x86: Disable DAC on VIA bridges

Several reports that VIA bridges don't support DAC and corrupt
data.  I don't know if it's fixed, but let's just blacklist
them all for now.

It can be overwritten with iommu=usedac

Signed-off-by: Andi Kleen <ak@suse.de>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 12 insertions, 0 deletions

diff --git a/arch/x86_64/kernel/pci-dma.c b/arch/x86_64/kernel/pci-dma.c
index 651ccfb0669..9f80aad3fe2 100644
--- a/arch/x86_64/kernel/pci-dma.c
+++ b/arch/x86_64/kernel/pci-dma.c
@@ -322,5 +322,17 @@ static int __init pci_iommu_init(void)
         return 0;
 }
 
+#ifdef CONFIG_PCI
+/* Many VIA bridges seem to corrupt data for DAC. Disable it here */
+
+static __devinit void via_no_dac(struct pci_dev *dev)
+{
+        if ((dev->class >> 8) == PCI_CLASS_BRIDGE_PCI && forbid_dac == 0) {
+                printk(KERN_INFO "PCI: VIA PCI bridge detected. Disabling DAC.\n");
+                forbid_dac = 1;
+        }
+}
+DECLARE_PCI_FIXUP_FINAL(PCI_VENDOR_ID_VIA, PCI_ANY_ID, via_no_dac);
+#endif
 /* Must execute after PCI subsystem */
 fs_initcall(pci_iommu_init);