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diff --git a/Documentation/x86/earlyprintk.rst b/Documentation/x86/earlyprintk.rst deleted file mode 100644 index 51ef11e8f725..000000000000 --- a/Documentation/x86/earlyprintk.rst +++ /dev/null @@ -1,151 +0,0 @@ -.. 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 -two USB cables, connected like this:: - - [host/target] <-------> [USB debug key] <-------> [client/console] - -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 - ... - - .. 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: - - 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. - - 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 - port and the NetChip device will only work as an early printk - device in this port. The EHCI host controllers are electrically - wired such that the EHCI debug controller is hooked up to the - first physical port and there is no way to change this via software. - You can find the physical port through experimentation by trying - each physical port on the system and rebooting. Or you can try - and use lsusb or look at the kernel info messages emitted by the - usb stack when you plug a usb device into various ports on the - "host/target" system. - - Some hardware vendors do not expose the usb debug port with a - physical connector and if you find such a device send a complaint - 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 - 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. - -Software requirements -===================== - - a) On the host/target system: - - 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". - - .. 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 - comes from the PCI bus enumeration of the EHCI controllers. The - default with no number argument is "0" or the first EHCI debug - 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. - - b) On the client/console system: - - You should enable the following kernel config option:: - - CONFIG_USB_SERIAL_DEBUG=y - - On the next bootup with the modified kernel you should - get a /dev/ttyUSBx device(s). - - Now this channel of kernel messages is ready to be used: start - your favorite terminal emulator (minicom, etc.) and set - 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 - and find out which port has a debug device connected. - -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:: - - echo h > /proc/sysrq-trigger - -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:: - - cat /dev/ttyUSB0 - -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. |