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| author | Grant Likely <grant.likely@secretlab.ca> | 2011-01-26 10:10:40 -0700 |
|---|---|---|
| committer | Grant Likely <grant.likely@secretlab.ca> | 2011-01-31 00:09:01 -0700 |
| commit | d524dac9279b6a41ffdf7ff7958c577f2e387db6 (patch) | |
| tree | 294166d18a1c89c4cebb2571ea7b124876fb01ef /Documentation/powerpc/booting-without-of.txt | |
| parent | 1bae4ce27c9c90344f23c65ea6966c50ffeae2f5 (diff) | |
| download | lwn-d524dac9279b6a41ffdf7ff7958c577f2e387db6.tar.gz lwn-d524dac9279b6a41ffdf7ff7958c577f2e387db6.zip | |
dt: Move device tree documentation out of powerpc directory
The device tree is used by more than just PowerPC. Make the documentation
directory available to all.
v2: reorganized files while moving to create arch and driver specific
directories.
Signed-off-by: Grant Likely <grant.likely@secretlab.ca>
Acked-by: Josh Boyer <jwboyer@linux.vnet.ibm.com>
Diffstat (limited to 'Documentation/powerpc/booting-without-of.txt')
| -rw-r--r-- | Documentation/powerpc/booting-without-of.txt | 1447 |
1 files changed, 0 insertions, 1447 deletions
diff --git a/Documentation/powerpc/booting-without-of.txt b/Documentation/powerpc/booting-without-of.txt deleted file mode 100644 index 7400d7555dc3..000000000000 --- a/Documentation/powerpc/booting-without-of.txt +++ /dev/null @@ -1,1447 +0,0 @@ - Booting the Linux/ppc kernel without Open Firmware - -------------------------------------------------- - -(c) 2005 Benjamin Herrenschmidt <benh at kernel.crashing.org>, - IBM Corp. -(c) 2005 Becky Bruce <becky.bruce at freescale.com>, - Freescale Semiconductor, FSL SOC and 32-bit additions -(c) 2006 MontaVista Software, Inc. - Flash chip node definition - -Table of Contents -================= - - I - Introduction - 1) Entry point for arch/powerpc - 2) Board support - - II - The DT block format - 1) Header - 2) Device tree generalities - 3) Device tree "structure" block - 4) Device tree "strings" block - - III - Required content of the device tree - 1) Note about cells and address representation - 2) Note about "compatible" properties - 3) Note about "name" properties - 4) Note about node and property names and character set - 5) Required nodes and properties - a) The root node - b) The /cpus node - c) The /cpus/* nodes - d) the /memory node(s) - e) The /chosen node - f) the /soc<SOCname> node - - IV - "dtc", the device tree compiler - - V - Recommendations for a bootloader - - VI - System-on-a-chip devices and nodes - 1) Defining child nodes of an SOC - 2) Representing devices without a current OF specification - a) PHY nodes - b) Interrupt controllers - c) 4xx/Axon EMAC ethernet nodes - d) Xilinx IP cores - e) USB EHCI controllers - f) MDIO on GPIOs - g) SPI busses - - VII - Specifying interrupt information for devices - 1) interrupts property - 2) interrupt-parent property - 3) OpenPIC Interrupt Controllers - 4) ISA Interrupt Controllers - - VIII - Specifying device power management information (sleep property) - - Appendix A - Sample SOC node for MPC8540 - - -Revision Information -==================== - - May 18, 2005: Rev 0.1 - Initial draft, no chapter III yet. - - May 19, 2005: Rev 0.2 - Add chapter III and bits & pieces here or - clarifies the fact that a lot of things are - optional, the kernel only requires a very - small device tree, though it is encouraged - to provide an as complete one as possible. - - May 24, 2005: Rev 0.3 - Precise that DT block has to be in RAM - - Misc fixes - - Define version 3 and new format version 16 - for the DT block (version 16 needs kernel - patches, will be fwd separately). - String block now has a size, and full path - is replaced by unit name for more - compactness. - linux,phandle is made optional, only nodes - that are referenced by other nodes need it. - "name" property is now automatically - deduced from the unit name - - June 1, 2005: Rev 0.4 - Correct confusion between OF_DT_END and - OF_DT_END_NODE in structure definition. - - Change version 16 format to always align - property data to 4 bytes. Since tokens are - already aligned, that means no specific - required alignment between property size - and property data. The old style variable - alignment would make it impossible to do - "simple" insertion of properties using - memmove (thanks Milton for - noticing). Updated kernel patch as well - - Correct a few more alignment constraints - - Add a chapter about the device-tree - compiler and the textural representation of - the tree that can be "compiled" by dtc. - - November 21, 2005: Rev 0.5 - - Additions/generalizations for 32-bit - - Changed to reflect the new arch/powerpc - structure - - Added chapter VI - - - ToDo: - - Add some definitions of interrupt tree (simple/complex) - - Add some definitions for PCI host bridges - - Add some common address format examples - - Add definitions for standard properties and "compatible" - names for cells that are not already defined by the existing - OF spec. - - Compare FSL SOC use of PCI to standard and make sure no new - node definition required. - - Add more information about node definitions for SOC devices - that currently have no standard, like the FSL CPM. - - -I - Introduction -================ - -During the recent development of the Linux/ppc64 kernel, and more -specifically, the addition of new platform types outside of the old -IBM pSeries/iSeries pair, it was decided to enforce some strict rules -regarding the kernel entry and bootloader <-> kernel interfaces, in -order to avoid the degeneration that had become the ppc32 kernel entry -point and the way a new platform should be added to the kernel. The -legacy iSeries platform breaks those rules as it predates this scheme, -but no new board support will be accepted in the main tree that -doesn't follow them properly. In addition, since the advent of the -arch/powerpc merged architecture for ppc32 and ppc64, new 32-bit -platforms and 32-bit platforms which move into arch/powerpc will be -required to use these rules as well. - -The main requirement that will be defined in more detail below is -the presence of a device-tree whose format is defined after Open -Firmware specification. However, in order to make life easier -to embedded board vendors, the kernel doesn't require the device-tree -to represent every device in the system and only requires some nodes -and properties to be present. This will be described in detail in -section III, but, for example, the kernel does not require you to -create a node for every PCI device in the system. It is a requirement -to have a node for PCI host bridges in order to provide interrupt -routing informations and memory/IO ranges, among others. It is also -recommended to define nodes for on chip devices and other busses that -don't specifically fit in an existing OF specification. This creates a -great flexibility in the way the kernel can then probe those and match -drivers to device, without having to hard code all sorts of tables. It -also makes it more flexible for board vendors to do minor hardware -upgrades without significantly impacting the kernel code or cluttering -it with special cases. - - -1) Entry point for arch/powerpc -------------------------------- - - There is one and one single entry point to the kernel, at the start - of the kernel image. That entry point supports two calling - conventions: - - a) Boot from Open Firmware. If your firmware is