path: root/Documentation/x86
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authorJason Wessel <jason.wessel@windriver.com>2009-08-20 15:39:57 -0500
committerGreg Kroah-Hartman <gregkh@suse.de>2009-09-23 06:46:39 -0700
commit9780bc41dca728f9b082a42d9e1f1716d5057081 (patch)
tree5f426d8a739176c4c89915cdb221dabc5ed0da10 /Documentation/x86
parent68d2956a810b5c1b8213a1a9f59eacc54d7ce087 (diff)
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>
Diffstat (limited to 'Documentation/x86')
1 files changed, 37 insertions, 2 deletions
diff --git a/Documentation/x86/earlyprintk.txt b/Documentation/x86/earlyprintk.txt
index 607b1a016064..f19802c0f485 100644
--- a/Documentation/x86/earlyprintk.txt
+++ b/Documentation/x86/earlyprintk.txt
@@ -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
+ 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

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