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Subject[PATCH for 2.6.22] [4/10] x86: Disable DAC on VIA bridges
Date

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>

---
arch/i386/kernel/pci-dma.c | 27 +++++++++++++++++++++++++++
arch/x86_64/kernel/pci-dma.c | 12 ++++++++++++
include/asm-i386/dma-mapping.h | 6 ++++++
3 files changed, 45 insertions(+)
Index: linux/arch/x86_64/kernel/pci-dma.c
===================================================================
--- linux.orig/arch/x86_64/kernel/pci-dma.c
+++ linux/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);
Index: linux/arch/i386/kernel/pci-dma.c
===================================================================
--- linux.orig/arch/i386/kernel/pci-dma.c
+++ linux/arch/i386/kernel/pci-dma.c
@@ -12,6 +12,7 @@
#include <linux/string.h>
#include <linux/pci.h>
#include <linux/module.h>
+#include <linux/pci.h>
#include <asm/io.h>

struct dma_coherent_mem {
@@ -148,3 +149,29 @@ void *dma_mark_declared_memory_occupied(
return mem->virt_base + (pos << PAGE_SHIFT);
}
EXPORT_SYMBOL(dma_mark_declared_memory_occupied);
+
+#ifdef CONFIG_PCI
+/* Many VIA bridges seem to corrupt data for DAC. Disable it here */
+
+int forbid_dac;
+EXPORT_SYMBOL(forbid_dac);
+
+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);
+
+static int check_iommu(char *s)
+{
+ if (!strcmp(s, "usedac")) {
+ forbid_dac = -1;
+ return 1;
+ }
+ return 0;
+}
+__setup("iommu=", check_iommu);
+#endif
Index: linux/include/asm-i386/dma-mapping.h
===================================================================
--- linux.orig/include/asm-i386/dma-mapping.h
+++ linux/include/asm-i386/dma-mapping.h
@@ -123,6 +123,8 @@ dma_mapping_error(dma_addr_t dma_addr)
return 0;
}

+extern int forbid_dac;
+
static inline int
dma_supported(struct device *dev, u64 mask)
{
@@ -134,6 +136,10 @@ dma_supported(struct device *dev, u64 ma
if(mask < 0x00ffffff)
return 0;

+ /* Work around chipset bugs */
+ if (forbid_dac > 0 && mask > 0xffffffffULL)
+ return 0;
+
return 1;
}

-
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