partitions/efi: complete documentation of gpt kernel param purpose

The usage of the 'gpt' kernel parameter is twofold: (i) skip any mbr
integrity checks and (ii) enable the backup GPT header to be used in
situations where the primary one is corrupted.  This last "feature" is not
obvious and needs to be properly documented in the kernel-parameters
document.

Addresses https://bugzilla.kernel.org/show_bug.cgi?id=63591

Signed-off-by: Davidlohr Bueso <davidlohr@hp.com>
Cc: Matt Domsch <Matt_Domsch@dell.com>
Cc: Matt Fleming <matt.fleming@intel.com>
Cc: "Chandramouleeswaran,Aswin" <aswin@hp.com>
Cc: Chris Murphy <bugzilla@colorremedies.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index 5efebfd1cfdf7edbf3a7b963633e50120a0c4b5c..248fe9da0b26f06f4d002896f8d0847a7097fc4c 100644 (file)
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -1043,7 +1043,9 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
                        debugfs files are removed at module unload time.
 
        gpt             [EFI] Forces disk with valid GPT signature but
-                       invalid Protective MBR to be treated as GPT.
+                       invalid Protective MBR to be treated as GPT. If the
+                       primary GPT is corrupted, it enables the backup/alternate
+                       GPT to be used instead.
 
        grcan.enable0=  [HW] Configuration of physical interface 0. Determines
                        the "Enable 0" bit of the configuration register.