the reference count by calling usb_free_urb. Of course, -none of this is necessary if there's no danger of the URB being freed -by the completion handler. - - -1.7. What about the completion handler? - -The handler is of the following type: - - typedef void (*usb_complete_t)(struct urb *) - -I.e., it gets the URB that caused the completion call. In the completion -handler, you should have a look at urb->status to detect any USB errors. -Since the context parameter is included in the URB, you can pass -information to the completion handler. - -Note that even when an error (or unlink) is reported, data may have been -transferred. That's because USB transfers are packetized; it might take -sixteen packets to transfer your 1KByte buffer, and ten of them might -have transferred successfully before the completion was called. - - -NOTE: ***** WARNING ***** -NEVER SLEEP IN A COMPLETION HANDLER. These are often called in atomic -context. - -In the current kernel, completion handlers run with local interrupts -disabled, but in the future this will be changed, so don't assume that -local IRQs are always disabled inside completion handlers. - -1.8. How to do isochronous (ISO) transfers? - -For ISO transfers you have to fill a usb_iso_packet_descriptor structure, -allocated at the end of the URB by usb_alloc_urb(n,mem_flags), for each -packet you want to schedule. You also have to set urb->interval to say -how often to make transfers; it's often one per frame (which is once -every microframe for highspeed devices). The actual interval used will -be a power of two that's no bigger than what you specify. - -The usb_submit_urb() call modifies urb->interval to the implemented interval -value that is less than or equal to the requested interval value. If -ISO_ASAP scheduling is used, urb->start_frame is also updated. - -For each entry you have to specify the data offset for this frame (base is -transfer_buffer), and the length you want to write/expect to read. -After completion, actual_length contains the actual transferred length and -status contains the resulting status for the ISO transfer for this frame. -It is allowed to specify a varying length from frame to frame (e.g. for -audio synchronisation/adaptive transfer rates). You can also use the length -0 to omit one or more frames (striping). - -For scheduling you can choose your own start frame or ISO_ASAP. As explained -earlier, if you always keep at least one URB queued and your completion -keeps (re)submitting a later URB, you'll get smooth ISO streaming (if usb -bandwidth utilization allows). - -If you specify your own start frame, make sure it's several frames in advance -of the current frame. You might want this model if you're synchronizing -ISO data with some other event stream. - - -1.9. How to start interrupt (INT) transfers? - -Interrupt transfers, like isochronous transfers, are periodic, and happen -in intervals that are powers of two (1, 2, 4 etc) units. Units are frames -for full and low speed devices, and microframes for high speed ones. -The usb_submit_urb() call modifies urb->interval to the implemented interval -value that is less than or equal to the requested interval value. - -In Linux 2.6, unlike earlier versions, interrupt URBs are not automagically -restarted when they complete. They end when the completion handler is -called, just like other URBs. If you want an interrupt URB to be restarted, -your completion handler must resubmit it. diff --git a/Documentation/usb/acm.txt b/Documentation/usb/acm.txt index 17f5c2e1a570..903abca10517 100644 --- a/Documentation/usb/acm.txt +++ b/Documentation/usb/acm.txt @@ -64,7 +64,7 @@ minicom, ppp and mgetty with them. 2. Verifying that it works ~~~~~~~~~~~~~~~~~~~~~~~~~~ - The first step would be to check /proc/bus/usb/devices, it should look + The first step would be to check /sys/kernel/debug/usb/devices, it should look like this: T: Bus=01 Lev=00 Prnt=00 Port=00 Cnt=00 Dev#= 1 Spd=12 MxCh= 2 diff --git a/Documentation/usb/anchors.txt b/Documentation/usb/anchors.txt deleted file mode 100644 index fe6a99a32bbd..000000000000 --- a/Documentation/usb/anchors.txt +++ /dev/null @@ -1,79 +0,0 @@ -What is anchor? -=============== - -A USB driver needs to support some callbacks requiring -a driver to cease all IO to an interface. To do so, a -driver has to keep track of the URBs it has submitted -to know they've all completed or to call usb_kill_urb -for them. The anchor is a data structure takes care of -keeping track of URBs and provides methods to deal with -multiple URBs. - -Allocation and Initialisation -============================= - -There's no API to allocate an anchor. It is simply declared -as struct usb_anchor. init_usb_anchor() must be called to -initialise the data structure. - -Deallocation -============ - -Once it has no more URBs associated with it, the anchor can be -freed with normal memory management operations. - -Association and disassociation of URBs with anchors -=================================================== - -An association of URBs to an anchor is made by an explicit -call to usb_anchor_urb(). The association is maintained until -an URB is finished by (successful) completion. Thus disassociation -is automatic. A function is provided to forcibly finish (kill) -all URBs associated with an anchor. -Furthermore, disassociation can be made with usb_unanchor_urb() - -Operations on multitudes of URBs -================================ - -usb_kill_anchored_urbs() ------------------------- - -This function kills all URBs associated with an anchor. The URBs -are called in the reverse temporal order they were submitted. -This way no data can be reordered. - -usb_unlink_anchored_urbs() --------------------------- - -This function unlinks all URBs associated with an anchor. The URBs -are processed in the reverse temporal order they were submitted. -This is similar to usb_kill_anchored_urbs(), but it will not sleep. -Therefore no guarantee is made that the URBs have been unlinked when -the call returns. They may be unlinked later but will be unlinked in -finite time. - -usb_scuttle_anchored_urbs() ---------------------------- - -All URBs of an anchor are unanchored en masse. - -usb_wait_anchor_empty_timeout() -------------------------------- - -This function waits for all URBs associated with an anchor to finish -or a timeout, whichever comes first. Its return value will tell you -whether the timeout was reached. - -usb_anchor_empty() ------------------- - -Returns true if no URBs are associated with an anchor. Locking -is the caller's responsibility. - -usb_get_from_anchor() ---------------------- - -Returns the oldest anchored URB of an anchor. The URB is unanchored -and returned with a reference. As you may mix URBs to several -destinations in one anchor you have no guarantee the chronologically -first submitted URB is returned. diff --git a/Documentation/usb/bulk-streams.txt b/Documentation/usb/bulk-streams.txt deleted file mode 100644 index ffc02021863e..000000000000 --- a/Documentation/usb/bulk-streams.txt +++ /dev/null @@ -1,78 +0,0 @@ -Background -========== - -Bulk endpoint streams were added in the USB 3.0 specification. Streams allow a -device driver to overload a bulk endpoint so that multiple transfers can be -queued at once. - -Streams are defined in sections 4.4.6.4 and 8.12.1.4 of the Universal Serial Bus -3.0 specification at http://www.usb.org/developers/docs/ The USB Attached SCSI -Protocol, which uses streams to queue multiple SCSI commands, can be found on -the T10 website (http://t10.org/). - - -Device-side implications -======================== - -Once a buffer has been queued to a stream ring, the device is notified (through -an out-of-band mechanism on another endpoint) that data is ready for that stream -ID. The device then tells the host which "stream" it wants to start. The host -can also initiate a transfer on a stream without the device asking, but the -device can refuse that transfer. Devices can switch between streams at any -time. - - -Driver implications -=================== - -int usb_alloc_streams(struct usb_interface *interface, - struct usb_host_endpoint **eps, unsigned int num_eps, - unsigned int num_streams, gfp_t mem_flags); - -Device drivers will call this API to request that the host controller driver -allocate memory so the driver can use up to num_streams stream IDs. They must -pass an array of usb_host_endpoints that need to be setup with similar stream -IDs. This is to ensure that a UASP driver will be able to use the same stream -ID for the bulk IN and OUT endpoints used in a Bi-directional command sequence. - -The return value is an error condition (if one of the endpoints doesn't support -streams, or the xHCI driver ran out of memory), or the number of streams the -host controller allocated for this endpoint. The xHCI host controller hardware -declares how many stream IDs it can support, and each bulk endpoint on a -SuperSpeed device will say how many stream IDs it can handle. Therefore, -drivers should be able to deal with being allocated less stream IDs than they -requested. - -Do NOT call this function if you have URBs enqueued for any of the endpoints -passed in as arguments. Do not call this function to request less than two -streams. - -Drivers will only be allowed to call this API once for the same endpoint -without calling usb_free_streams(). This is a simplification for the xHCI host -controller driver, and may change in the future. - - -Picking new Stream IDs to use -============================ - -Stream ID 0 is reserved, and should not be used to communicate with devices. If -usb_alloc_streams() returns with a value of N, you may use streams 1 though N. -To queue an URB for a specific stream, set the urb->stream_id value. If the -endpoint does not support streams, an error will be returned. - -Note that new API to choose the next stream ID will have to be added if the xHCI -driver supports secondary stream IDs. - - -Clean up -======== - -If a driver wishes to stop using streams to communicate with the device, it -should call - -void usb_free_streams(struct usb_interface *interface, - struct usb_host_endpoint **eps, unsigned int num_eps, - gfp_t mem_flags); - -All stream IDs will be deallocated when the driver releases the interface, to -ensure that drivers that don't support streams will be able to use the endpoint. diff --git a/Documentation/usb/callbacks.txt b/Documentation/usb/callbacks.txt deleted file mode 100644 index 9e85846bdb98..000000000000 --- a/Documentation/usb/callbacks.txt +++ /dev/null @@ -1,134 +0,0 @@ -What callbacks will usbcore do? -=============================== - -Usbcore will call into a driver through callbacks defined in the driver -structure and through the completion handler of URBs a driver submits. -Only the former are in the scope of this document. These two kinds of -callbacks are completely independent of each other. Information on the -completion callback can be found in Documentation/usb/URB.txt. - -The callbacks defined in the driver structure are: - -1. Hotplugging callbacks: - - * @probe: Called to see if the driver is willing to manage a particular - * interface on a device. - * @disconnect: Called when the interface is no longer accessible, usually - * because its device has been (or is being) disconnected or the - * driver module is being unloaded. - -2. Odd backdoor through usbfs: - - * @ioctl: Used for drivers that want to talk to userspace through - * the "usbfs" filesystem. This lets devices provide ways to - * expose information to user space regardless of where they - * do (or don't) show up otherwise in the filesystem. - -3. Power management (PM) callbacks: - - * @suspend: Called when the device is going to be