diff options
Diffstat (limited to 'Documentation/x86')
| -rw-r--r-- | Documentation/x86/earlyprintk.rst (renamed from Documentation/x86/earlyprintk.txt) | 122 | ||||
| -rw-r--r-- | Documentation/x86/index.rst | 1 |
2 files changed, 67 insertions, 56 deletions
diff --git a/Documentation/x86/earlyprintk.txt b/Documentation/x86/earlyprintk.rst index 46933e06c972..11307378acf0 100644 --- a/Documentation/x86/earlyprintk.txt +++ b/Documentation/x86/earlyprintk.rst @@ -1,52 +1,58 @@ +.. SPDX-License-Identifier: GPL-2.0 + +============ +Early Printk +============ Mini-HOWTO for using the earlyprintk=dbgp boot option with a USB2 Debug port key and a debug cable, on x86 systems. You need two computers, the 'USB debug key' special gadget and -and two USB cables, connected like this: +and two USB cables, connected like this:: [host/target] <-------> [USB debug key] <-------> [client/console] -1. There are a number of specific hardware requirements: - - a.) Host/target system needs to have USB debug port capability. - - You can check this capability by looking at a 'Debug port' bit in - the lspci -vvv output: - - # lspci -vvv - ... - 00:1d.7 USB Controller: Intel Corporation 82801H (ICH8 Family) USB2 EHCI Controller #1 (rev 03) (prog-if 20 [EHCI]) - Subsystem: Lenovo ThinkPad T61 - Control: I/O- Mem+ BusMaster+ SpecCycle- MemWINV- VGASnoop- ParErr- Stepping- SERR+ FastB2B- DisINTx- - Status: Cap+ 66MHz- UDF- FastB2B+ ParErr- DEVSEL=medium >TAbort- <TAbort- <MAbort- >SERR- <PERR- INTx- - Latency: 0 - Interrupt: pin D routed to IRQ 19 - Region 0: Memory at fe227000 (32-bit, non-prefetchable) [size=1K] - Capabilities: [50] Power Management version 2 - Flags: PMEClk- DSI- D1- D2- AuxCurrent=375mA PME(D0+,D1-,D2-,D3hot+,D3cold+) - Status: D0 PME-Enable- DSel=0 DScale=0 PME+ - Capabilities: [58] Debug port: BAR=1 offset=00a0 +Hardware requirements +===================== + + a) Host/target system needs to have USB debug port capability. + + You can check this capability by looking at a 'Debug port' bit in + the lspci -vvv output:: + + # lspci -vvv + ... + 00:1d.7 USB Controller: Intel Corporation 82801H (ICH8 Family) USB2 EHCI Controller #1 (rev 03) (prog-if 20 [EHCI]) + Subsystem: Lenovo ThinkPad T61 + Control: I/O- Mem+ BusMaster+ SpecCycle- MemWINV- VGASnoop- ParErr- Stepping- SERR+ FastB2B- DisINTx- + Status: Cap+ 66MHz- UDF- FastB2B+ ParErr- DEVSEL=medium >TAbort- <TAbort- <MAbort- >SERR- <PERR- INTx- + Latency: 0 + Interrupt: pin D routed to IRQ 19 + Region 0: Memory at fe227000 (32-bit, non-prefetchable) [size=1K] + Capabilities: [50] Power Management version 2 + Flags: PMEClk- DSI- D1- D2- AuxCurrent=375mA PME(D0+,D1-,D2-,D3hot+,D3cold+) + Status: D0 PME-Enable- DSel=0 DScale=0 PME+ + Capabilities: [58] Debug port: BAR=1 offset=00a0 ^^^^^^^^^^^ <==================== [ HERE ] - Kernel driver in use: ehci_hcd - Kernel modules: ehci-hcd - ... + Kernel driver in use: ehci_hcd + Kernel modules: ehci-hcd + ... -( If your system does not list a debug port capability then you probably - won't be able to use the USB debug key. ) + .. note:: + If your system does not list a debug port capability then you probably + won't be able to use the USB debug key. - b.) You also need a NetChip USB debug cable/key: + b) You also need a NetChip USB debug cable/key: http://www.plxtech.com/products/NET2000/NET20DC/default.asp This is a small blue plastic connector with two USB connections; it draws power from its USB connections. - c.) You need a second client/console system with a high speed USB 2.0 - port. + c) You need a second client/console system with a high speed USB 2.0 port. - d.) The NetChip device must be plugged directly into the physical - debug port on the "host/target" system. You cannot use a USB hub in + d) The NetChip device must be plugged directly into the physical + debug port on the "host/target" system. You cannot use a USB hub in between the physical debug port and the "host/target" system. The EHCI debug controller is bound to a specific physical USB @@ -65,29 +71,31 @@ and two USB cables, connected like this: to the hardware vendor, because there is no reason not to wire this port into one of the physically accessible ports. - e.) It is also important to note, that many versions of the NetChip + e) It is also important to note, that