forked from Minki/linux
a1aade4788
[ mingo: small edits and extensions. ] Signed-off-by: Yinghai Lu <yinghai@kernel.org> Cc: "Eric W. Biederman" <ebiederm@xmission.com> Cc: Greg KH <gregkh@suse.de> Cc: Randy Dunlap <randy.dunlap@oracle.com> Cc: Alan Stern <stern@rowland.harvard.edu> Cc: Sarah Sharp <sarah.a.sharp@intel.com> Cc: Andrew Morton <akpm@linux-foundation.org> LKML-Reference: <49AF18B7.4050305@kernel.org> Signed-off-by: Ingo Molnar <mingo@elte.hu>
102 lines
3.9 KiB
Plaintext
102 lines
3.9 KiB
Plaintext
|
|
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:
|
|
|
|
[host/target] <-------> [USB debug key] <-------> [client/console]
|
|
|
|
1. There are three 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
|
|
^^^^^^^^^^^ <==================== [ HERE ]
|
|
Kernel driver in use: ehci_hcd
|
|
Kernel modules: ehci-hcd
|
|
...
|
|
|
|
( If your system does not list a debug port capability then you probably
|
|
wont 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.) Thirdly, you need a second client/console system with a regular USB port.
|
|
|
|
2. 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".
|
|
(If you are using Grub, append it to the 'kernel' line in
|
|
/etc/grub.conf)
|
|
|
|
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 debug device connected.
|
|
|
|
3. Testing that it works fine:
|
|
|
|
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.
|