suspended. - * @resume: Called when the device is being resumed. - * @reset_resume: Called when the suspended device has been reset instead - * of being resumed. - -4. Device level operations: - - * @pre_reset: Called when the device is about to be reset. - * @post_reset: Called after the device has been reset - -The ioctl interface (2) should be used only if you have a very good -reason. Sysfs is preferred these days. The PM callbacks are covered -separately in Documentation/usb/power-management.txt. - -Calling conventions -=================== - -All callbacks are mutually exclusive. There's no need for locking -against other USB callbacks. All callbacks are called from a task -context. You may sleep. However, it is important that all sleeps have a -small fixed upper limit in time. In particular you must not call out to -user space and await results. - -Hotplugging callbacks -===================== - -These callbacks are intended to associate and disassociate a driver with -an interface. A driver's bond to an interface is exclusive. - -The probe() callback --------------------- - -int (*probe) (struct usb_interface *intf, - const struct usb_device_id *id); - -Accept or decline an interface. If you accept the device return 0, -otherwise -ENODEV or -ENXIO. Other error codes should be used only if a -genuine error occurred during initialisation which prevented a driver -from accepting a device that would else have been accepted. -You are strongly encouraged to use usbcore's facility, -usb_set_intfdata(), to associate a data structure with an interface, so -that you know which internal state and identity you associate with a -particular interface. The device will not be suspended and you may do IO -to the interface you are called for and endpoint 0 of the device. Device -initialisation that doesn't take too long is a good idea here. - -The disconnect() callback -------------------------- - -void (*disconnect) (struct usb_interface *intf); - -This callback is a signal to break any connection with an interface. -You are not allowed any IO to a device after returning from this -callback. You also may not do any other operation that may interfere -with another driver bound the interface, eg. a power management -operation. -If you are called due to a physical disconnection, all your URBs will be -killed by usbcore. Note that in this case disconnect will be called some -time after the physical disconnection. Thus your driver must be prepared -to deal with failing IO even prior to the callback. - -Device level callbacks -====================== - -pre_reset ---------- - -int (*pre_reset)(struct usb_interface *intf); - -A driver or user space is triggering a reset on the device which -contains the interface passed as an argument. Cease IO, wait for all -outstanding URBs to complete, and save any device state you need to -restore. No more URBs may be submitted until the post_reset method -is called. - -If you need to allocate memory here, use GFP_NOIO or GFP_ATOMIC, if you -are in atomic context. - -post_reset ----------- - -int (*post_reset)(struct usb_interface *intf); - -The reset has completed. Restore any saved device state and begin -using the device again. - -If you need to allocate memory here, use GFP_NOIO or GFP_ATOMIC, if you -are in atomic context. - -Call sequences -============== - -No callbacks other than probe will be invoked for an interface -that isn't bound to your driver. - -Probe will never be called for an interface bound to a driver. -Hence following a successful probe, disconnect will be called -before there is another probe for the same interface. - -Once your driver is bound to an interface, disconnect can be -called at any time except in between pre_reset and post_reset. -pre_reset is always followed by post_reset, even if the reset -failed or the device has been unplugged. - -suspend is always followed by one of: resume, reset_resume, or -disconnect. diff --git a/Documentation/usb/dma.txt b/Documentation/usb/dma.txt deleted file mode 100644 index 444651e70d95..000000000000 --- a/Documentation/usb/dma.txt +++ /dev/null @@ -1,133 +0,0 @@ -In Linux 2.5 kernels (and later), USB device drivers have additional control -over how DMA may be used to perform I/O operations. The APIs are detailed -in the kernel usb programming guide (kerneldoc, from the source code). - - -API OVERVIEW - -The big picture is that USB drivers can continue to ignore most DMA issues, -though they still must provide DMA-ready buffers (see -Documentation/DMA-API-HOWTO.txt). That's how they've worked through -the 2.4 (and earlier) kernels. - -OR: they can now be DMA-aware. - -- New calls enable DMA-aware drivers, letting them allocate dma buffers and - manage dma mappings for existing dma-ready buffers (see below). - -- URBs have an additional "transfer_dma" field, as well as a transfer_flags - bit saying if it's valid. (Control requests also have "setup_dma", but - drivers must not use it.) - -- "usbcore" will map this DMA address, if a DMA-aware driver didn't do - it first and set URB_NO_TRANSFER_DMA_MAP. HCDs - don't manage dma mappings for URBs. - -- There's a new "generic DMA API", parts of which are usable by USB device - drivers. Never use dma_set_mask() on any USB interface or device; that - would potentially break all devices sharing that bus. - - -ELIMINATING COPIES - -It's good to avoid making CPUs copy data needlessly. The costs can add up, -and effects like cache-trashing can impose subtle penalties. - -- If you're doing lots of small data transfers from the same buffer all - the time, that can really burn up resources on systems which use an - IOMMU to manage the DMA mappings. It can cost MUCH more to set up and - tear down the IOMMU mappings with each request than perform the I/O! - - For those specific cases, USB has primitives to allocate less expensive - memory. They work like kmalloc and kfree versions that give you the right - kind of addresses to store in urb->transfer_buffer and urb->transfer_dma. - You'd also set URB_NO_TRANSFER_DMA_MAP in urb->transfer_flags: - - void *usb_alloc_coherent (struct usb_device *dev, size_t size, - int mem_flags, dma_addr_t *dma); - - void usb_free_coherent (struct usb_device *dev, size_t size, - void *addr, dma_addr_t dma); - - Most drivers should *NOT* be using these primitives; they don't need - to use this type of memory ("dma-coherent"), and memory returned from - kmalloc() will work just fine. - - The memory buffer returned is "dma-coherent"; sometimes you might need to - force a consistent memory access ordering by using memory barriers. It's - not using a streaming DMA mapping, so it's good for small transfers on - systems where the I/O would otherwise thrash an IOMMU mapping. (See - Documentation/DMA-API-HOWTO.txt for definitions of "coherent" and - "streaming" DMA mappings.) - - Asking for 1/Nth of a page (as well as asking for N pages) is reasonably - space-efficient. - - On most systems the memory returned will be uncached, because the - semantics of dma-coherent memory require either bypassing CPU caches - or using cache hardware with bus-snooping support. While x86 hardware - has such bus-snooping, many other systems use software to flush cache - lines to prevent DMA conflicts. - -- Devices on some EHCI controllers could handle DMA to/from high memory. - - Unfortunately, the current Linux DMA infrastructure doesn't have a sane - way to expose these capabilities ... and in any case, HIGHMEM is mostly a - design wart specific to x86_32. So your best bet is to ensure you never - pass a highmem buffer into a USB driver. That's easy; it's the default - behavior. Just don't override it; e.g. with NETIF_F_HIGHDMA. - - This may force your callers to do some bounce buffering, copying from - high memory to "normal" DMA memory. If you can come up with a good way - to fix this issue (for x86_32 machines with over 1 GByte of memory), - feel free to submit patches. - - -WORKING WITH EXISTING BUFFERS - -Existing buffers aren't usable for DMA without first being mapped into the -DMA address space of the device. However, most buffers passed to your -driver can safely be used with such DMA mapping. (See the first section -of Documentation/DMA-API-HOWTO.txt, titled "What memory is DMA-able?") - -- When you're using scatterlists, you can map everything at once. On some - systems, this kicks in an IOMMU and turns the scatterlists into single - DMA transactions: - - int usb_buffer_map_sg (struct usb_device *dev, unsigned pipe, - struct scatterlist *sg, int nents); - - void usb_buffer_dmasync_sg (struct usb_device *dev, unsigned pipe, - struct scatterlist *sg, int n_hw_ents); - - void usb_buffer_unmap_sg (struct usb_device *dev, unsigned pipe, - struct scatterlist *sg, int n_hw_ents); - - It's probably easier to use the new usb_sg_*() calls, which do the DMA - mapping and apply other tweaks to make scatterlist i/o be fast. - -- Some drivers may prefer to work with the model that they're mapping large - buffers, synchronizing their safe re-use. (If there's no re-use, then let - usbcore do the map/unmap.) Large periodic transfers make good examples - here, since it's cheaper to just synchronize the buffer than to unmap it - each time an urb completes and then re-map it on during resubmission. - - These calls all work with initialized urbs: urb->dev, urb->pipe, - urb->transfer_buffer, and urb->transfer_buffer_length must all be - valid when these calls are used (urb->setup_packet must be valid too - if urb is a control request): - - struct urb *usb_buffer_map (struct urb *urb); - - void usb_buffer_dmasync (struct urb *urb); - - void usb_buffer_unmap (struct urb *urb); - - The calls manage urb->transfer_dma for you, and set URB_NO_TRANSFER_DMA_MAP - so that usbcore won't map or unmap the buffer. They cannot be used for - setup_packet buffers in control requests. - -Note that several of those interfaces are currently commented out, since -they don't have current users. See the source code. Other than the dmasync -calls (where the underlying DMA primitives have changed), most of them can -easily be commented back in if you want to use them. diff --git a/Documentation/usb/error-codes.txt b/Documentation/usb/error-codes.txt deleted file mode 100644 index 9c3eb845ebe5..000000000000 --- a/Documentation/usb/error-codes.txt +++ /dev/null @@ -1,175 +0,0 @@ -Revised: 2004-Oct-21 - -This is the documentation of (hopefully) all possible error codes (and -their interpretation) that can be returned from usbcore. - -Some of them are returned by the Host Controller Drivers (HCDs), which -device drivers only see through usbcore. As a rule, all the HCDs should -behave the same except for transfer speed dependent behaviors and the -way certain faults are reported. - - -************************************************************************** -* Error codes returned by usb_submit_urb * -************************************************************************** - -Non-USB-specific: - -0 URB submission went fine - --ENOMEM no memory for allocation of internal structures - -USB-specific: - --EBUSY The URB is already active. - --ENODEV specified USB-device or bus doesn't exist - --ENOENT specified interface or endpoint does not exist or - is not enabled - --ENXIO host controller driver does not support queuing of this type - of urb. (treat as a host controller bug.) - --EINVAL a) Invalid transfer type specified (or not supported) - b) Invalid or unsupported periodic transfer interval - c) ISO: attempted to change transfer interval - d) ISO: number_of_packets is < 0 - e) various other cases - --EXDEV ISO: URB_ISO_ASAP wasn't specified and all the frames - the URB would be scheduled in have already expired. - --EFBIG Host controller