many versions of the NetChip device require the "client/console" system to be plugged into the right hand side of the device (with the product logo facing up and readable left to right). The reason being is that the 5 volt power supply is taken from only one side of the device and it must be the side that does not get rebooted. -2. Software requirements: +Software requirements +===================== - a.) On the host/target system: + a) On the host/target system: - You need to enable the following kernel config option: + You need to enable the following kernel config option:: CONFIG_EARLY_PRINTK_DBGP=y And you need to add the boot command line: "earlyprintk=dbgp". - (If you are using Grub, append it to the 'kernel' line in - /etc/grub.conf. If you are using Grub2 on a BIOS firmware system, - append it to the 'linux' line in /boot/grub2/grub.cfg. If you are - using Grub2 on an EFI firmware system, append it to the 'linux' - or 'linuxefi' line in /boot/grub2/grub.cfg or - /boot/efi/EFI/<distro>/grub.cfg.) + .. note:: + If you are using Grub, append it to the 'kernel' line in + /etc/grub.conf. If you are using Grub2 on a BIOS firmware system, + append it to the 'linux' line in /boot/grub2/grub.cfg. If you are + using Grub2 on an EFI firmware system, append it to the 'linux' + or 'linuxefi' line in /boot/grub2/grub.cfg or + /boot/efi/EFI/<distro>/grub.cfg. On systems with more than one EHCI debug controller you must specify the correct EHCI debug controller number. The ordering @@ -96,14 +104,15 @@ and two USB cables, connected like this: controller. To use the second EHCI debug controller, you would use the command line: "earlyprintk=dbgp1" - NOTE: normally earlyprintk console gets turned off once the - regular console is alive - use "earlyprintk=dbgp,keep" to keep - this channel open beyond early bootup. This can be useful for - debugging crashes under Xorg, etc. + .. note:: + normally earlyprintk console gets turned off once the + regular console is alive - use "earlyprintk=dbgp,keep" to keep + this channel open beyond early bootup. This can be useful for + debugging crashes under Xorg, etc. - b.) On the client/console system: + b) On the client/console system: - You should enable the following kernel config option: + You should enable the following kernel config option:: CONFIG_USB_SERIAL_DEBUG=y @@ -115,27 +124,28 @@ and two USB cables, connected like this: it up to use /dev/ttyUSB0 - or use a raw 'cat /dev/ttyUSBx' to see the raw output. - c.) On Nvidia Southbridge based systems: the kernel will try to probe + c) On Nvidia Southbridge based systems: the kernel will try to probe and find out which port has a debug device connected. -3. Testing that it works fine: +Testing +======= - You can test the output by using earlyprintk=dbgp,keep and provoking - kernel messages on the host/target system. You can provoke a harmless - kernel message by for example doing: +You can test the output by using earlyprintk=dbgp,keep and provoking +kernel messages on the host/target system. You can provoke a harmless +kernel message by for example doing:: echo h > /proc/sysrq-trigger - On the host/target system you should see this help line in "dmesg" output: +On the host/target system you should see this help line in "dmesg" output:: SysRq : HELP : loglevel(0-9) reBoot Crashdump terminate-all-tasks(E) memory-full-oom-kill(F) kill-all-tasks(I) saK show-backtrace-all-active-cpus(L) show-memory-usage(M) nice-all-RT-tasks(N) powerOff show-registers(P) show-all-timers(Q) unRaw Sync show-task-states(T) Unmount show-blocked-tasks(W) dump-ftrace-buffer(Z) - On the client/console system do: +On the client/console system do:: cat /dev/ttyUSB0 - And you should see the help line above displayed shortly after you've - provoked it on the host system. +And you should see the help line above displayed shortly after you've +provoked it on the host system. If it does not work then please ask about it on the linux-kernel@vger.kernel.org mailing list or contact the x86 maintainers. diff --git a/Documentation/x86/index.rst b/Documentation/x86/index.rst index 0e3e73458738..d9ccc0f39279 100644 --- a/Documentation/x86/index.rst +++ b/Documentation/x86/index.rst @@ -13,3 +13,4 @@ x86-specific Documentation exception-tables kernel-stacks entry_64 + earlyprintk |