From 388c19e176436707eb30a81c7e4129e08769f92b Mon Sep 17 00:00:00 2001
From: Andi Kleen <ak@suse.de>
Date: Wed, 20 Jun 2007 12:23:32 +0200
Subject: [PATCH] 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>
---
 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(+)

diff --git a/arch/i386/kernel/pci-dma.c b/arch/i386/kernel/pci-dma.c
index 30b754f7cb..048f09b625 100644
--- a/arch/i386/kernel/pci-dma.c
+++ b/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(struct device *dev,
 	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
diff --git a/arch/x86_64/kernel/pci-dma.c b/arch/x86_64/kernel/pci-dma.c
index 651ccfb066..9f80aad3fe 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);
diff --git a/include/asm-i386/dma-mapping.h b/include/asm-i386/dma-mapping.h
index 183eebeebb..f1d72d177f 100644
--- a/include/asm-i386/dma-mapping.h
+++ b/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 mask)
         if(mask < 0x00ffffff)
                 return 0;
 
+	/* Work around chipset bugs */
+	if (forbid_dac > 0 && mask > 0xffffffffULL)
+		return 0;
+
 	return 1;
 }
 
-- 
2.11.4.GIT