compatible - with Open Firmware (IEEE 1275) or provides an OF compatible - client interface API (support for "interpret" callback of - forth words isn't required), you can enter the kernel with: - - r5 : OF callback pointer as defined by IEEE 1275 - bindings to powerpc. Only the 32-bit client interface - is currently supported - - r3, r4 : address & length of an initrd if any or 0 - - The MMU is either on or off; the kernel will run the - trampoline located in arch/powerpc/kernel/prom_init.c to - extract the device-tree and other information from open - firmware and build a flattened device-tree as described - in b). prom_init() will then re-enter the kernel using - the second method. This trampoline code runs in the - context of the firmware, which is supposed to handle all - exceptions during that time. - - b) Direct entry with a flattened device-tree block. This entry - point is called by a) after the OF trampoline and can also be - called directly by a bootloader that does not support the Open - Firmware client interface. It is also used by "kexec" to - implement "hot" booting of a new kernel from a previous - running one. This method is what I will describe in more - details in this document, as method a) is simply standard Open - Firmware, and thus should be implemented according to the - various standard documents defining it and its binding to the - PowerPC platform. The entry point definition then becomes: - - r3 : physical pointer to the device-tree block - (defined in chapter II) in RAM - - r4 : physical pointer to the kernel itself. This is - used by the assembly code to properly disable the MMU - in case you are entering the kernel with MMU enabled - and a non-1:1 mapping. - - r5 : NULL (as to differentiate with method a) - - Note about SMP entry: Either your firmware puts your other - CPUs in some sleep loop or spin loop in ROM where you can get - them out via a soft reset or some other means, in which case - you don't need to care, or you'll have to enter the kernel - with all CPUs. The way to do that with method b) will be - described in a later revision of this document. - - -2) Board support ----------------- - -64-bit kernels: - - Board supports (platforms) are not exclusive config options. An - arbitrary set of board supports can be built in a single kernel - image. The kernel will "know" what set of functions to use for a - given platform based on the content of the device-tree. Thus, you - should: - - a) add your platform support as a _boolean_ option in - arch/powerpc/Kconfig, following the example of PPC_PSERIES, - PPC_PMAC and PPC_MAPLE. The later is probably a good - example of a board support to start from. - - b) create your main platform file as - "arch/powerpc/platforms/myplatform/myboard_setup.c" and add it - to the Makefile under the condition of your CONFIG_ - option. This file will define a structure of type "ppc_md" - containing the various callbacks that the generic code will - use to get to your platform specific code - - c) Add a reference to your "ppc_md" structure in the - "machines" table in arch/powerpc/kernel/setup_64.c if you are - a 64-bit platform. - - d) request and get assigned a platform number (see PLATFORM_* - constants in arch/powerpc/include/asm/processor.h - -32-bit embedded kernels: - - Currently, board support is essentially an exclusive config option. - The kernel is configured for a single platform. Part of the reason - for this is to keep kernels on embedded systems small and efficient; - part of this is due to the fact the code is already that way. In the - future, a kernel may support multiple platforms, but only if the - platforms feature the same core architecture. A single kernel build - cannot support both configurations with Book E and configurations - with classic Powerpc architectures. - - 32-bit embedded platforms that are moved into arch/powerpc using a - flattened device tree should adopt the merged tree practice of - setting ppc_md up dynamically, even though the kernel is currently - built with support for only a single platform at a time. This allows - unification of the setup code, and will make it easier to go to a - multiple-platform-support model in the future. - -NOTE: I believe the above will be true once Ben's done with the merge -of the boot sequences.... someone speak up if this is wrong! - - To add a 32-bit embedded platform support, follow the instructions - for 64-bit platforms above, with the exception that the Kconfig - option should be set up such that the kernel builds exclusively for - the platform selected. The processor type for the platform should - enable another config option to select the specific board - supported. - -NOTE: If Ben doesn't merge the setup files, may need to change this to -point to setup_32.c - - - I will describe later the boot process and various callbacks that - your platform should implement. - - -II - The DT block format -======================== - - -This chapter defines the actual format of the flattened device-tree -passed to the kernel. The actual content of it and kernel requirements -are described later. You can find example of code manipulating that -format in various places, including arch/powerpc/kernel/prom_init.c -which will generate a flattened device-tree from the Open Firmware -representation, or the fs2dt utility which is part of the kexec tools -which will generate one from a filesystem representation. It is -expected that a bootloader like uboot provides a bit more support, -that will be discussed later as well. - -Note: The block has to be in main memory. It has to be accessible in -both real mode and virtual mode with no mapping other than main -memory. If you are writing a simple flash bootloader, it should copy -the block to RAM before passing it to the kernel. - - -1) Header ---------- - - The kernel is entered with r3 pointing to an area of memory that is - roughly described in arch/powerpc/include/asm/prom.h by the structure - boot_param_header: - -struct boot_param_header { - u32 magic; /* magic word OF_DT_HEADER */ - u32 totalsize; /* total size of DT block */ - u32 off_dt_struct; /* offset to structure */ - u32 off_dt_strings; /* offset to strings */ - u32 off_mem_rsvmap; /* offset to memory reserve map - */ - u32 version; /* format version */ - u32 last_comp_version; /* last compatible version */ - - /* version 2 fields below */ - u32 boot_cpuid_phys; /* Which physical CPU id we're - booting on */ - /* version 3 fields below */ - u32 size_dt_strings; /* size of the strings block */ - - /* version 17 fields below */ - u32 size_dt_struct; /* size of the DT structure block */ -}; - - Along with the constants: - -/* Definitions used by the flattened device tree */ -#define OF_DT_HEADER 0xd00dfeed /* 4: version, - 4: total size */ -#define OF_DT_BEGIN_NODE 0x1 /* Start node: full name - */ -#define OF_DT_END_NODE 0x2 /* End node */ -#define OF_DT_PROP 0x3 /* Property: name off, - size, content */ -#define OF_DT_END 0x9 - - All values in this header are in big endian format, the various - fields in this header are defined more precisely below. All - "offset" values are in bytes from the start of the header; that is - from the value of r3. - - - magic - - This is a magic value that "marks" the beginning of the - device-tree block header. It contains the value 0xd00dfeed and is - defined by the constant OF_DT_HEADER - - - totalsize - - This is the total