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>
diff --git a/include/asm-i386/dma-mapping.h b/include/asm-i386/dma-mapping.h
index 183eebe..f1d72d1 100644
--- a/include/asm-i386/dma-mapping.h
+++ b/include/asm-i386/dma-mapping.h
@@ -123,6 +123,8 @@
return 0;
}
+extern int forbid_dac;
+
static inline int
dma_supported(struct device *dev, u64 mask)
{
@@ -134,6 +136,10 @@
if(mask < 0x00ffffff)
return 0;
+ /* Work around chipset bugs */
+ if (forbid_dac > 0 && mask > 0xffffffffULL)
+ return 0;
+
return 1;
}