2 files changed, 20 insertions, 0 deletions

diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index fe3031d56431..5d171b7b8393 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -1092,6 +1092,11 @@ 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 3960ab7e1497..219f86eb6123 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