size of the DT block including the header. The - "DT" block should enclose all data structures defined in this - chapter (who are pointed to by offsets in this header). That is, - the device-tree structure, strings, and the memory reserve map. - - - off_dt_struct - - This is an offset from the beginning of the header to the start - of the "structure" part the device tree. (see 2) device tree) - - - off_dt_strings - - This is an offset from the beginning of the header to the start - of the "strings" part of the device-tree - - - off_mem_rsvmap - - This is an offset from the beginning of the header to the start - of the reserved memory map. This map is a list of pairs of 64- - bit integers. Each pair is a physical address and a size. The - list is terminated by an entry of size 0. This map provides the - kernel with a list of physical memory areas that are "reserved" - and thus not to be used for memory allocations, especially during - early initialization. The kernel needs to allocate memory during - boot for things like un-flattening the device-tree, allocating an - MMU hash table, etc... Those allocations must be done in such a - way to avoid overriding critical things like, on Open Firmware - capable machines, the RTAS instance, or on some pSeries, the TCE - tables used for the iommu. Typically, the reserve map should - contain _at least_ this DT block itself (header,total_size). If - you are passing an initrd to the kernel, you should reserve it as - well. You do not need to reserve the kernel image itself. The map - should be 64-bit aligned. - - - version - - This is the version of this structure. Version 1 stops - here. Version 2 adds an additional field boot_cpuid_phys. - Version 3 adds the size of the strings block, allowing the kernel - to reallocate it easily at boot and free up the unused flattened - structure after expansion. Version 16 introduces a new more - "compact" format for the tree itself that is however not backward - compatible. Version 17 adds an additional field, size_dt_struct, - allowing it to be reallocated or moved more easily (this is - particularly useful for bootloaders which need to make - adjustments to a device tree based on probed information). You - should always generate a structure of the highest version defined - at the time of your implementation. Currently that is version 17, - unless you explicitly aim at being backward compatible. - - - last_comp_version - - Last compatible version. This indicates down to what version of - the DT block you are backward compatible. For example, version 2 - is backward compatible with version 1 (that is, a kernel build - for version 1 will be able to boot with a version 2 format). You - should put a 1 in this field if you generate a device tree of - version 1 to 3, or 16 if you generate a tree of version 16 or 17 - using the new unit name format. - - - boot_cpuid_phys - - This field only exist on version 2 headers. It indicate which - physical CPU ID is calling the kernel entry point. This is used, - among others, by kexec. If you are on an SMP system, this value - should match the content of the "reg" property of the CPU node in - the device-tree corresponding to the CPU calling the kernel entry - point (see further chapters for more informations on the required - device-tree contents) - - - size_dt_strings - - This field only exists on version 3 and later headers. It - gives the size of the "strings" section of the device tree (which - starts at the offset given by off_dt_strings). - - - size_dt_struct - - This field only exists on version 17 and later headers. It gives - the size of the "structure" section of the device tree (which - starts at the offset given by off_dt_struct). - - So the typical layout of a DT block (though the various parts don't - need to be in that order) looks like this (addresses go from top to - bottom): - - - ------------------------------ - r3 -> | struct boot_param_header | - ------------------------------ - | (alignment gap) (*) | - ------------------------------ - | memory reserve map | - ------------------------------ - | (alignment gap) | - ------------------------------ - | | - | device-tree structure | - | | - ------------------------------ - | (alignment gap) | - ------------------------------ - | | - | device-tree strings | - | | - -----> ------------------------------ - | - | - --- (r3 + totalsize) - - (*) The alignment gaps are not necessarily present; their presence - and size are dependent on the various alignment requirements of - the individual data blocks. - - -2) Device tree generalities ---------------------------- - -This device-tree itself is separated in two different blocks, a -structure block and a strings block. Both need to be aligned to a 4 -byte boundary. - -First, let's quickly describe the device-tree concept before detailing -the storage format. This chapter does _not_ describe the detail of the -required types of nodes & properties for the kernel, this is done -later in chapter III. - -The device-tree layout is strongly inherited from the definition of -the Open Firmware IEEE 1275 device-tree. It's basically a tree of -nodes, each node having two or more named properties. A property can -have a value or not. - -It is a tree, so each node has one and only one parent except for the -root node who has no parent. - -A node has 2 names. The actual node name is generally contained in a -property of type "name" in the node property list whose value is a -zero terminated string and is mandatory for version 1 to 3 of the -format definition (as it is in Open Firmware). Version 16 makes it -optional as it can generate it from the unit name defined below. - -There is also a "unit name" that is used to differentiate nodes with -the same name at the same level, it is usually made of the node -names, the "@" sign, and a "unit address", which definition is -specific to the bus type the node sits on. - -The unit name doesn't exist as a property per-se but is included in -the device-tree structure. It is typically used to represent "path" in -the device-tree. More details about the actual format of these will be -below. - -The kernel powerpc generic code does not make any formal use of the -unit address (though some board support code may do) so the only real -requirement here for the unit address is to ensure uniqueness of -the node unit name at a given level of the tree. Nodes with no notion -of address and no possible sibling of the same name (like /memory or -/cpus) may omit the unit address in the context of this specification, -or use the "@0" default unit address. The unit name is used to define -a node "full path", which is the concatenation of all parent node -unit names separated with "/". - -The root node doesn't have a defined name, and isn't required to have -a name property either if you are using version 3 or earlier of the -format. It also has no unit address (no @ symbol followed by a unit -address). The root node unit name is thus an empty string. The full -path to the root node is "/". - -Every node which actually represents an actual device (that is, a node -which isn't only a virtual "container" for more nodes, like "/cpus" -is) is also required to have a "device_type" property indicating the -type of node . - -Finally, every node that can be referenced from a property in another -node is required to have a "linux,phandle" property. Real open -firmware