x86: EFI runtime service support: document for EFI runtime services

This patch adds document for EFI x86_64 runtime services support.

Signed-off-by: Chandramouli Narayanan <mouli@linux.intel.com>
Signed-off-by: Huang Ying <ying.huang@intel.com>
Cc: Andi Kleen <ak@suse.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

1 files changed, 9 insertions, 0 deletions

diff --git a/Documentation/x86_64/uefi.txt b/Documentation/x86_64/uefi.txt
index 91a98edfb588..7d77120a5184 100644
--- a/Documentation/x86_64/uefi.txt
+++ b/Documentation/x86_64/uefi.txt
@@ -19,6 +19,10 @@ Mechanics:
 - Build the kernel with the following configuration.
         CONFIG_FB_EFI=y
         CONFIG_FRAMEBUFFER_CONSOLE=y
+  If EFI runtime services are expected, the following configuration should
+  be selected.
+        CONFIG_EFI=y
+        CONFIG_EFI_VARS=y or m          # optional
 - Create a VFAT partition on the disk
 - Copy the following to the VFAT partition:
         elilo bootloader with x86_64 support, elilo configuration file,
@@ -27,3 +31,8 @@ Mechanics:
         can be found in the elilo sourceforge project.
 - Boot to EFI shell and invoke elilo choosing the kernel image built
   in first step.
+- If some or all EFI runtime services don't work, you can try following
+  kernel command line parameters to turn off some or all EFI runtime
+  services.
+        noefi           turn off all EFI runtime services
+        reboot_type=k   turn off EFI reboot runtime service