driver can't schedule that many ISO frames. - --EPIPE The pipe type specified in the URB doesn't match the - endpoint's actual type. - --EMSGSIZE (a) endpoint maxpacket size is zero; it is not usable - in the current interface altsetting. - (b) ISO packet is larger than the endpoint maxpacket. - (c) requested data transfer length is invalid: negative - or too large for the host controller. - --ENOSPC This request would overcommit the usb bandwidth reserved - for periodic transfers (interrupt, isochronous). - --ESHUTDOWN The device or host controller has been disabled due to some - problem that could not be worked around. - --EPERM Submission failed because urb->reject was set. - --EHOSTUNREACH URB was rejected because the device is suspended. - --ENOEXEC A control URB doesn't contain a Setup packet. - - -************************************************************************** -* Error codes returned by in urb->status * -* or in iso_frame_desc[n].status (for ISO) * -************************************************************************** - -USB device drivers may only test urb status values in completion handlers. -This is because otherwise there would be a race between HCDs updating -these values on one CPU, and device drivers testing them on another CPU. - -A transfer's actual_length may be positive even when an error has been -reported. That's because transfers often involve several packets, so that -one or more packets could finish before an error stops further endpoint I/O. - -For isochronous URBs, the urb status value is non-zero only if the URB is -unlinked, the device is removed, the host controller is disabled, or the total -transferred length is less than the requested length and the URB_SHORT_NOT_OK -flag is set. Completion handlers for isochronous URBs should only see -urb->status set to zero, -ENOENT, -ECONNRESET, -ESHUTDOWN, or -EREMOTEIO. -Individual frame descriptor status fields may report more status codes. - - -0 Transfer completed successfully - --ENOENT URB was synchronously unlinked by usb_unlink_urb - --EINPROGRESS URB still pending, no results yet - (That is, if drivers see this it's a bug.) - --EPROTO (*, **) a) bitstuff error - b) no response packet received within the - prescribed bus turn-around time - c) unknown USB error - --EILSEQ (*, **) a) CRC mismatch - b) no response packet received within the - prescribed bus turn-around time - c) unknown USB error - - Note that often the controller hardware does not - distinguish among cases a), b), and c), so a - driver cannot tell whether there was a protocol - error, a failure to respond (often caused by - device disconnect), or some other fault. - --ETIME (**) No response packet received within the prescribed - bus turn-around time. This error may instead be - reported as -EPROTO or -EILSEQ. - --ETIMEDOUT Synchronous USB message functions use this code - to indicate timeout expired before the transfer - completed, and no other error was reported by HC. - --EPIPE (**) Endpoint stalled. For non-control endpoints, - reset this status with usb_clear_halt(). - --ECOMM During an IN transfer, the host controller - received data from an endpoint faster than it - could be written to system memory - --ENOSR During an OUT transfer, the host controller - could not retrieve data from system memory fast - enough to keep up with the USB data rate - --EOVERFLOW (*) The amount of data returned by the endpoint was - greater than either the max packet size of the - endpoint or the remaining buffer size. "Babble". - --EREMOTEIO The data read from the endpoint did not fill the - specified buffer, and URB_SHORT_NOT_OK was set in - urb->transfer_flags. - --ENODEV Device was removed. Often preceded by a burst of - other errors, since the hub driver doesn't detect - device removal events immediately. - --EXDEV ISO transfer only partially completed - (only set in iso_frame_desc[n].status, not urb->status) - --EINVAL ISO madness, if this happens: Log off and go home - --ECONNRESET URB was asynchronously unlinked by usb_unlink_urb - --ESHUTDOWN The device or host controller has been disabled due - to some problem that could not be worked around, - such as a physical disconnect. - - -(*) Error codes like -EPROTO, -EILSEQ and -EOVERFLOW normally indicate -hardware problems such as bad devices (including firmware) or cables. - -(**) This is also one of several codes that different kinds of host -controller use to indicate a transfer has failed because of device -disconnect. In the interval before the hub driver starts disconnect -processing, devices may receive such fault reports for every request. - - - -************************************************************************** -* Error codes returned by usbcore-functions * -* (expect also other submit and transfer status codes) * -************************************************************************** - -usb_register(): --EINVAL error during registering new driver - -usb_get_*/usb_set_*(): -usb_control_msg(): -usb_bulk_msg(): --ETIMEDOUT Timeout expired before the transfer completed. diff --git a/Documentation/usb/gadget_serial.txt b/Documentation/usb/gadget_serial.txt index 6b4a88a8c8e3..d1def3186782 100644 --- a/Documentation/usb/gadget_serial.txt +++ b/Documentation/usb/gadget_serial.txt @@ -189,7 +189,7 @@ Once the gadget serial driver is loaded and the USB device connected to the Linux host with a USB cable, the host system should recognize the gadget serial device. For example, the command - cat /proc/bus/usb/devices + cat /sys/kernel/debug/usb/devices should show something like this: @@ -221,7 +221,7 @@ Once the gadget serial driver is loaded and the USB device connected to the Linux host with a USB cable, the host system should recognize the gadget serial device. For example, the command - cat /proc/bus/usb/devices + cat /sys/kernel/debug/usb/devices should show something like this: diff --git a/Documentation/usb/hotplug.txt b/Documentation/usb/hotplug.txt deleted file mode 100644 index 5b243f315b2c..000000000000 --- a/Documentation/usb/hotplug.txt +++ /dev/null @@ -1,148 +0,0 @@ -LINUX HOTPLUGGING - -In hotpluggable busses like USB (and Cardbus PCI), end-users plug devices -into the bus with power on. In most cases, users expect the devices to become -immediately usable. That means the system must do many things, including: - - - Find a driver that can handle the device. That may involve - loading a kernel module; newer drivers can use module-init-tools - to publish their device (and class) support to user utilities. - - - Bind a driver to that device. Bus frameworks do that using a - device driver's probe() routine. - - - Tell other subsystems to configure the new device. Print - queues may need to be enabled, networks brought up, disk - partitions mounted, and so on. In some cases these will - be driver-specific actions. - -This involves a mix of kernel mode and user mode actions. Making devices -be immediately usable means that any user mode actions can't wait for an -administrator to do them: the kernel must trigger them, either passively -(triggering some monitoring daemon to invoke a helper program) or -actively (calling such a user mode helper program directly). - -Those triggered actions must support a system's administrative policies; -such programs are called "policy agents" here. Typically they involve -shell scripts that dispatch to more familiar administration tools. - -Because some of those actions rely on information about drivers (metadata) -that is currently available only when the drivers are dynamically linked, -you get the best hotplugging when you configure a highly modular system. - - -KERNEL HOTPLUG HELPER (/sbin/hotplug) - -There is a kernel parameter: /proc/sys/kernel/hotplug, which normally -holds the pathname "/sbin/hotplug". That parameter names a program -which the kernel may invoke at various times. - -The /sbin/hotplug program can be invoked by any subsystem as part of its -reaction to a configuration change, from a thread in that subsystem. -Only one parameter is required: the name of a subsystem being notified of -some kernel event. That name is used as the first key for further event -dispatch; any other argument and environment parameters are specified by -the subsystem making that invocation. - -Hotplug software and other resources is available at: - - http://linux-hotplug.sourceforge.net - -Mailing list information is also available at that site. - - --------------------------------------------------------------------------- - - -USB POLICY AGENT - -The USB subsystem currently invokes /sbin/hotplug when USB devices -are added or removed from system. The invocation is done by the kernel -hub workqueue [hub_wq], or else as part of root hub initialization -(done by init, modprobe, kapmd, etc). Its single command line parameter -is the string "usb", and it passes these environment variables: - - ACTION ... "add", "remove" - PRODUCT ... USB vendor, product, and version codes (hex) - TYPE ... device class codes (decimal) - INTERFACE ... interface 0 class codes (decimal) - -If "usbdevfs" is configured, DEVICE and DEVFS are also passed. DEVICE is -the pathname of the device, and is useful for devices with multiple and/or -alternate interfaces that complicate driver selection. By design, USB -hotplugging is independent of "usbdevfs": you can do most essential parts -of USB device setup without using that filesystem, and without running a -user mode daemon to detect changes in system configuration. - -Currently available policy agent implementations can load drivers for -modules, and can invoke driver-specific setup scripts. The newest ones -leverage USB module-init-tools support. Later agents might unload drivers. - - -USB MODUTILS SUPPORT - -Current versions of module-init-tools will create a "modules.usbmap" file -which contains the entries from each driver's MODULE_DEVICE_TABLE. Such -files can be used by various user mode policy agents to make sure all the -right driver modules get loaded, either at boot time or later. - -See <linux/usb.h> for full information about such table entries; or look -at existing drivers. Each table entry describes one or more criteria to -be used when matching a driver to a device or class of devices. The -specific criteria are identified by bits set in "match_flags", paired -with field values. You can construct the criteria directly, or with -macros such as these, and use driver_info to store more information. - - USB_DEVICE (vendorId, productId) - ... matching devices with specified vendor and product ids - USB_DEVICE_VER (vendorId, productId, lo, hi) - ... like USB_DEVICE with lo <= productversion <= hi - USB_INTERFACE_INFO (class, subclass, protocol) - ... matching specified interface class info - USB_DEVICE_INFO (class, subclass, protocol) - ... matching specified device class info - -A short example, for a driver that supports several specific USB devices -and their quirks, might have a MODULE_DEVICE_TABLE like this: - - static const struct usb_device_id mydriver_id_table[] = { - { USB_DEVICE (0x9999, 0xaaaa), driver_info: QUIRK_X }, - { USB_DEVICE (0xbbbb, 0x8888), driver_info: QUIRK_Y|QUIRK_Z }, - ... - { } /* end with an all-zeroes entry */ - }; - MODULE_DEVICE_TABLE(usb, mydriver_id_table); - -Most USB device drivers should pass these tables to the USB subsystem as -well as to the module management subsystem. Not all, though: some driver -frameworks connect using interfaces layered over USB, and so they won't -need such a "struct usb_driver". - -Drivers that connect directly to the USB subsystem should be declared -something like this: - - static struct usb_driver mydriver = { - .name = "mydriver", - .id_table = mydriver_id_table, - .probe = my_probe, - .disconnect = my_disconnect, - - /* - if using the usb chardev framework: - .minor = MY_USB_MINOR_START, - .fops = my_file_ops, - if exposing any operations through usbdevfs: - .ioctl = my_ioctl, - */ - }; - -When the USB subsystem knows about a driver's device ID table, it's used when -choosing drivers to probe(). The thread doing new device processing checks -drivers' device ID entries from the MODULE_DEVICE_TABLE against interface and -device descriptors for the device. It will only call probe() if there is a -match, and the third argument to probe() will be the entry that matched. - -If you don't provide an id_table for your driver, then your driver may get -probed for each new device; the third parameter to probe() will be null. - - diff --git a/Documentation/usb/persist.txt b/Documentation/usb/persist.txt deleted file mode 100644 index 35d70eda9ad6..000000000000 --- a/Documentation/usb/persist.txt +++ /dev/null @@ -1,165 +0,0 @@ - USB device persistence during system suspend - - Alan Stern <stern@rowland.harvard.edu> - - September 2, 2006 (Updated February 25, 2008) - - - What is the problem? - -According to the USB specification, when a USB bus is suspended the -bus must continue to supply suspend current (around 1-5 mA). This -is so that devices can maintain their internal state and hubs can -detect connect-change events (devices being plugged in or unplugged). -The technical term is "power session". - -If a USB device's power session is interrupted then the system is -required to behave as though the device has been unplugged. It's a -conservative approach; in the absence of suspend current the computer -has no way to know what has actually happened. Perhaps the same -device is still attached or perhaps it was removed and a different -device plugged into the port. The system must assume the worst. - -By default, Linux behaves according to the spec. If a USB host -controller loses power during a system suspend, then when the system -wakes up all the devices attached to that controller are treated as -though they had disconnected. This is always safe and it is the -"officially correct" thing to do. - -For many sorts of devices this behavior doesn't matter in the least. -If the kernel wants to believe that your USB keyboard was unplugged -while the system was asleep and a new keyboard was plugged in when the -system woke up, who cares? It'll still work the same when you type on -it. - -Unfortunately problems _can_ arise, particularly with mass-storage -devices. The effect is exactly the same as if the device really had -been unplugged while the system was suspended. If you had a mounted -filesystem on the device, you're out of luck -- everything in that -filesystem is now inaccessible. This is especially annoying if your -root filesystem was located on the device, since your system will -instantly crash. - -Loss of power isn't the only mechanism to worry about. Anything that -interrupts a power session will have the same effect. For example, -even though suspend current may have been maintained while the system -was asleep, on many systems during the initial stages of wakeup the -firmware (i.e., the BIOS) resets the motherboard's USB host -controllers. Result: all the power sessions are destroyed and again -it's as though you had unplugged all the USB devices. Yes, it's -entirely the BIOS's fault, but that doesn't do _you_ any good unless -you can convince the BIOS supplier to fix the problem (lots of luck!). - -On many systems the USB host controllers will get reset after a -suspend-to-RAM. On almost all systems, no suspend current is -available during hibernation (also known as swsusp or suspend-to-disk). -You can check the kernel log after resuming to see if either of these -has happened; look for lines saying "root hub lost power or was reset". - -In practice, people are forced to unmount any filesystems on a USB -device before suspending. If the root filesystem is on a USB device, -the system can't be suspended at all. (All right, it _can_ be -suspended -- but it will crash as soon as it wakes up, which isn't -much better.) - - - What is the solution? - -The kernel includes a feature called USB-persist. It tries to work -around these issues by allowing the core USB device data structures to -persist across a power-session disruption. - -It works like this. If the kernel sees that a USB host controller is -not in the expected state during resume (i.e., if the controller was -reset or otherwise had lost power) then it applies a persistence check -to each of the USB devices below that controller for which the -"persist" attribute is set. It doesn't try to resume the device; that -can't work once the power session is gone. Instead it issues a USB -port reset and then re-enumerates the device. (This is exactly the -same thing that happens whenever a USB device is reset.) If the -re-enumeration shows that the device now attached to that port has the -same descriptors as before, including the Vendor and Product IDs, then -the kernel continues to use the same device structure. In effect, the -kernel treats the device as though it had merely been reset instead of -unplugged. - -The same thing happens if the host controller is in the expected state -but a USB device was unplugged and then replugged, or if a USB device -fails to carry out a normal resume. - -If no device is now attached to the port, or if the descriptors are -different from what the kernel remembers, then the treatment is what -you would expect. The kernel destroys the old device structure and -behaves as though the old device had been unplugged and a new device -plugged in. - -The end result is that the USB device remains available and usable. -Filesystem mounts and memory mappings are unaffected, and the world is -now a good and happy place. - -Note that the "USB-persist" feature will be applied only to those -devices for which it is enabled. You can enable the feature by doing -(as root): - - echo 1 >/sys/bus/usb/devices/.../power/persist - -where the "..." should be filled in the with the device's ID. Disable -the feature by writing 0 instead of 1. For hubs the feature is -automatically and permanently enabled and the power/persist file -doesn't even exist, so you only have to worry about setting it for -devices where it really matters. - - - Is this the best solution? - -Perhaps not. Arguably, keeping track of mounted filesystems and -memory mappings across device disconnects should be handled by a -centralized Logical Volume Manager. Such a solution would allow you -to plug in a USB flash device, create a persistent volume associated -with it, unplug the flash device, plug it back in later, and still -have the same persistent volume associated with the device. As such -it would be more far-reaching than USB-persist. - -On the other hand, writing a persistent volume manager would be a big -job and using it would require significant input from the user. This -solution is much quicker and easier -- and it exists now, a giant -point in its favor! - -Furthermore, the USB-persist feature applies to _all_ USB devices, not -just mass-storage devices. It might turn out to be equally useful for -other device types, such as network interfaces. - - - WARNING: USB-persist can be dangerous!! - -When recovering an interrupted power session the kernel does its best -to make sure the USB device hasn't been changed; that is, the same -device is still plugged into the port as before. But the checks -aren't guaranteed to be 100% accurate. - -If you replace one USB device with another of the same type (same -manufacturer, same IDs, and so on) there's an excellent chance the -kernel won't detect the change. The serial number string and other -descriptors are compared with the kernel's stored values, but this -might not help since manufacturers frequently omit serial numbers -entirely in their devices. - -Furthermore it's quite possible to leave a USB device exactly the same -while changing its media. If you replace the flash memory card in a -USB card reader while the system is asleep, the kernel will have no -way to know you did it. The kernel will assume that nothing has -happened and will continue to use the partition tables, inodes, and -memory mappings for the old card. - -If the kernel gets fooled in this way, it's almost certain to cause -data corruption and to crash your system. You'll have no one to blame -but yourself. - -For those devices with avoid_reset_quirk attribute being set, persist -maybe fail because they may morph after reset. - -YOU HAVE BEEN WARNED! USE AT YOUR OWN RISK! - -That having been said, most of the time there shouldn't be any trouble -at all. The USB-persist feature can be extremely useful. Make the -most of it. diff --git a/Documentation/usb/power-management.txt b/Documentation/usb/power-management.txt deleted file mode 100644 index 00e706997130..000000000000 --- a/Documentation/usb/power-management.txt +++ /dev/null @@ -1,772 +0,0 @@ - Power Management for USB - - Alan Stern <stern@rowland.harvard.edu> - - Last-updated: February 2014 - - - Contents: - --------- - * What is Power Management? - * What is Remote Wakeup? - * When is a USB device idle? - * Forms of dynamic PM - * The user interface for dynamic PM - * Changing the default idle-delay time - * Warnings - * The driver interface for Power Management - * The driver interface for autosuspend and autoresume - * Other parts of the driver interface - * Mutual exclusion - * Interaction between dynamic PM and system PM - * xHCI hardware link PM - * USB Port Power Control - * User Interface for Port Power Control - * Suggested Userspace Port Power Policy - - - What is Power Management? - ------------------------- - -Power Management (PM) is the practice of saving energy by suspending -parts of a computer system when they aren't being used. While a -component is "suspended" it is in a nonfunctional low-power state; it -might even be turned off completely. A suspended component can be -"resumed" (returned to a functional full-power state) when the kernel -needs to use it. (There also are forms of PM in which components are -placed in a less functional but still usable state instead of being -suspended; an example would be reducing the CPU's clock rate. This -document will not discuss those other forms.) - -When the parts being suspended include the CPU and most of the rest of -the system, we speak of it as a "system suspend". When a particular -device is turned off while the system as a whole remains running, we -call it a "dynamic suspend" (also known as a "runtime suspend" or -"selective suspend"). This document concentrates mostly on how -dynamic PM is implemented in the USB subsystem, although system PM is -covered to some extent (see Documentation/power/*.txt for more -information about system PM). - -System PM support is present only if the kernel was built with CONFIG_SUSPEND -or CONFIG_HIBERNATION enabled. Dynamic PM support for USB is present whenever -the kernel was built with CONFIG_PM enabled. - -[Historically, dynamic PM support for USB was present only if the -kernel had been built with CONFIG_USB_SUSPEND enabled (which depended on -CONFIG_PM_RUNTIME). Starting with the 3.10 kernel release, dynamic PM support -for USB was present whenever the kernel was built with CONFIG_PM_RUNTIME -enabled. The CONFIG_USB_SUSPEND option had been eliminated.] - - - What is Remote Wakeup? - ---------------------- - -When a device has been suspended, it generally doesn't resume until -the computer tells it to. Likewise, if the entire computer has been -suspended, it generally doesn't resume until the user tells it to, say -by pressing a power button or opening the cover. - -However some devices have