implementations provide a unique "phandle" value for every -node that the "prom_init()" trampoline code turns into -"linux,phandle" properties. However, this is made optional if the -flattened device tree is used directly. An example of a node -referencing another node via "phandle" is when laying out the -interrupt tree which will be described in a further version of this -document. - -This "linux, phandle" property is a 32-bit value that uniquely -identifies a node. You are free to use whatever values or system of -values, internal pointers, or whatever to generate these, the only -requirement is that every node for which you provide that property has -a unique value for it. - -Here is an example of a simple device-tree. In this example, an "o" -designates a node followed by the node unit name. Properties are -presented with their name followed by their content. "content" -represents an ASCII string (zero terminated) value, while <content> -represents a 32-bit hexadecimal value. The various nodes in this -example will be discussed in a later chapter. At this point, it is -only meant to give you a idea of what a device-tree looks like. I have -purposefully kept the "name" and "linux,phandle" properties which -aren't necessary in order to give you a better idea of what the tree -looks like in practice. - - / o device-tree - |- name = "device-tree" - |- model = "MyBoardName" - |- compatible = "MyBoardFamilyName" - |- #address-cells = <2> - |- #size-cells = <2> - |- linux,phandle = <0> - | - o cpus - | | - name = "cpus" - | | - linux,phandle = <1> - | | - #address-cells = <1> - | | - #size-cells = <0> - | | - | o PowerPC,970@0 - | |- name = "PowerPC,970" - | |- device_type = "cpu" - | |- reg = <0> - | |- clock-frequency = <5f5e1000> - | |- 64-bit - | |- linux,phandle = <2> - | - o memory@0 - | |- name = "memory" - | |- device_type = "memory" - | |- reg = <00000000 00000000 00000000 20000000> - | |- linux,phandle = <3> - | - o chosen - |- name = "chosen" - |- bootargs = "root=/dev/sda2" - |- linux,phandle = <4> - -This tree is almost a minimal tree. It pretty much contains the -minimal set of required nodes and properties to boot a linux kernel; -that is, some basic model informations at the root, the CPUs, and the -physical memory layout. It also includes misc information passed -through /chosen, like in this example, the platform type (mandatory) -and the kernel command line arguments (optional). - -The /cpus/PowerPC,970@0/64-bit property is an example of a -property without a value. All other properties have a value. The -significance of the #address-cells and #size-cells properties will be -explained in chapter IV which defines precisely the required nodes and -properties and their content. - - -3) Device tree "structure" block - -The structure of the device tree is a linearized tree structure. The -"OF_DT_BEGIN_NODE" token starts a new node, and the "OF_DT_END_NODE" -ends that node definition. Child nodes are simply defined before -"OF_DT_END_NODE" (that is nodes within the node). A 'token' is a 32 -bit value. The tree has to be "finished" with a OF_DT_END token - -Here's the basic structure of a single node: - - * token OF_DT_BEGIN_NODE (that is 0x00000001) - * for version 1 to 3, this is the node full path as a zero - terminated string, starting with "/". For version 16 and later, - this is the node unit name only (or an empty string for the - root node) - * [align gap to next 4 bytes boundary] - * for each property: - * token OF_DT_PROP (that is 0x00000003) - * 32-bit value of property value size in bytes (or 0 if no - value) - * 32-bit value of offset in string block of property name - * property value data if any - * [align gap to next 4 bytes boundary] - * [child nodes if any] - * token OF_DT_END_NODE (that is 0x00000002) - -So the node content can be summarized as a start token, a full path, -a list of properties, a list of child nodes, and an end token. Every -child node is a full node structure itself as defined above. - -NOTE: The above definition requires that all property definitions for -a particular node MUST precede any subnode definitions for that node. -Although the structure would not be ambiguous if properties and -subnodes were intermingled, the kernel parser requires that the -properties come first (up until at least 2.6.22). Any tools -manipulating a flattened tree must take care to preserve this -constraint. - -4) Device tree "strings" block - -In order to save space, property names, which are generally redundant, -are stored separately in the "strings" block. This block is simply the -whole bunch of zero terminated strings for all property names -concatenated together. The device-tree property definitions in the -structure block will contain offset values from the beginning of the -strings block. - - -III - Required content of the device tree -========================================= - -WARNING: All "linux,*" properties defined in this document apply only -to a flattened device-tree. If your platform uses a real -implementation of Open Firmware or an implementation compatible with -the Open Firmware client interface, those properties will be created -by the trampoline code in the kernel's prom_init() file. For example, -that's where you'll have to add code to detect your board model and -set the platform number. However, when using the flattened device-tree -entry point, there is no prom_init() pass, and thus you have to -provide those properties yourself. - - -1) Note about cells and address representation ----------------------------------------------- - -The general rule is documented in the various Open Firmware -documentations. If you choose to describe a bus with the device-tree -and there exist an OF bus binding, then you should follow the -specification. However, the kernel does not require every single -device or bus to be described by the device tree. - -In general, the format of an address for a device is defined by the -parent bus type, based on the #address-cells and #size-cells -properties. Note that the parent's parent definitions of #address-cells -and #size-cells are not inherited so every node with children must specify -them. The kernel requires the root node to have those properties defining -addresses format for devices directly mapped on the processor bus. - -Those 2 properties define 'cells' for representing an address and a -size. A "cell" is a 32-bit number. For example, if both contain 2 -like the example tree given above, then an address and a size are both -composed of 2 cells, and each is a 64-bit number (cells are -concatenated and expected to be in big endian format). Another example -is the way Apple firmware defines them, with 2 cells for an address -and one cell for a size. Most 32-bit implementations should define -#address-cells and #size-cells to 1, which represents a 32-bit value. -Some 32-bit processors allow for physical addresses greater than 32 -bits; these processors should define #address-cells as 2. - -"reg" properties are always a tuple of the type "address size" where -the number of cells of address and size is specified by the bus -#address-cells and #size-cells. When a bus supports various address -spaces and other flags relative to a given address allocation (like -prefetchable, etc...) those flags are usually added to the top level -bits of the physical address. For example, a PCI physical address is -made of 3 