[PATCH] x86_64: avoid IRQ0 ioapic pin collision

The patch addresses a problem with ACPI SCI interrupt entry, which gets
re-used, and the IRQ is assigned to another unrelated device.  The patch
corrects the code such that SCI IRQ is skipped and duplicate entry is
avoided.  Second issue came up with VIA chipset, the problem was caused by
original patch assigning IRQs starting 16 and up.  The VIA chipset uses
4-bit IRQ register for internal interrupt routing, and therefore cannot
handle IRQ numbers assigned to its devices.  The patch corrects this
problem by allowing PCI IRQs below 16.

Cc: len.brown@intel.com

Signed-off by: Natalie Protasevich <Natalie.Protasevich@unisys.com>
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, 16 insertions, 1 deletions

diff --git a/arch/i386/kernel/io_apic.c b/arch/i386/kernel/io_apic.c
index f8f132aa5472..d70f2ade5cde 100644
--- a/arch/i386/kernel/io_apic.c
+++ b/arch/i386/kernel/io_apic.c
@@ -2238,6 +2238,8 @@ static inline void unlock_ExtINT_logic(void)
         spin_unlock_irqrestore(&ioapic_lock, flags);
 }
 
+int timer_uses_ioapic_pin_0;
+
 /*
  * This code may look a bit paranoid, but it's supposed to cooperate with
  * a wide range of boards and BIOS bugs.  Fortunately only the timer IRQ
@@ -2274,6 +2276,9 @@ static inline void check_timer(void)
         pin2  = ioapic_i8259.pin;
         apic2 = ioapic_i8259.apic;
 
+        if (pin1 == 0)
+                timer_uses_ioapic_pin_0 = 1;
+
         printk(KERN_INFO "..TIMER: vector=0x%02X apic1=%d pin1=%d apic2=%d pin2=%d\n",
                 vector, apic1, pin1, apic2, pin2);
 
diff --git a/arch/i386/kernel/mpparse.c b/arch/i386/kernel/mpparse.c
index 34d21e21e012..6b1392d33ed5 100644
--- a/arch/i386/kernel/mpparse.c
+++ b/arch/i386/kernel/mpparse.c
@@ -1130,7 +1130,17 @@ int mp_register_gsi (u32 gsi, int triggering, int polarity)
                  */
                 int irq = gsi;
                 if (gsi < MAX_GSI_NUM) {
-                        if (gsi > 15)
+                        /*
+                         * Retain the VIA chipset work-around (gsi > 15), but
+                         * avoid a problem where the 8254 timer (IRQ0) is setup
+                         * via an override (so it's not on pin 0 of the ioapic),
+                         * and at the same time, the pin 0 interrupt is a PCI
+                         * type.  The gsi > 15 test could cause these two pins
+                         * to be shared as IRQ0, and they are not shareable.
+                         * So test for this condition, and if necessary, avoid
+                         * the pin collision.
+                         */
+                        if (gsi > 15 || (gsi == 0 && !timer_uses_ioapic_pin_0))
                                 gsi = pci_irq++;
                         /*
                          * Don't assign IRQ used by ACPI SCI