[tip:x86/urgent] doc, xen: Mention 'earlyprintk=xen' in the documentation.

[tip-bot for Konrad Rzeszutek Wilk]

Commit-ID:  2482a92e7d17187301d7313cfe5021b13393a0b4
Gitweb:     http://git.kernel.org/tip/2482a92e7d17187301d7313cfe5021b13393a0b4
Author:     Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
AuthorDate: Mon, 25 Feb 2013 15:54:08 -0500
Committer:  H. Peter Anvin <hpa@xxxxxxxxxxxxxxx>
CommitDate: Mon, 25 Feb 2013 13:41:18 -0800

doc, xen: Mention 'earlyprintk=xen' in the documentation.

The earlyprintk for Xen PV guests utilizes a simple hypercall
(console_io) to provide output to Xen emergency console.

Note that the Xen hypervisor should be booted with 'loglevel=all'
to output said information.

Reported-by: H. Peter Anvin <hpa@xxxxxxxxx>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
Link: http://lkml.kernel.org/r/1361825650-14031-2-git-send-email-konrad.wilk@xxxxxxxxxx
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: H. Peter Anvin <hpa@xxxxxxxxxxxxxxx>
---
 Documentation/kernel-parameters.txt | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index 6c72381..c4cc199 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -754,6 +754,7 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
 
 	earlyprintk=	[X86,SH,BLACKFIN]
 			earlyprintk=vga
+			earlyprintk=xen
 			earlyprintk=serial[,ttySn[,baudrate]]
 			earlyprintk=ttySn[,baudrate]
 			earlyprintk=dbgp[debugController#]
@@ -771,6 +772,8 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
 			The VGA output is eventually overwritten by the real
 			console.
 
+			The xen output can only be used by Xen PV guests.
+
 	ekgdboc=	[X86,KGDB] Allow early kernel console debugging
 			ekgdboc=kbd
 
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