[PATCH] via vt8237 apic bypass deassertion quirk

The VIA VT8237's IOAPIC sends 'APIC De-Assert Messages' by default, causing
another CPU interrupt when the IRQ pin is de-asserted.  This feature is
switched off by the patch to get rid of doubled ioapic level interrupt
rates.

Signed-off-by: Karsten Wiese <annabellesgarden@yahoo.de>
Tested-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

diff --git a/drivers/pci/quirks.c b/drivers/pci/quirks.c
index bb36bb6..140354a 100644 (file)
--- a/drivers/pci/quirks.c
+++ b/drivers/pci/quirks.c
@@ -421,6 +421,25 @@ static void __devinit quirk_via_ioapic(struct pci_dev *dev)
 }
 DECLARE_PCI_FIXUP_FINAL(PCI_VENDOR_ID_VIA,     PCI_DEVICE_ID_VIA_82C686,       quirk_via_ioapic );
 
+/*
+ * VIA 8237: Some BIOSs don't set the 'Bypass APIC De-Assert Message' Bit.
+ * This leads to doubled level interrupt rates.
+ * Set this bit to get rid of cycle wastage.
+ * Otherwise uncritical.
+ */
+static void __devinit quirk_via_vt8237_bypass_apic_deassert(struct pci_dev *dev)
+{
+       u8 misc_control2;
+#define BYPASS_APIC_DEASSERT 8
+
+       pci_read_config_byte(dev, 0x5B, &misc_control2);
+       if (!(misc_control2 & BYPASS_APIC_DEASSERT)) {
+               printk(KERN_INFO "PCI: Bypassing VIA 8237 APIC De-Assert Message\n");
+               pci_write_config_byte(dev, 0x5B, misc_control2|BYPASS_APIC_DEASSERT);
+       }
+}
+DECLARE_PCI_FIXUP_FINAL(PCI_VENDOR_ID_VIA,     PCI_DEVICE_ID_VIA_8237,         quirk_via_vt8237_bypass_apic_deassert);
+
 /*
  * The AMD io apic can hang the box when an apic irq is masked.
  * We check all revs >= B0 (yet not in the pre production!) as the bug