cells, the bottom two containing the actual address itself -while the top cell contains address space indication, flags, and pci -bus & device numbers. - -For busses that support dynamic allocation, it's the accepted practice -to then not provide the address in "reg" (keep it 0) though while -providing a flag indicating the address is dynamically allocated, and -then, to provide a separate "assigned-addresses" property that -contains the fully allocated addresses. See the PCI OF bindings for -details. - -In general, a simple bus with no address space bits and no dynamic -allocation is preferred if it reflects your hardware, as the existing -kernel address parsing functions will work out of the box. If you -define a bus type with a more complex address format, including things -like address space bits, you'll have to add a bus translator to the -prom_parse.c file of the recent kernels for your bus type. - -The "reg" property only defines addresses and sizes (if #size-cells is -non-0) within a given bus. In order to translate addresses upward -(that is into parent bus addresses, and possibly into CPU physical -addresses), all busses must contain a "ranges" property. If the -"ranges" property is missing at a given level, it's assumed that -translation isn't possible, i.e., the registers are not visible on the -parent bus. The format of the "ranges" property for a bus is a list -of: - - bus address, parent bus address, size - -"bus address" is in the format of the bus this bus node is defining, -that is, for a PCI bridge, it would be a PCI address. Thus, (bus -address, size) defines a range of addresses for child devices. "parent -bus address" is in the format of the parent bus of this bus. For -example, for a PCI host controller, that would be a CPU address. For a -PCI<->ISA bridge, that would be a PCI address. It defines the base -address in the parent bus where the beginning of that range is mapped. - -For a new 64-bit powerpc board, I recommend either the 2/2 format or -Apple's 2/1 format which is slightly more compact since sizes usually -fit in a single 32-bit word. New 32-bit powerpc boards should use a -1/1 format, unless the processor supports physical addresses greater -than 32-bits, in which case a 2/1 format is recommended. - -Alternatively, the "ranges" property may be empty, indicating that the -registers are visible on the parent bus using an identity mapping -translation. In other words, the parent bus address space is the same -as the child bus address space. - -2) Note about "compatible" properties -------------------------------------- - -These properties are optional, but recommended in devices and the root -node. The format of a "compatible" property is a list of concatenated -zero terminated strings. They allow a device to express its -compatibility with a family of similar devices, in some cases, -allowing a single driver to match against several devices regardless -of their actual names. - -3) Note about "name" properties -------------------------------- - -While earlier users of Open Firmware like OldWorld macintoshes tended -to use the actual device name for the "name" property, it's nowadays -considered a good practice to use a name that is closer to the device -class (often equal to device_type). For example, nowadays, ethernet -controllers are named "ethernet", an additional "model" property -defining precisely the chip type/model, and "compatible" property -defining the family in case a single driver can driver more than one -of these chips. However, the kernel doesn't generally put any -restriction on the "name" property; it is simply considered good -practice to follow the standard and its evolutions as closely as -possible. - -Note also that the new format version 16 makes the "name" property -optional. If it's absent for a node, then the node's unit name is then -used to reconstruct the name. That is, the part of the unit name -before the "@" sign is used (or the entire unit name if no "@" sign -is present). - -4) Note about node and property names and character set -------------------------------------------------------- - -While open firmware provides more flexible usage of 8859-1, this -specification enforces more strict rules. Nodes and properties should -be comprised only of ASCII characters 'a' to 'z', '0' to -'9', ',', '.', '_', '+', '#', '?', and '-'. Node names additionally -allow uppercase characters 'A' to 'Z' (property names should be -lowercase. The fact that vendors like Apple don't respect this rule is -irrelevant here). Additionally, node and property names should always -begin with a character in the range 'a' to 'z' (or 'A' to 'Z' for node -names). - -The maximum number of characters for both nodes and property names -is 31. In the case of node names, this is only the leftmost part of -a unit name (the pure "name" property), it doesn't include the unit -address which can extend beyond that limit. - - -5) Required nodes and properties --------------------------------- - These are all that are currently required. However, it is strongly - recommended that you expose PCI host bridges as documented in the - PCI binding to open firmware, and your interrupt tree as documented - in OF interrupt tree specification. - - a) The root node - - The root node requires some properties to be present: - - - model : this is your board name/model - - #address-cells : address representation for "root" devices - - #size-cells: the size representation for "root" devices - - device_type : This property shouldn't be necessary. However, if - you decide to create a device_type for your root node, make sure it - is _not_ "chrp" unless your platform is a pSeries or PAPR compliant - one for 64-bit, or a CHRP-type machine for 32-bit as this will - matched by the kernel this way. - - Additionally, some recommended properties are: - - - compatible : the board "family" generally finds its way here, - for example, if you have 2 board models with a similar layout, - that typically get driven by the same platform code in the - kernel, you would use a different "model" property but put a - value in "compatible". The kernel doesn't directly use that - value but it is generally useful. - - The root node is also generally where you add additional properties - specific to your board like the serial number if any, that sort of - thing. It is recommended that if you add any "custom" property whose - name may clash with standard defined ones, you prefix them with your - vendor name and a comma. - - b) The /cpus node - - This node is the parent of all individual CPU nodes. It doesn't - have any specific requirements, though it's generally good practice - to have at least: - - #address-cells = <00000001> - #size-cells = <00000000> - - This defines that the "address" for a CPU is a single cell, and has - no meaningful size. This is not necessary but the kernel will assume - that format when reading the "reg" properties of a CPU node, see - below - - c) The /cpus/* nodes - - So under /cpus, you are supposed to create a node for every CPU on - the machine. There is no specific restriction on the name of the - CPU, though It's common practice to call it PowerPC,<name>. For - example, Apple uses PowerPC,G5 while IBM uses PowerPC,970FX. - - Required properties: - - - device_type : has to be "cpu" - - reg : This is the physical CPU number, it's a single 32-bit cell - and is also used as-is as