x86: usb debug port early console, v4

based on work from Eric, and add some timeout so don't dead loop when debug
device is not installed

v2: fix checkpatch warning
v3: move ehci struct def to linux/usrb/ehci_def.h from host/ehci.h
    also add CONFIG_EARLY_PRINTK_DBGP to disable it by default
v4: address comments from Ingo, seperate ehci reg def moving to another patch
    also add auto detect port that connect to debug device for Nvidia
    southbridge

Signed-off-by: Yinghai Lu <yhlu.kernel@gmail.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Andi Kleen <andi@firstfloor.org>
Cc: "Arjan van de Ven" <arjan@infradead.org>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: "Greg KH" <greg@kroah.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 2 insertions, 1 deletions

diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index e7bea3e85304..92ddd4afe174 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -657,11 +657,12 @@ and is between 256 and 4096 characters. It is defined in the file
         earlyprintk=    [X86-32,X86-64,SH,BLACKFIN]
                         earlyprintk=vga
                         earlyprintk=serial[,ttySn[,baudrate]]
+                        earlyprintk=dbgp
 
                         Append ",keep" to not disable it when the real console
                         takes over.
 
-                        Only vga or serial at a time, not both.
+                        Only vga or serial or usb debug port at a time.
 
                         Currently only ttyS0 and ttyS1 are supported.