Document powerpc udbg-immortal

Back in 2006 the "udbg-immortal" kernel option has been introduced:

  > commit 3b5e905ee3bd23e9311951890aba57a0dbc81ca4
  > Author: Benjamin Herrenschmidt <benh@au1.ibm.com>
  > Date:   Wed Jun 7 12:06:20 2006 +1000
  >
  >  [PATCH] powerpc: Add udbg-immortal kernel option

...but I could not find it documented anywhere in the sources.
This patch adds it to Documentation/kernel-parameters.txt.

Signed-off-by: Christian Kujau <lists@nerdbynature.de>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

1 files changed, 5 insertions, 0 deletions

diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index fd248a318211..960c32138ccb 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -2524,6 +2524,11 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
                         <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7>
                         See also Documentation/input/joystick-parport.txt
 
+        udbg-immortal   [PPC] When debugging early kernel crashes that
+                        happen after console_init() and before a proper 
+                        console driver takes over, this boot options might
+                        help "seeing" what's going on.
+
         uhash_entries=  [KNL,NET]
                         Set number of hash buckets for UDP/UDP-Lite connections