the capability of resuming by themselves, or -asking the kernel to resume them, or even telling the entire computer -to resume. This capability goes by several names such as "Wake On -LAN"; we will refer to it generically as "remote wakeup". When a -device is enabled for remote wakeup and it is suspended, it may resume -itself (or send a request to be resumed) in response to some external -event. Examples include a suspended keyboard resuming when a key is -pressed, or a suspended USB hub resuming when a device is plugged in. - - - When is a USB device idle? - -------------------------- - -A device is idle whenever the kernel thinks it's not busy doing -anything important and thus is a candidate for being suspended. The -exact definition depends on the device's driver; drivers are allowed -to declare that a device isn't idle even when there's no actual -communication taking place. (For example, a hub isn't considered idle -unless all the devices plugged into that hub are already suspended.) -In addition, a device isn't considered idle so long as a program keeps -its usbfs file open, whether or not any I/O is going on. - -If a USB device has no driver, its usbfs file isn't open, and it isn't -being accessed through sysfs, then it definitely is idle. - - - Forms of dynamic PM - ------------------- - -Dynamic suspends occur when the kernel decides to suspend an idle -device. This is called "autosuspend" for short. In general, a device -won't be autosuspended unless it has been idle for some minimum period -of time, the so-called idle-delay time. - -Of course, nothing the kernel does on its own initiative should -prevent the computer or its devices from working properly. If a -device has been autosuspended and a program tries to use it, the -kernel will automatically resume the device (autoresume). For the -same reason, an autosuspended device will usually have remote wakeup -enabled, if the device supports remote wakeup. - -It is worth mentioning that many USB drivers don't support -autosuspend. In fact, at the time of this writing (Linux 2.6.23) the -only drivers which do support it are the hub driver, kaweth, asix, -usblp, usblcd, and usb-skeleton (which doesn't count). If a -non-supporting driver is bound to a device, the device won't be -autosuspended. In effect, the kernel pretends the device is never -idle. - -We can categorize power management events in two broad classes: -external and internal. External events are those triggered by some -agent outside the USB stack: system suspend/resume (triggered by -userspace), manual dynamic resume (also triggered by userspace), and -remote wakeup (triggered by the device). Internal events are those -triggered within the USB stack: autosuspend and autoresume. Note that -all dynamic suspend events are internal; external agents are not -allowed to issue dynamic suspends. - - - The user interface for dynamic PM - --------------------------------- - -The user interface for controlling dynamic PM is located in the power/ -subdirectory of each USB device's sysfs directory, that is, in -/sys/bus/usb/devices/.../power/ where "..." is the device's ID. The -relevant attribute files are: wakeup, control, and -autosuspend_delay_ms. (There may also be a file named "level"; this -file was deprecated as of the 2.6.35 kernel and replaced by the -"control" file. In 2.6.38 the "autosuspend" file will be deprecated -and replaced by the "autosuspend_delay_ms" file. The only difference -is that the newer file expresses the delay in milliseconds whereas the -older file uses seconds. Confusingly, both files are present in 2.6.37 -but only "autosuspend" works.) - - power/wakeup - - This file is empty if the device does not support - remote wakeup. Otherwise the file contains either the - word "enabled" or the word "disabled", and you can - write those words to the file. The setting determines - whether or not remote wakeup will be enabled when the - device is next suspended. (If the setting is changed - while the device is suspended, the change won't take - effect until the following suspend.) - - power/control - - This file contains one of two words: "on" or "auto". - You can write those words to the file to change the - device's setting. - - "on" means that the device should be resumed and - autosuspend is not allowed. (Of course, system - suspends are still allowed.) - - "auto" is the normal state in which the kernel is - allowed to autosuspend and autoresume the device. - - (In kernels up to 2.6.32, you could also specify - "suspend", meaning that the device should remain - suspended and autoresume was not allowed. This - setting is no longer supported.) - - power/autosuspend_delay_ms - - This file contains an integer value, which is the - number of milliseconds the device should remain idle - before the kernel will autosuspend it (the idle-delay - time). The default is 2000. 0 means to autosuspend - as soon as the device becomes idle, and negative - values mean never to autosuspend. You can write a - number to the file to change the autosuspend - idle-delay time. - -Writing "-1" to power/autosuspend_delay_ms and writing "on" to -power/control do essentially the same thing -- they both prevent the -device from being autosuspended. Yes, this is a redundancy in the -API. - -(In 2.6.21 writing "0" to power/autosuspend would prevent the device -from being autosuspended; the behavior was changed in 2.6.22. The -power/autosuspend attribute did not exist prior to 2.6.21, and the -power/level attribute did not exist prior to 2.6.22. power/control -was added in 2.6.34, and power/autosuspend_delay_ms was added in -2.6.37 but did not become functional until 2.6.38.) - - - Changing the default idle-delay time - ------------------------------------ - -The default autosuspend idle-delay time (in seconds) is controlled by -a module parameter in usbcore. You can specify the value when usbcore -is loaded. For example, to set it to 5 seconds instead of 2 you would -do: - - modprobe usbcore autosuspend=5 - -Equivalently, you could add to a configuration file in /etc/modprobe.d -a line saying: - - options usbcore autosuspend=5 - -Some distributions load the usbcore module very early during the boot -process, by means of a program or script running from an initramfs -image. To alter the parameter value you would have to rebuild that -image. - -If usbcore is compiled into the kernel rather than built as a loadable -module, you can add - - usbcore.autosuspend=5 - -to the kernel's boot command line. - -Finally, the parameter value can be changed while the system is -running. If you do: - - echo 5 >/sys/module/usbcore/parameters/autosuspend - -then each new USB device will have its autosuspend idle-delay -initialized to 5. (The idle-delay values for already existing devices -will not be affected.) - -Setting the initial default idle-delay to -1 will prevent any -autosuspend of any USB device. This has the benefit of allowing you -then to enable autosuspend for selected devices. - - - Warnings - -------- - -The USB specification states that all USB devices must support power -management. Nevertheless, the sad fact is that many devices do not -support it very well. You can suspend them all right, but when you -try to resume them they disconnect themselves from the USB bus or -they stop working entirely. This seems to be especially prevalent -among printers and scanners, but plenty of other types of device have -the same deficiency. - -For this reason, by default the kernel disables autosuspend (the -power/control attribute is initialized to "on") for all devices other -than hubs. Hubs, at least, appear to be reasonably well-behaved in -this regard. - -(In 2.6.21 and 2.6.22 this wasn't the case. Autosuspend was enabled -by default for almost all USB devices. A number of people experienced -problems as a result.) - -This means that non-hub devices won't be autosuspended unless the user -or a program explicitly enables it. As of this writing there aren't -any widespread programs which will do this; we hope that in the near -future device managers such as HAL will take on this added -responsibility. In the meantime you can always carry out the -necessary operations by hand or add them to a udev script. You can -also change the idle-delay time; 2 seconds is not the best choice for -every device. - -If a driver knows that its device has proper suspend/resume support, -it can enable autosuspend all by itself. For example, the video -driver for a laptop's webcam might do this (in recent kernels they -do), since these devices are rarely used and so should normally be -autosuspended. - -Sometimes it turns out that even when a device does work okay with -autosuspend there are still problems. For example, the usbhid driver, -which manages keyboards and mice, has autosuspend support. Tests with -a number of keyboards show that typing on a suspended keyboard, while -causing the keyboard to do a remote wakeup all right, will nonetheless -frequently result in lost keystrokes. Tests with mice show that some -of them will issue a remote-wakeup request in response to button -presses but not to motion, and some in response to neither. - -The kernel will not prevent you from enabling autosuspend on devices -that can't handle it. It is even possible in theory to damage a -device by suspending it at the wrong time. (Highly unlikely, but -possible.) Take care. - - - The driver interface for Power Management - ----------------------------------------- - -The requirements for a USB driver to support external power management -are pretty modest; the driver need only define - - .suspend - .resume - .reset_resume - -methods in its usb_driver structure, and the reset_resume method is -optional. The methods' jobs are quite simple: - - The suspend method is called to warn the driver that the - device is going to be suspended. If the driver returns a - negative error code, the suspend will be aborted. Normally - the driver will return 0, in which case it must cancel all - outstanding URBs (usb_kill_urb()) and not submit any more. - - The resume method is called to tell the driver that the - device has been resumed and the driver can return to normal - operation. URBs may once more be submitted. - - The reset_resume method is called to tell the driver that - the device has been resumed and it also has been reset. - The driver should redo any necessary device initialization, - since the device has probably lost most or all of its state - (although the interfaces will be in the same altsettings as - before the suspend). - -If the device is disconnected or powered down while it is suspended, -the disconnect method will be called instead of the resume or -reset_resume method. This is also quite likely to happen when -waking up from hibernation, as many systems do not maintain suspend -current to the USB host controllers during hibernation. (It's -possible to work around the hibernation-forces-disconnect problem by -using the USB Persist facility.) - -The reset_resume method is used by the USB Persist facility (see -Documentation/usb/persist.txt) and it can also be used under certain -circumstances when CONFIG_USB_PERSIST is not enabled. Currently, if a -device is reset during a resume and the driver does not have a -reset_resume method, the driver won't receive any notification about -the resume. Later kernels will call the driver's disconnect method; -2.6.23 doesn't do this. - -USB drivers are bound to interfaces, so their suspend and resume -methods get called when the interfaces are suspended or resumed. In -principle one might want to suspend some interfaces on a device (i.e., -force the drivers for those interface to stop all activity) without -suspending the other