[PATCH] vesafb: Document mtrr boot option usage

["Antonino A. Daplas" <adaplas@gmail.com>]

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

    From: Antonino Daplas <adaplas@pol.net>
    Signed-off-by: Antonino Daplas <adaplas@pol.net>
---

 vesafb.txt |   16 +++++++++++++++-
 1 files changed, 15 insertions(+), 1 deletion(-)

--- a/Documentation/fb/vesafb.txt
+++ b/Documentation/fb/vesafb.txt
@@ -144,7 +144,21 @@ vgapal	Use the standard vga registers fo
 	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


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