[PATCH] vesafb: Document mtrr boot option usage

Document mtrr boot option usage to Documentation/fb/vesafb.txt.

Signed-off-by: Antonino Daplas <adaplas@pol.net>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 15 insertions, 1 deletions

diff --git a/Documentation/fb/vesafb.txt b/Documentation/fb/vesafb.txt
index 814e2f56a6ad..62db6758d1c1 100644
--- a/Documentation/fb/vesafb.txt
+++ b/Documentation/fb/vesafb.txt
@@ -144,7 +144,21 @@ vgapal	Use the standard vga registers for palette changes.
         This is the default.
 pmipal  Use the protected mode interface for palette changes.
 
-mtrr    setup memory type range registers for the vesafb framebuffer.
+mtrr:n  setup memory type range registers for the vesafb framebuffer
+        where n:
+              0 - disabled (equivalent to nomtrr)
+              1 - uncachable
+              2 - write-back
+              3 - write-combining (default)
+              4 - write-through
+
+        If you see the following in dmesg, choose the type that matches the
+        old one. In this example, use "mtrr:2".
+...
+mtrr: type mismatch for e0000000,8000000 old: write-back new: write-combining
+...
+
+nomtrr  disable mtrr
 
 vremap:n
         remap 'n' MiB of video RAM. If 0 or not specified, remap memory