interfaces. The USB core doesn't allow this; all -interfaces are suspended when the device itself is suspended and all -interfaces are resumed when the device is resumed. It isn't possible -to suspend or resume some but not all of a device's interfaces. The -closest you can come is to unbind the interfaces' drivers. - - - The driver interface for autosuspend and autoresume - --------------------------------------------------- - -To support autosuspend and autoresume, a driver should implement all -three of the methods listed above. In addition, a driver indicates -that it supports autosuspend by setting the .supports_autosuspend flag -in its usb_driver structure. It is then responsible for informing the -USB core whenever one of its interfaces becomes busy or idle. The -driver does so by calling these six functions: - - int usb_autopm_get_interface(struct usb_interface *intf); - void usb_autopm_put_interface(struct usb_interface *intf); - int usb_autopm_get_interface_async(struct usb_interface *intf); - void usb_autopm_put_interface_async(struct usb_interface *intf); - void usb_autopm_get_interface_no_resume(struct usb_interface *intf); - void usb_autopm_put_interface_no_suspend(struct usb_interface *intf); - -The functions work by maintaining a usage counter in the -usb_interface's embedded device structure. When the counter is > 0 -then the interface is deemed to be busy, and the kernel will not -autosuspend the interface's device. When the usage counter is = 0 -then the interface is considered to be idle, and the kernel may -autosuspend the device. - -Drivers need not be concerned about balancing changes to the usage -counter; the USB core will undo any remaining "get"s when a driver -is unbound from its interface. As a corollary, drivers must not call -any of the usb_autopm_* functions after their disconnect() routine has -returned. - -Drivers using the async routines are responsible for their own -synchronization and mutual exclusion. - - usb_autopm_get_interface() increments the usage counter and - does an autoresume if the device is suspended. If the - autoresume fails, the counter is decremented back. - - usb_autopm_put_interface() decrements the usage counter and - attempts an autosuspend if the new value is = 0. - - usb_autopm_get_interface_async() and - usb_autopm_put_interface_async() do almost the same things as - their non-async counterparts. The big difference is that they - use a workqueue to do the resume or suspend part of their - jobs. As a result they can be called in an atomic context, - such as an URB's completion handler, but when they return the - device will generally not yet be in the desired state. - - usb_autopm_get_interface_no_resume() and - usb_autopm_put_interface_no_suspend() merely increment or - decrement the usage counter; they do not attempt to carry out - an autoresume or an autosuspend. Hence they can be called in - an atomic context. - -The simplest usage pattern is that a driver calls -usb_autopm_get_interface() in its open routine and -usb_autopm_put_interface() in its close or release routine. But other -patterns are possible. - -The autosuspend attempts mentioned above will often fail for one -reason or another. For example, the power/control attribute might be -set to "on", or another interface in the same device might not be -idle. This is perfectly normal. If the reason for failure was that -the device hasn't been idle for long enough, a timer is scheduled to -carry out the operation automatically when the autosuspend idle-delay -has expired. - -Autoresume attempts also can fail, although failure would mean that -the device is no longer present or operating properly. Unlike -autosuspend, there's no idle-delay for an autoresume. - - - Other parts of the driver interface - ----------------------------------- - -Drivers can enable autosuspend for their devices by calling - - usb_enable_autosuspend(struct usb_device *udev); - -in their probe() routine, if they know that the device is capable of -suspending and resuming correctly. This is exactly equivalent to -writing "auto" to the device's power/control attribute. Likewise, -drivers can disable autosuspend by calling - - usb_disable_autosuspend(struct usb_device *udev); - -This is exactly the same as writing "on" to the power/control attribute. - -Sometimes a driver needs to make sure that remote wakeup is enabled -during autosuspend. For example, there's not much point -autosuspending a keyboard if the user can't cause the keyboard to do a -remote wakeup by typing on it. If the driver sets -intf->needs_remote_wakeup to 1, the kernel won't autosuspend the -device if remote wakeup isn't available. (If the device is already -autosuspended, though, setting this flag won't cause the kernel to -autoresume it. Normally a driver would set this flag in its probe -method, at which time the device is guaranteed not to be -autosuspended.) - -If a driver does its I/O asynchronously in interrupt context, it -should call usb_autopm_get_interface_async() before starting output and -usb_autopm_put_interface_async() when the output queue drains. When -it receives an input event, it should call - - usb_mark_last_busy(struct usb_device *udev); - -in the event handler. This tells the PM core that the device was just -busy and therefore the next autosuspend idle-delay expiration should -be pushed back. Many of the usb_autopm_* routines also make this call, -so drivers need to worry only when interrupt-driven input arrives. - -Asynchronous operation is always subject to races. For example, a -driver may call the usb_autopm_get_interface_async() routine at a time -when the core has just finished deciding the device has been idle for -long enough but not yet gotten around to calling the driver's suspend -method. The suspend method must be responsible for synchronizing with -the I/O request routine and the URB completion handler; it should -cause autosuspends to fail with -EBUSY if the driver needs to use the -device. - -External suspend calls should never be allowed to fail in this way, -only autosuspend calls. The driver can tell them apart by applying -the PMSG_IS_AUTO() macro to the message argument to the suspend -method; it will return True for internal PM events (autosuspend) and -False for external PM events. - - - Mutual exclusion - ---------------- - -For external events -- but not necessarily for autosuspend or -autoresume -- the device semaphore (udev->dev.sem) will be held when a -suspend or resume method is called. This implies that external -suspend/resume events are mutually exclusive with calls to probe, -disconnect, pre_reset, and post_reset; the USB core guarantees that -this is true of autosuspend/autoresume events as well. - -If a driver wants to block all suspend/resume calls during some -critical section, the best way is to lock the device and call -usb_autopm_get_interface() (and do the reverse at the end of the -critical section). Holding the device semaphore will block all -external PM calls, and the usb_autopm_get_interface() will prevent any -internal PM calls, even if it fails. (Exercise: Why?) - - - Interaction between dynamic PM and system PM - -------------------------------------------- - -Dynamic power management and system power management can interact in -a couple of ways. - -Firstly, a device may already be autosuspended when a system suspend -occurs. Since system suspends are supposed to be as transparent as -possible, the device should remain suspended following the system -resume. But this theory may not work out well in practice; over time -the kernel's behavior in this regard has changed. As of 2.6.37 the -policy is to resume all devices during a system resume and let them -handle their own runtime suspends afterward. - -Secondly, a dynamic power-management event may occur as a system -suspend is underway. The window for this is short, since system -suspends don't take long (a few seconds usually), but it can happen. -For example, a suspended device may send a remote-wakeup signal while -the system is suspending. The remote wakeup may succeed, which would -cause the system suspend to abort. If the remote wakeup doesn't -succeed, it may still remain active and thus cause the system to -resume as soon as the system suspend is complete. Or the remote -wakeup may fail and get lost. Which outcome occurs depends on timing -and on the hardware and firmware design. - - - xHCI hardware link PM - --------------------- - -xHCI host controller provides hardware link power management to usb2.0 -(xHCI 1.0 feature) and usb3.0 devices which support link PM. By -enabling hardware LPM, the host can automatically put the device into -lower power state(L1 for usb2.0 devices, or U1/U2 for usb3.0 devices), -which state device can enter and resume very quickly. - -The user interface for controlling hardware LPM is located in the -power/ subdirectory of each USB device's sysfs directory, that is, in -/sys/bus/usb/devices/.../power/ where "..." is the device's ID. The -relevant attribute files are usb2_hardware_lpm and usb3_hardware_lpm. - - power/usb2_hardware_lpm - - When a USB2 device which support LPM is plugged to a - xHCI host root hub which support software LPM, the - host will run a software LPM test for it; if the device - enters L1 state and resume successfully and the host - supports USB2 hardware LPM, this file will show up and - driver will enable hardware LPM for the device. You - can write y/Y/1 or n/N/0 to the file to enable/disable - USB2 hardware LPM manually. This is for test purpose mainly. - - power/usb3_hardware_lpm_u1 - power/usb3_hardware_lpm_u2 - - When a USB 3.0 lpm-capable device is plugged in to a - xHCI host which supports link PM, it will check if U1 - and U2 exit latencies have been set in the BOS - descriptor; if the check is passed and the host - supports USB3 hardware LPM, USB3 hardware LPM will be - enabled for the device and these files will be created. - The files hold a string value (enable or disable) - indicating whether or not USB3 hardware LPM U1 or U2 - is enabled for the device. - - USB Port Power Control - ---------------------- - -In addition to suspending endpoint devices and enabling hardware -controlled link power management, the USB subsystem also has the -capability to disable power to ports under some conditions. Power is -controlled through Set/ClearPortFeature(PORT_POWER) requests to a hub. -In the case of a root or platform-internal hub the host controller -driver translates PORT_POWER requests into platform firmware (ACPI) -method calls to set the port power state. For more background see the -Linux Plumbers Conference 2012 slides [1] and video [2]: - -Upon receiving a ClearPortFeature(PORT_POWER) request a USB port is -logically off, and may trigger the actual loss of VBUS to the port [3]. -VBUS may be maintained in the case where a hub gangs multiple ports into -a shared power well causing power to remain until all ports in the gang -are turned off. VBUS may also be maintained by hub ports configured for -a charging application. In any event a logically off port will lose -connection with its device, not respond to hotplug events, and not -respond to remote wakeup events*. - -WARNING: turning off a port may result in the inability to hot add a device. -Please see "User Interface for Port Power Control" for details. - -As far as the effect on the device itself it is similar to what a device -goes through during system suspend, i.e. the power session is lost. Any -USB device or driver that misbehaves with system suspend will be -similarly affected by a port power cycle event. For this reason the -implementation shares the same device recovery path (and honors the same -quirks) as the