[PATCH 2/2] x86: GEODE add the "mfgptfix" boot time option to fix MFGPT timers

[Willy Tarreau <w@1wt.eu>]

The new "mfgptfix" boot command line option may be usd to fix MFGPT
timers on AMD Geode platforms when the BIOS has incorrectly applied
a workaround. TinyBIOS version 0.98 is known to be affected, 0.99
fixes the problem by letting the user disable the workaround.

Signed-off-by: Willy Tarreau <w@1wt.eu>
---
 Documentation/kernel-parameters.txt |    5 +++++
 arch/x86/kernel/mfgpt_32.c          |   15 +++++++++++++++
 2 files changed, 20 insertions(+), 0 deletions(-)

diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index c417877..83c6704 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -1051,6 +1051,11 @@ and is between 256 and 4096 characters. It is defined in the file
 			Multi-Function General Purpose Timers on AMD Geode
 			platforms.
 
+	mfgptfix	[X86-32] Fix MFGPT timers on AMD Geode platforms when
+			the BIOS has incorrectly applied a workaround. TinyBIOS
+			version 0.98 is known to be affected, 0.99 fixes the
+			problem by letting the user disable the workaround.
+
 	mga=		[HW,DRM]
 
 	mousedev.tap_time=
diff --git a/arch/x86/kernel/mfgpt_32.c b/arch/x86/kernel/mfgpt_32.c
index 5519091..f38d4a9 100644
--- a/arch/x86/kernel/mfgpt_32.c
+++ b/arch/x86/kernel/mfgpt_32.c
@@ -63,6 +63,21 @@ static int __init mfgpt_disable(char *s)
 }
 __setup("nomfgpt", mfgpt_disable);
 
+/* Reset the MFGPT timers. This is required by some broken BIOSes which already
+ * do the same and leave the system in an unstable state. TinyBIOS 0.98 is
+ * affected at least (0.99 is OK with MFGPT workaround left to off).
+ */
+static int __init mfgpt_fix(char *s)
+{
+	u32 val, dummy;
+
+	/* The following udocumented bit resets the MFGPT timers */
+	val = 0xFF; dummy = 0;
+	wrmsr(0x5140002B, val, dummy);
+	return 1;
+}
+__setup("mfgptfix", mfgpt_fix);
+
 /*
  * Check whether any MFGPTs are available for the kernel to use.  In most
  * cases, firmware that uses AMD's VSA code will claim all timers during
-- 
1.5.3.4