[PATCH] x86_64: Add option to disable timer check

This works around the too fast timer seen on some ATI boards.

I don't feel confident enough about it yet to enable it by default, but give
users the option.

Patch and debugging from Christopher Allen Wing <wingc@engin.umich.edu>, with
minor tweaks (renamed the option and documented it)

Signed-off-by: Andi Kleen <ak@suse.de>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

2 files changed, 13 insertions, 1 deletions

diff --git a/Documentation/x86_64/boot-options.txt b/Documentation/x86_64/boot-options.txt
index 44b6eea60ece..b9e6be00cadf 100644
--- a/Documentation/x86_64/boot-options.txt
+++ b/Documentation/x86_64/boot-options.txt
@@ -25,6 +25,9 @@ APICs
 
    noapictimer   Don't set up the APIC timer
 
+   no_timer_check Don't check the IO-APIC timer. This can work around
+                 problems with incorrect timer initialization on some boards.
+
 Early Console
 
    syntax: earlyprintk=vga
diff --git a/arch/x86_64/kernel/io_apic.c b/arch/x86_64/kernel/io_apic.c
index ac7684324954..80e9b498c443 100644
--- a/arch/x86_64/kernel/io_apic.c
+++ b/arch/x86_64/kernel/io_apic.c
@@ -42,6 +42,8 @@
 
 int sis_apic_bug; /* not actually supported, dummy for compile */
 
+static int no_timer_check;
+
 static DEFINE_SPINLOCK(ioapic_lock);
 
 /*
@@ -1601,7 +1603,7 @@ static inline void check_timer(void)
                  * Ok, does IRQ0 through the IOAPIC work?
                  */
                 unmask_IO_APIC_irq(0);
-                if (timer_irq_works()) {
+                if (!no_timer_check && timer_irq_works()) {
                         nmi_watchdog_default();
                         if (nmi_watchdog == NMI_IO_APIC) {
                                 disable_8259A_irq(0);
@@ -1671,6 +1673,13 @@ static inline void check_timer(void)
         panic("IO-APIC + timer doesn't work! Try using the 'noapic' kernel parameter\n");
 }
 
+static int __init notimercheck(char *s)
+{
+        no_timer_check = 1;
+        return 1;
+}
+__setup("no_timer_check", notimercheck);
+
 /*
  *
  * IRQ's that are handled by the PIC in the MPS IOAPIC case.