system resume path for the hub. - -[1]: http://dl.dropbox.com/u/96820575/sarah-sharp-lpt-port-power-off2-mini.pdf -[2]: http://linuxplumbers.ubicast.tv/videos/usb-port-power-off-kerneluserspace-api/ -[3]: USB 3.1 Section 10.12 -* wakeup note: if a device is configured to send wakeup events the port - power control implementation will block poweroff attempts on that - port. - - - User Interface for Port Power Control - ------------------------------------- - -The port power control mechanism uses the PM runtime system. Poweroff is -requested by clearing the power/pm_qos_no_power_off flag of the port device -(defaults to 1). If the port is disconnected it will immediately receive a -ClearPortFeature(PORT_POWER) request. Otherwise, it will honor the pm runtime -rules and require the attached child device and all descendants to be suspended. -This mechanism is dependent on the hub advertising port power switching in its -hub descriptor (wHubCharacteristics logical power switching mode field). - -Note, some interface devices/drivers do not support autosuspend. Userspace may -need to unbind the interface drivers before the usb_device will suspend. An -unbound interface device is suspended by default. When unbinding, be careful -to unbind interface drivers, not the driver of the parent usb device. Also, -leave hub interface drivers bound. If the driver for the usb device (not -interface) is unbound the kernel is no longer able to resume the device. If a -hub interface driver is unbound, control of its child ports is lost and all -attached child-devices will disconnect. A good rule of thumb is that if the -'driver/module' link for a device points to /sys/module/usbcore then unbinding -it will interfere with port power control. - -Example of the relevant files for port power control. Note, in this example -these files are relative to a usb hub device (prefix). - - prefix=/sys/devices/pci0000:00/0000:00:14.0/usb3/3-1 - - attached child device + - hub port device + | - hub interface device + | | - v v v - $prefix/3-1:1.0/3-1-port1/device - - $prefix/3-1:1.0/3-1-port1/power/pm_qos_no_power_off - $prefix/3-1:1.0/3-1-port1/device/power/control - $prefix/3-1:1.0/3-1-port1/device/3-1.1:<intf0>/driver/unbind - $prefix/3-1:1.0/3-1-port1/device/3-1.1:<intf1>/driver/unbind - ... - $prefix/3-1:1.0/3-1-port1/device/3-1.1:<intfN>/driver/unbind - -In addition to these files some ports may have a 'peer' link to a port on -another hub. The expectation is that all superspeed ports have a -hi-speed peer. - -$prefix/3-1:1.0/3-1-port1/peer -> ../../../../usb2/2-1/2-1:1.0/2-1-port1 -../../../../usb2/2-1/2-1:1.0/2-1-port1/peer -> ../../../../usb3/3-1/3-1:1.0/3-1-port1 - -Distinct from 'companion ports', or 'ehci/xhci shared switchover ports' -peer ports are simply the hi-speed and superspeed interface pins that -are combined into a single usb3 connector. Peer ports share the same -ancestor XHCI device. - -While a superspeed port is powered off a device may downgrade its -connection and attempt to connect to the hi-speed pins. The -implementation takes steps to prevent this: - -1/ Port suspend is sequenced to guarantee that hi-speed ports are powered-off - before their superspeed peer is permitted to power-off. The implication is - that the setting pm_qos_no_power_off to zero on a superspeed port may not cause - the port to power-off until its highspeed peer has gone to its runtime suspend - state. Userspace must take care to order the suspensions if it wants to - guarantee that a superspeed port will power-off. - -2/ Port resume is sequenced to force a superspeed port to power-on prior to its - highspeed peer. - -3/ Port resume always triggers an attached child device to resume. After a - power session is lost the device may have been removed, or need reset. - Resuming the child device when the parent port regains power resolves those - states and clamps the maximum port power cycle frequency at the rate the child - device can suspend (autosuspend-delay) and resume (reset-resume latency). - -Sysfs files relevant for port power control: - <hubdev-portX>/power/pm_qos_no_power_off: - This writable flag controls the state of an idle port. - Once all children and descendants have suspended the - port may suspend/poweroff provided that - pm_qos_no_power_off is '0'. If pm_qos_no_power_off is - '1' the port will remain active/powered regardless of - the stats of descendants. Defaults to 1. - - <hubdev-portX>/power/runtime_status: - This file reflects whether the port is 'active' (power is on) - or 'suspended' (logically off). There is no indication to - userspace whether VBUS is still supplied. - - <hubdev-portX>/connect_type: - An advisory read-only flag to userspace indicating the - location and connection type of the port. It returns - one of four values 'hotplug', 'hardwired', 'not used', - and 'unknown'. All values, besides unknown, are set by - platform firmware. - - "hotplug" indicates an externally connectable/visible - port on the platform. Typically userspace would choose - to keep such a port powered to handle new device - connection events. - - "hardwired" refers to a port that is not visible but - connectable. Examples are internal ports for USB - bluetooth that can be disconnected via an external - switch or a port with a hardwired USB camera. It is - expected to be safe to allow these ports to suspend - provided pm_qos_no_power_off is coordinated with any - switch that gates connections. Userspace must arrange - for the device to be connected prior to the port - powering off, or to activate the port prior to enabling - connection via a switch. - - "not used" refers to an internal port that is expected - to never have a device connected to it. These may be - empty internal ports, or ports that are not physically - exposed on a platform. Considered safe to be - powered-off at all times. - - "unknown" means platform firmware does not provide - information for this port. Most commonly refers to - external hub ports which should be considered 'hotplug' - for policy decisions. - - NOTE1: since we are relying on the BIOS to get this ACPI - information correct, the USB port descriptions may be - missing or wrong. - - NOTE2: Take care in clearing pm_qos_no_power_off. Once - power is off this port will - not respond to new connect events. - - Once a child device is attached additional constraints are - applied before the port is allowed to poweroff. - - <child>/power/control: - Must be 'auto', and the port will not - power down until <child>/power/runtime_status - reflects the 'suspended' state. Default - value is controlled by child device driver. - - <child>/power/persist: - This defaults to '1' for most devices and indicates if - kernel can persist the device's configuration across a - power session loss (suspend / port-power event). When - this value is '0' (quirky devices), port poweroff is - disabled. - - <child>/driver/unbind: - Wakeup capable devices will block port poweroff. At - this time the only mechanism to clear the usb-internal - wakeup-capability for an interface device is to unbind - its driver. - -Summary of poweroff pre-requisite settings relative to a port device: - - echo 0 > power/pm_qos_no_power_off - echo 0 > peer/power/pm_qos_no_power_off # if it exists - echo auto > power/control # this is the default value - echo auto > <child>/power/control - echo 1 > <child>/power/persist # this is the default value - - Suggested Userspace Port Power Policy - ------------------------------------- - -As noted above userspace needs to be careful and deliberate about what -ports are enabled for poweroff. - -The default configuration is that all ports start with -power/pm_qos_no_power_off set to '1' causing ports to always remain -active. - -Given confidence in the platform firmware's description of the ports -(ACPI _PLD record for a port populates 'connect_type') userspace can -clear pm_qos_no_power_off for all 'not used' ports. The same can be -done for 'hardwired' ports provided poweroff is coordinated with any -connection switch for the port. - -A more aggressive userspace policy is to enable USB port power off for -all ports (set <hubdev-portX>/power/pm_qos_no_power_off to '0') when -some external factor indicates the user has stopped interacting with the -system. For example, a distro may want to enable power off all USB -ports when the screen blanks, and re-power them when the screen becomes -active. Smart phones and tablets may want to power off USB ports when -the user pushes the power button. diff --git a/Documentation/usb/proc_usb_info.txt b/Documentation/usb/proc_usb_info.txt deleted file mode 100644 index 98be91982677..000000000000 --- a/Documentation/usb/proc_usb_info.txt +++ /dev/null @@ -1,390 +0,0 @@ -/proc/bus/usb filesystem output -=============================== -(version 2010.09.13) - - -The usbfs filesystem for USB devices is traditionally mounted at -/proc/bus/usb. It provides the /proc/bus/usb/devices file, as well as -the /proc/bus/usb/BBB/DDD files. - -In many modern systems the usbfs filesystem isn't used at all. Instead -USB device nodes are created under /dev/usb/ or someplace similar. The -"devices" file is available in debugfs, typically as -/sys/kernel/debug/usb/devices. - - -**NOTE**: If /proc/bus/usb appears empty, and a host controller - driver has been linked, then you need to mount the - filesystem. Issue the command (as root): - - mount -t usbfs none /proc/bus/usb - - An alternative and more permanent method would be to add - - none /proc/bus/usb usbfs defaults 0 0 - - to /etc/fstab. This will mount usbfs at each reboot. - You can then issue `cat /proc/bus/usb/devices` to extract - USB device information, and user mode drivers can use usbfs - to interact with USB devices. - - There are a number of mount options supported by usbfs. - Consult the source code (linux/drivers/usb/core/inode.c) for - information about those options. - -**NOTE**: The filesystem has been renamed from "usbdevfs" to - "usbfs", to reduce confusion with "devfs". You may - still see references to the older "usbdevfs" name. - -For more information on mounting the usbfs file system, see the -"USB Device Filesystem" section of the USB Guide. The latest copy -of the USB Guide can be found at http://www.linux-usb.org/ - - -THE /proc/bus/usb/BBB/DDD FILES: --------------------------------- -Each connected USB device has one file. The BBB indicates the bus -number. The DDD indicates the device address on that bus. Both -of these numbers are assigned sequentially, and can be reused, so -you can't rely on them for stable access to devices. For example, -it's relatively common for devices to re-enumerate while they are -still connected (perhaps someone jostled their power supply, hub, -or USB cable), so a device might be 002/027 when you first connect -it and 002/048 sometime later. - -These files can be read as binary data. The binary data consists -of first the device descriptor, then the descriptors for each -configuration of the device. Multi-byte fields in the device descriptor -are converted to host endianness by the kernel. The configuration -descriptors are in bus endian format! The configuration descriptor -are wTotalLength bytes apart. If a device returns less configuration -descriptor data than indicated by wTotalLength there will be a hole in -the file for the missing bytes. This information is also shown -in text form by the /proc/bus/usb/devices file, described later. - -These files may also be used to write user-level drivers for the USB -devices. You would open the /proc/bus/usb/BBB/DDD file read/write, -read its descriptors to make sure it's the device you expect, and then -bind to an interface (or perhaps several) using an ioctl call. You -would