the unit number for constructing the - unit name in the full path. For example, with 2 CPUs, you would - have the full path: - /cpus/PowerPC,970FX@0 - /cpus/PowerPC,970FX@1 - (unit addresses do not require leading zeroes) - - d-cache-block-size : one cell, L1 data cache block size in bytes (*) - - i-cache-block-size : one cell, L1 instruction cache block size in - bytes - - d-cache-size : one cell, size of L1 data cache in bytes - - i-cache-size : one cell, size of L1 instruction cache in bytes - -(*) The cache "block" size is the size on which the cache management -instructions operate. Historically, this document used the cache -"line" size here which is incorrect. The kernel will prefer the cache -block size and will fallback to cache line size for backward -compatibility. - - Recommended properties: - - - timebase-frequency : a cell indicating the frequency of the - timebase in Hz. This is not directly used by the generic code, - but you are welcome to copy/paste the pSeries code for setting - the kernel timebase/decrementer calibration based on this - value. - - clock-frequency : a cell indicating the CPU core clock frequency - in Hz. A new property will be defined for 64-bit values, but if - your frequency is < 4Ghz, one cell is enough. Here as well as - for the above, the common code doesn't use that property, but - you are welcome to re-use the pSeries or Maple one. A future - kernel version might provide a common function for this. - - d-cache-line-size : one cell, L1 data cache line size in bytes - if different from the block size - - i-cache-line-size : one cell, L1 instruction cache line size in - bytes if different from the block size - - You are welcome to add any property you find relevant to your board, - like some information about the mechanism used to soft-reset the - CPUs. For example, Apple puts the GPIO number for CPU soft reset - lines in there as a "soft-reset" property since they start secondary - CPUs by soft-resetting them. - - - d) the /memory node(s) - - To define the physical memory layout of your board, you should - create one or more memory node(s). You can either create a single - node with all memory ranges in its reg property, or you can create - several nodes, as you wish. The unit address (@ part) used for the - full path is the address of the first range of memory defined by a - given node. If you use a single memory node, this will typically be - @0. - - Required properties: - - - device_type : has to be "memory" - - reg : This property contains all the physical memory ranges of - your board. It's a list of addresses/sizes concatenated - together, with the number of cells of each defined by the - #address-cells and #size-cells of the root node. For example, - with both of these properties being 2 like in the example given - earlier, a 970 based machine with 6Gb of RAM could typically - have a "reg" property here that looks like: - - 00000000 00000000 00000000 80000000 - 00000001 00000000 00000001 00000000 - - That is a range starting at 0 of 0x80000000 bytes and a range - starting at 0x100000000 and of 0x100000000 bytes. You can see - that there is no memory covering the IO hole between 2Gb and - 4Gb. Some vendors prefer splitting those ranges into smaller - segments, but the kernel doesn't care. - - e) The /chosen node - - This node is a bit "special". Normally, that's where open firmware - puts some variable environment information, like the arguments, or - the default input/output devices. - - This specification makes a few of these mandatory, but also defines - some linux-specific properties that would be normally constructed by - the prom_init() trampoline when booting with an OF client interface, - but that you have to provide yourself when using the flattened format. - - Recommended properties: - - - bootargs : This zero-terminated string is passed as the kernel - command line - - linux,stdout-path : This is the full path to your standard - console device if any. Typically, if you have serial devices on - your board, you may want to put the full path to the one set as - the default console in the firmware here, for the kernel to pick - it up as its own default console. If you look at the function - set_preferred_console() in arch/ppc64/kernel/setup.c, you'll see - that the kernel tries to find out the default console and has - knowledge of various types like 8250 serial ports. You may want - to extend this function to add your own. - - Note that u-boot creates and fills in the chosen node for platforms - that use it. - - (Note: a practice that is now obsolete was to include a property - under /chosen called interrupt-controller which had a phandle value - that pointed to the main interrupt controller) - - f) the /soc<SOCname> node - - This node is used to represent a system-on-a-chip (SOC) and must be - present if the processor is a SOC. The top-level soc node contains - information that is global to all devices on the SOC. The node name - should contain a unit address for the SOC, which is the base address - of the memory-mapped register set for the SOC. The name of an soc - node should start with "soc", and the remainder of the name should - represent the part number for the soc. For example, the MPC8540's - soc node would be called "soc8540". - - Required properties: - - - device_type : Should be "soc" - - ranges : Should be defined as specified in 1) to describe the - translation of SOC addresses for memory mapped SOC registers. - - bus-frequency: Contains the bus frequency for the SOC node. - Typically, the value of this field is filled in by the boot - loader. - - - Recommended properties: - - - reg : This property defines the address and size of the - memory-mapped registers that are used for the SOC node itself. - It does not include the child device registers - these will be - defined inside each child node. The address specified in the - "reg" property should match the unit address of the SOC node. - - #address-cells : Address representation for "soc" devices. The - format of this field may vary depending on whether or not the - device registers are memory mapped. For memory mapped - registers, this field represents the number of cells needed to - represent the address of the registers. For SOCs that do not - use MMIO, a special address format should be defined that - contains enough cells to represent the required information. - See 1) above for more details on defining #address-cells. - - #size-cells : Size representation for "soc" devices - - #interrupt-cells : Defines the width of cells used to represent - interrupts. Typically this value is <2>, which includes a - 32-bit number that represents the interrupt number, and a - 32-bit number that represents the interrupt sense and level. - This field is only needed if the SOC contains an interrupt - controller. - - The SOC node may contain child nodes for each SOC device that the - platform uses. Nodes should not be created for devices which exist - on the SOC but are not used by a particular platform. See chapter VI - for more information on how to specify devices that are part of a SOC. - - Example SOC node for the MPC8540: - - soc8540@e0000000 { - #address-cells = <1>; - #size-cells = <1>; - #interrupt-cells = <2>; - device_type = "soc"; - ranges = <00000000 e0000000 00100000> - reg = <e0000000 00003000>; - bus-frequency = <0>; - } - - - -IV - "dtc", the device tree compiler -==================================== - - -dtc source code can be found at -<http://git.jdl.com/gitweb/?p=dtc.git> - -WARNING: This version is still in early development stage; the -resulting device-tree "blobs" have not yet been validated with the -kernel. The current generated block lacks a useful reserve map (it will -be fixed to generate an empty one, it's up to the bootloader to fill -it up) among others. The error handling needs work, bugs are lurking, -etc... - -dtc basically takes a device-tree in a given format and outputs a -device-tree in another format. The currently supported formats are: - - Input formats: - ------------- - - - "dtb": "blob" format, that is a flattened device-tree block - with - header all in a binary blob. - - "dts": "source" format. This is a text file containing a - "source" for a device-tree. The format is defined later in this - chapter. - - "fs" format. This is a representation equivalent to the - output of /proc/device-tree, that is nodes are directories and - properties are files - - Output formats: - --------------- - - - "dtb": "blob" format - - "dts": "source" format - - "asm": assembly language file. This is a file that can be - sourced by gas to generate a device-tree "blob". That file can - then simply be added to your Makefile. Additionally, the - assembly file exports some symbols that can be used. - - -The syntax of the dtc tool is - - dtc [-I <input-format>] [-O <output-format>] - [-o output-filename] [-V output_version] input_filename - - -The "output_version" defines what version of the "blob" format will be -generated. Supported versions are 1,2,3 and 16. The default is -currently version 3 but that may change in the future to version 16. - -Additionally, dtc performs various sanity checks on the tree, like the -uniqueness of linux, phandle properties, validity of strings, etc... - -The format of the .dts "source" file is "C" like, supports C and C++ -style comments. - -/ { -} - -The above is the "device-tree" definition. It's the only statement -supported currently at the toplevel. - -/ { - property1 = "string_value"; /* define a property containing a 0 - * terminated string - */ - - property2 = <1234abcd>; /* define a property containing a - * numerical 32-bit value (hexadecimal) - */ - - property3 = <12345678 12345678 deadbeef>; - /* define a property containing 3 - * numerical 32-bit values (cells) in - * hexadecimal - */ - property4 = [0a 0b 0c 0d de ea ad be ef]; - /* define a property whose content is - * an arbitrary array of bytes - */ - - childnode@address { /* define a child node named "childnode" - * whose unit name is "childnode at - * address" - */ - - childprop = "hello\n"; /* define a property "childprop" of - * childnode (in this case, a string) - */ - }; -}; - -Nodes can contain other nodes etc... thus defining the hierarchical -structure of the tree. - -Strings support common escape sequences from C: "\n", "\t", "\r", -"\(octal value)", "\x(hex value)". - -It is also suggested that you pipe your source file through cpp (gcc -preprocessor) so you can use #include's, #define for constants, etc... - -Finally, various options are planned but not yet implemented, like -automatic generation of phandles, labels (exported to the asm file so -you can point to a property content and change it easily from whatever -you link the device-tree with), label or path instead of numeric value -in some cells to "point" to a node (replaced by a phandle at compile -time), export of reserve map address to the asm file, ability to -specify reserve map content at compile time, etc... - -We may provide a .h include file with common definitions of that -proves useful for some properties (like building PCI properties or -interrupt maps) though it may be better to add a notion of struct -definitions to the compiler... - - -V - Recommendations for a bootloader -==================================== - - -Here are some various ideas/recommendations that have been proposed -while all this has been defined and implemented. - - - The bootloader may want to be able to use the device-tree itself - and may want to manipulate it (to add/edit some properties, - like physical memory size or kernel arguments). At this point, 2 - choices can be made. Either the bootloader works directly on the - flattened format, or the bootloader has its own internal tree - representation with pointers (similar to the kernel one) and - re-flattens the tree when booting the kernel. The former is a bit - more difficult to edit/modify, the later requires probably a bit - more code to handle the tree structure. Note that the structure - format has been designed so it's relatively easy to "insert" - properties or nodes or delete them by just memmoving things - around. It contains no internal offsets or pointers for this - purpose. - - - An example of code for iterating nodes & retrieving properties - directly from the flattened tree format can be found in the kernel - file arch/ppc64/kernel/prom.c, look at scan_flat_dt() function, - its usage in early_init_devtree(), and the corresponding various - early_init_dt_scan_*() callbacks. That code can be re-used in a - GPL bootloader, and as the author of that code, I would be happy - to discuss possible free licensing to any vendor who wishes to - integrate all or part of this code into a non-GPL bootloader. - - - -VI - System-on-a-chip devices and nodes -======================================= - -Many companies are now starting to develop system-on-a-chip -processors, where the processor core (CPU) and many peripheral devices -exist on a single piece of silicon. For these SOCs, an SOC node -should be used that defines child nodes for the devices that make -up the SOC. While platforms are not required to use this model in -order to boot the kernel, it is highly encouraged that all SOC -implementations define as complete a flat-device-tree as possible to -describe the devices on the SOC. This will allow for the -genericization of much of the kernel code. - - -1) Defining child nodes of an SOC ---------------------------------- - -Each device that is part of an SOC may have its own node entry inside -the SOC node. For each device that is included in the SOC, the unit -address property represents the address offset for this device's -memory-mapped registers in the parent's address space. The parent's -address space is defined by the "ranges" property in the top-level soc -node. The "reg" property for each node that exists directly under the -SOC node should contain the address mapping from the child address space -to the parent SOC address space and the size of the device's -memory-mapped register file. - -For many devices that may exist inside an SOC, there are predefined -specifications for the format of the device tree node. All SOC child -nodes should follow these specifications, except where noted in this -document. - -See appendix A for an example partial SOC node definition for the -MPC8540. - - -2) Representing devices without a current OF specification ----------------------------------------------------------- - -Currently, there are many devices on SOCs that do not have a standard -representation pre-defined as part of the open firmware -specifications, mainly because the boards that contain these SOCs are -not currently booted using open firmware. This section contains -descriptions for the SOC devices for which new nodes have been -defined; this list will expand as more and more SOC-containing -platforms are moved over to use the flattened-device-tree model. - -VII - Specifying interrupt information for devices -=================================================== - -The device tree represents the busses and devices of a hardware -system in a form similar to the physical bus topology of the -hardware. - -In addition, a logical 'interrupt tree' exists which represents the -hierarchy and routing of interrupts in the hardware. - -The interrupt tree model is fully described in the -document "Open Firmware Recommended Practice: Interrupt -Mapping Version 0.9". The document is available at: -<http://playground.sun.com/1275/practice>. - -1) interrupts property ----------------------- - -Devices that generate interrupts to a single interrupt controller -should use the conventional OF representation described in the -OF interrupt mapping documentation. - -Each device which generates interrupts must have an 'interrupt' -property. The interrupt property value is an arbitrary number of -of 'interrupt specifier' values which describe the interrupt or -interrupts for the device. - -The encoding of an interrupt specifier is determined by the -interrupt domain in which the device is located in the -interrupt tree. The root of an interrupt domain specifies in -its #interrupt-cells property the number of 32-bit cells -required to encode an interrupt specifier. See the OF interrupt -mapping documentation for a detailed description of domains. - -For example, the binding for the OpenPIC interrupt controller -specifies an #interrupt-cells value of 2 to encode the interrupt -number and level/sense information. All interrupt children in an -OpenPIC interrupt domain use 2 cells per interrupt in their interrupts -property. - -The PCI bus binding specifies a #interrupt-cell value of 1 to encode -which interrupt pin (INTA,INTB,INTC,INTD) is used. - -2) interrupt-parent property ----------------------------- - -The interrupt-parent property is specified to define an explicit -link between a device node and its interrupt parent in -the interrupt tree. The value of interrupt-parent is the -phandle of the parent node. - -If the interrupt-parent property is not defined for a node, its -interrupt parent is assumed to be an ancestor in the node's -_device tree_ hierarchy. - -3) OpenPIC Interrupt Controllers --------------------------------- - -OpenPIC interrupt controllers require 2 cells to encode -interrupt information. The first cell defines the interrupt -number. The second cell defines the sense and level -information. - -Sense and level information should be encoded as follows: - - 0 = low to high edge sensitive type enabled - 1 = active low level sensitive type enabled - 2 = active high level sensitive type enabled - 3 = high to low edge sensitive type enabled - -4) ISA Interrupt Controllers ----------------------------- - -ISA PIC interrupt controllers require 2 cells to encode -interrupt information. The first cell defines the interrupt -number. The second cell defines the sense and level -information. - -ISA PIC interrupt controllers should adhere to the ISA PIC -encodings listed below: - - 0 = active low level sensitive type enabled - 1 = active high level sensitive type enabled - 2 = high to low edge sensitive type enabled - 3 = low to high edge sensitive type enabled - -VIII - Specifying Device Power Management Information (sleep property) -=================================================================== - -Devices on SOCs often have mechanisms for placing devices into low-power -states that are decoupled from the devices' own register blocks. Sometimes, -this information is more complicated than a cell-index property can -reasonably describe. Thus, each device controlled in such a manner -may contain a "sleep" property which describes these connections. - -The sleep property consists of one or more sleep resources, each of -which consists of a phandle to a sleep controller, followed by a -controller-specific sleep specifier of zero or more cells. - -The semantics of what type of low power modes are possible are defined -by the sleep controller. Some examples of the types of low power modes -that may be supported are: - - - Dynamic: The device may be disabled or enabled at any time. - - System Suspend: The device may request to be disabled or remain - awake during system suspend, but will not be disabled until then. - - Permanent: The device is disabled permanently (until the next hard - reset). - -Some devices may share a clock domain with each other, such that they should -only be suspended when none of the devices are in use. Where reasonable, -such nodes should be placed on a virtual bus, where the bus has the sleep -property. If the clock domain is shared among devices that cannot be -reasonably grouped in this manner, then create a virtual sleep controller -(similar to an interrupt nexus, except that defining a standardized -sleep-map should wait until its necessity is demonstrated). - -Appendix A - Sample SOC node for MPC8540 -======================================== - - soc@e0000000 { - #address-cells = <1>; - #size-cells = <1>; - compatible = "fsl,mpc8540-ccsr", "simple-bus"; - device_type = "soc"; - ranges = <0x00000000 0xe0000000 0x00100000> - bus-frequency = <0>; - interrupt-parent = <&pic>; - - ethernet@24000 { - #address-cells = <1>; - #size-cells = <1>; - device_type = "network"; - model = "TSEC"; - compatible = "gianfar", "simple-bus"; - reg = <0x24000 0x1000>; - local-mac-address = [ 00 E0 0C 00 73 00 ]; - interrupts = <29 2 30 2 34 2>; - phy-handle = <&phy0>; - sleep = <&pmc 00000080>; - ranges; - - mdio@24520 { - reg = <0x24520 0x20>; - compatible = "fsl,gianfar-mdio"; - - phy0: ethernet-phy@0 { - interrupts = <5 1>; - reg = <0>; - device_type = "ethernet-phy"; - }; - - phy1: ethernet-phy@1 { - interrupts = <5 1>; - reg = <1>; - device_type = "ethernet-phy"; - }; - - phy3: ethernet-phy@3 { - interrupts = <7 1>; - reg = <3>; - device_type = "ethernet-phy"; - }; - }; - }; - - ethernet@25000 { - device_type = "network"; - model = "TSEC"; - compatible = "gianfar"; - reg = <0x25000 0x1000>; - local-mac-address = [ 00 E0 0C 00 73 01 ]; - interrupts = <13 2 14 2 18 2>; - phy-handle = <&phy1>; - sleep = <&pmc 00000040>; - }; - - ethernet@26000 { - device_type = "network"; - model = "FEC"; - compatible = "gianfar"; - reg = <0x26000 0x1000>; - local-mac-address = [ 00 E0 0C 00 73 02 ]; - interrupts = <41 2>; - phy-handle = <&phy3>; - sleep = <&pmc 00000020>; - }; - - serial@4500 { - #address-cells = <1>; - #size-cells = <1>; - compatible = "fsl,mpc8540-duart", "simple-bus"; - sleep = <&pmc 00000002>; - ranges; - - serial@4500 { - device_type = "serial"; - compatible = "ns16550"; - reg = <0x4500 0x100>; - clock-frequency = <0>; - interrupts = <42 2>; - }; - - serial@4600 { - device_type = "serial"; - compatible = "ns16550"; - reg = <0x4600 0x100>; - clock-frequency = <0>; - interrupts = <42 2>; - }; - }; - - pic: pic@40000 { - interrupt-controller; - #address-cells = <0>; - #interrupt-cells = <2>; - reg = <0x40000 0x40000>; - compatible = "chrp,open-pic"; - device_type = "open-pic"; - }; - - i2c@3000 { - interrupts = <43 2>; - reg = <0x3000 0x100>; - compatible = "fsl-i2c"; - dfsrr; - sleep = <&pmc 00000004>; - }; - - pmc: power@e0070 { - compatible = "fsl,mpc8540-pmc", "fsl,mpc8548-pmc"; - reg = <0xe0070 0x20>; - }; - }; |