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USB: ehci-dbgp,documentation: Documentation updates for ehci-dbgp 

Add missing information about requirements of using the EHCI usb debug
controller as well as to mention you can use a debug controller other
than the first one in the system.

Signed-off-by: Jason Wessel <jason.wessel@windriver.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Yinghai Lu <yinghai@kernel.org>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Alan Stern <stern@rowland.harvard.edu>
Cc: Sarah Sharp <sarah.a.sharp@intel.com>
Cc: Randy Dunlap <randy.dunlap@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
hifive-unleashed-5.1
Jason Wessel 2009-08-20 15:39:57 -05:00 committed by Greg Kroah-Hartman
parent 68d2956a81
commit 9780bc41dc
2 changed files with 38 additions and 3 deletions
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2
Documentation/kernel-parameters.txt
View File

@ -671,7 +671,7 @@ and is between 256 and 4096 characters. It is defined in the file
earlyprintk= [X86,SH,BLACKFIN]
earlyprintk=vga
earlyprintk=serial[,ttySn[,baudrate]]
earlyprintk=dbgp
earlyprintk=dbgp[debugController#]
Append ",keep" to not disable it when the real console
takes over.

39
Documentation/x86/earlyprintk.txt
View File

@ -7,7 +7,7 @@ and two USB cables, connected like this:
[host/target] <-------> [USB debug key] <-------> [client/console]
1. There are three specific hardware requirements:
1. There are a number of specific hardware requirements:
a.) Host/target system needs to have USB debug port capability.
@ -42,7 +42,35 @@ and two USB cables, connected like this:
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.
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 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 and 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:
@ -56,6 +84,13 @@ and two USB cables, connected like this:
(If you are using Grub, append it to the 'kernel' line in
/etc/grub.conf)
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" 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