issue more ioctls to the device to communicate to it using -control, bulk, or other kinds of USB transfers. The IOCTLs are -listed in the <linux/usbdevice_fs.h> file, and at this writing the -source code (linux/drivers/usb/core/devio.c) is the primary reference -for how to access devices through those files. - -Note that since by default these BBB/DDD files are writable only by -root, only root can write such user mode drivers. You can selectively -grant read/write permissions to other users by using "chmod". Also, -usbfs mount options such as "devmode=0666" may be helpful. - - - -THE /proc/bus/usb/devices FILE: -------------------------------- -In /proc/bus/usb/devices, each device's output has multiple -lines of ASCII output. -I made it ASCII instead of binary on purpose, so that someone -can obtain some useful data from it without the use of an -auxiliary program. However, with an auxiliary program, the numbers -in the first 4 columns of each "T:" line (topology info: -Lev, Prnt, Port, Cnt) can be used to build a USB topology diagram. - -Each line is tagged with a one-character ID for that line: - -T = Topology (etc.) -B = Bandwidth (applies only to USB host controllers, which are - virtualized as root hubs) -D = Device descriptor info. -P = Product ID info. (from Device descriptor, but they won't fit - together on one line) -S = String descriptors. -C = Configuration descriptor info. (* = active configuration) -I = Interface descriptor info. -E = Endpoint descriptor info. - -======================================================================= - -/proc/bus/usb/devices output format: - -Legend: - d = decimal number (may have leading spaces or 0's) - x = hexadecimal number (may have leading spaces or 0's) - s = string - - -Topology info: - -T: Bus=dd Lev=dd Prnt=dd Port=dd Cnt=dd Dev#=ddd Spd=dddd MxCh=dd -| | | | | | | | |__MaxChildren -| | | | | | | |__Device Speed in Mbps -| | | | | | |__DeviceNumber -| | | | | |__Count of devices at this level -| | | | |__Connector/Port on Parent for this device -| | | |__Parent DeviceNumber -| | |__Level in topology for this bus -| |__Bus number -|__Topology info tag - - Speed may be: - 1.5 Mbit/s for low speed USB - 12 Mbit/s for full speed USB - 480 Mbit/s for high speed USB (added for USB 2.0); - also used for Wireless USB, which has no fixed speed - 5000 Mbit/s for SuperSpeed USB (added for USB 3.0) - - For reasons lost in the mists of time, the Port number is always - too low by 1. For example, a device plugged into port 4 will - show up with "Port=03". - -Bandwidth info: -B: Alloc=ddd/ddd us (xx%), #Int=ddd, #Iso=ddd -| | | |__Number of isochronous requests -| | |__Number of interrupt requests -| |__Total Bandwidth allocated to this bus -|__Bandwidth info tag - - Bandwidth allocation is an approximation of how much of one frame - (millisecond) is in use. It reflects only periodic transfers, which - are the only transfers that reserve bandwidth. Control and bulk - transfers use all other bandwidth, including reserved bandwidth that - is not used for transfers (such as for short packets). - - The percentage is how much of the "reserved" bandwidth is scheduled by - those transfers. For a low or full speed bus (loosely, "USB 1.1"), - 90% of the bus bandwidth is reserved. For a high speed bus (loosely, - "USB 2.0") 80% is reserved. - - -Device descriptor info & Product ID info: - -D: Ver=x.xx Cls=xx(s) Sub=xx Prot=xx MxPS=dd #Cfgs=dd -P: Vendor=xxxx ProdID=xxxx Rev=xx.xx - -where -D: Ver=x.xx Cls=xx(sssss) Sub=xx Prot=xx MxPS=dd #Cfgs=dd -| | | | | | |__NumberConfigurations -| | | | | |__MaxPacketSize of Default Endpoint -| | | | |__DeviceProtocol -| | | |__DeviceSubClass -| | |__DeviceClass -| |__Device USB version -|__Device info tag #1 - -where -P: Vendor=xxxx ProdID=xxxx Rev=xx.xx -| | | |__Product revision number -| | |__Product ID code -| |__Vendor ID code -|__Device info tag #2 - - -String descriptor info: - -S: Manufacturer=ssss -| |__Manufacturer of this device as read from the device. -| For USB host controller drivers (virtual root hubs) this may -| be omitted, or (for newer drivers) will identify the kernel -| version and the driver which provides this hub emulation. -|__String info tag - -S: Product=ssss -| |__Product description of this device as read from the device. -| For older USB host controller drivers (virtual root hubs) this -| indicates the driver; for newer ones, it's a product (and vendor) -| description that often comes from the kernel's PCI ID database. -|__String info tag - -S: SerialNumber=ssss -| |__Serial Number of this device as read from the device. -| For USB host controller drivers (virtual root hubs) this is -| some unique ID, normally a bus ID (address or slot name) that -| can't be shared with any other device. -|__String info tag - - - -Configuration descriptor info: - -C:* #Ifs=dd Cfg#=dd Atr=xx MPwr=dddmA -| | | | | |__MaxPower in mA -| | | | |__Attributes -| | | |__ConfiguratioNumber -| | |__NumberOfInterfaces -| |__ "*" indicates the active configuration (others are " ") -|__Config info tag - - USB devices may have multiple configurations, each of which act - rather differently. For example, a bus-powered configuration - might be much less capable than one that is self-powered. Only - one device configuration can be active at a time; most devices - have only one configuration. - - Each configuration consists of one or more interfaces. Each - interface serves a distinct "function", which is typically bound - to a different USB device driver. One common example is a USB - speaker with an audio interface for playback, and a HID interface - for use with software volume control. - - -Interface descriptor info (can be multiple per Config): - -I:* If#=dd Alt=dd #EPs=dd Cls=xx(sssss) Sub=xx Prot=xx Driver=ssss -| | | | | | | | |__Driver name -| | | | | | | | or "(none)" -| | | | | | | |__InterfaceProtocol -| | | | | | |__InterfaceSubClass -| | | | | |__InterfaceClass -| | | | |__NumberOfEndpoints -| | | |__AlternateSettingNumber -| | |__InterfaceNumber -| |__ "*" indicates the active altsetting (others are " ") -|__Interface info tag - - A given interface may have one or more "alternate" settings. - For example, default settings may not use more than a small - amount of periodic bandwidth. To use significant fractions - of bus bandwidth, drivers must select a non-default altsetting. - - Only one setting for an interface may be active at a time, and - only one driver may bind to an interface at a time. Most devices - have only one alternate setting per interface. - - -Endpoint descriptor info (can be multiple per Interface): - -E: Ad=xx(s) Atr=xx(ssss) MxPS=dddd Ivl=dddss -| | | | |__Interval (max) between transfers -| | | |__EndpointMaxPacketSize -| | |__Attributes(EndpointType) -| |__EndpointAddress(I=In,O=Out) -|__Endpoint info tag - - The interval is nonzero for all periodic (interrupt or isochronous) - endpoints. For high speed endpoints the transfer interval may be - measured in microseconds rather than milliseconds. - - For high speed periodic endpoints, the "MaxPacketSize" reflects - the per-microframe data transfer size. For "high bandwidth" - endpoints, that can reflect two or three packets (for up to - 3KBytes every 125 usec) per endpoint. - - With the Linux-USB stack, periodic bandwidth reservations use the - transfer intervals and sizes provided by URBs, which can be less - than those found in endpoint descriptor. - - -======================================================================= - - -If a user or script is interested only in Topology info, for -example, use something like "grep ^T: /proc/bus/usb/devices" -for only the Topology lines. A command like -"grep -i ^[tdp]: /proc/bus/usb/devices" can be used to list -only the lines that begin with the characters in square brackets, -where the valid characters are TDPCIE. With a slightly more able -script, it can display any selected lines (for example, only T, D, -and P lines) and change their output format. (The "procusb" -Perl script is the beginning of this idea. It will list only -selected lines [selected from TBDPSCIE] or "All" lines from -/proc/bus/usb/devices.) - -The Topology lines can be used to generate a graphic/pictorial -of the USB devices on a system's root hub. (See more below -on how to do this.) - -The Interface lines can be used to determine what driver is -being used for each device, and which altsetting it activated. - -The Configuration lines could be used to list maximum power -(in milliamps) that a system's USB devices are using. -For example, "grep ^C: /proc/bus/usb/devices". - - -Here's an example, from a system which has a UHCI root hub, -an external hub connected to the root hub, and a mouse and -a serial converter connected to the external hub. - -T: Bus=00 Lev=00 Prnt=00 Port=00 Cnt=00 Dev#= 1 Spd=12 MxCh= 2 -B: Alloc= 28/900 us ( 3%), #Int= 2, #Iso= 0 -D: Ver= 1.00 Cls=09(hub ) Sub=00 Prot=00 MxPS= 8 #Cfgs= 1 -P: Vendor=0000 ProdID=0000 Rev= 0.00 -S: Product=USB UHCI Root Hub -S: SerialNumber=dce0 -C:* #Ifs= 1 Cfg#= 1 Atr=40 MxPwr= 0mA -I: If#= 0 Alt= 0 #EPs= 1 Cls=09(hub ) Sub=00 Prot=00 Driver=hub -E: Ad=81(I) Atr=03(Int.) MxPS= 8 Ivl=255ms - -T: Bus=00 Lev=01 Prnt=01 Port=00 Cnt=01 Dev#= 2 Spd=12 MxCh= 4 -D: Ver= 1.00 Cls=09(hub ) Sub=00 Prot=00 MxPS= 8 #Cfgs= 1 -P: Vendor=0451 ProdID=1446 Rev= 1.00 -C:* #Ifs= 1 Cfg#= 1 Atr=e0 MxPwr=100mA -I: If#= 0 Alt= 0 #EPs= 1 Cls=09(hub ) Sub=00 Prot=00 Driver=hub -E: Ad=81(I) Atr=03(Int.) MxPS= 1 Ivl=255ms - -T: Bus=00 Lev=02 Prnt=02 Port=00 Cnt=01 Dev#= 3 Spd=1.5 MxCh= 0 -D: Ver= 1.00 Cls=00(>ifc ) Sub=00 Prot=00 MxPS= 8 #Cfgs= 1 -P: Vendor=04b4 ProdID=0001 Rev= 0.00 -C:* #Ifs= 1 Cfg#= 1 Atr=80 MxPwr=100mA -I: If#= 0 Alt= 0 #EPs= 1 Cls=03(HID ) Sub=01 Prot=02 Driver=mouse -E: Ad=81(I) Atr=03(Int.) MxPS= 3 Ivl= 10ms - -T: Bus=00 Lev=02 Prnt=02 Port=02 Cnt=02 Dev#= 4 Spd=12 MxCh= 0 -D: Ver= 1.00 Cls=00(>ifc ) Sub=00 Prot=00 MxPS= 8 #Cfgs= 1 -P: Vendor=0565 ProdID=0001 Rev= 1.08 -S: Manufacturer=Peracom Networks, Inc. -S: Product=Peracom USB to Serial Converter -C:* #Ifs= 1 Cfg#= 1 Atr=a0 MxPwr=100mA -I: If#= 0 Alt= 0 #EPs= 3 Cls=00(>ifc ) Sub=00 Prot=00 Driver=serial -E: Ad=81(I) Atr=02(Bulk) MxPS= 64 Ivl= 16ms -E: Ad=01(O) Atr=02(Bulk) MxPS= 16 Ivl= 16ms -E: Ad=82(I) Atr=03(Int.) MxPS= 8 Ivl= 8ms - - -Selecting only the "T:" and "I:" lines from this (for example, by using -"procusb ti"), we have: - -T: Bus=00 Lev=00 Prnt=00 Port=00 Cnt=00 Dev#= 1 Spd=12 MxCh= 2 -T: Bus=00 Lev=01 Prnt=01 Port=00 Cnt=01 Dev#= 2 Spd=12 MxCh= 4 -I: If#= 0 Alt= 0 #EPs= 1 Cls=09(hub ) Sub=00 Prot=00 Driver=hub -T: Bus=00 Lev=02 Prnt=02 Port=00 Cnt=01 Dev#= 3 Spd=1.5 MxCh= 0 -I: If#= 0 Alt= 0 #EPs= 1 Cls=03(HID ) Sub=01 Prot=02 Driver=mouse -T: Bus=00 Lev=02 Prnt=02 Port=02 Cnt=02 Dev#= 4 Spd=12 MxCh= 0 -I: If#= 0 Alt= 0 #EPs= 3 Cls=00(>ifc ) Sub=00 Prot=00 Driver=serial - - -Physically this looks like (or could be converted to): - - +------------------+ - | PC/root_hub (12)| Dev# = 1 - +------------------+ (nn) is Mbps. - Level 0 | CN.0 | CN.1 | [CN = connector/port #] - +------------------+ - / - / - +-----------------------+ - Level 1 | Dev#2: 4-port hub (12)| - +-----------------------+ - |CN.0 |CN.1 |CN.2 |CN.3 | - +-----------------------+ - \ \____________________ - \_____ \ - \ \ - +--------------------+ +--------------------+ - Level 2 | Dev# 3: mouse (1.5)| | Dev# 4: serial (12)| - +--------------------+ +--------------------+ - - - -Or, in a more tree-like structure (ports [Connectors] without -connections could be omitted): - -PC: Dev# 1, root hub, 2 ports, 12 Mbps -|_ CN.0: Dev# 2, hub, 4 ports, 12 Mbps - |_ CN.0: Dev #3, mouse, 1.5 Mbps - |_ CN.1: - |_ CN.2: Dev #4, serial, 12 Mbps - |_ CN.3: -|_ CN.1: - - - ### END ### |