From ece668401250c1d0419ed078c1d26ccdd30d3289 Mon Sep 17 00:00:00 2001
From: Andi Kleen <ak@suse.de>
Date: Sat, 30 Sep 2006 01:47:55 +0200
Subject: [PATCH] Allow disabling DAC using command line options
Might or might not work around some reported bugs on VIA systems.
Signed-off-by: Andi Kleen <ak@suse.de>
---
Documentation/x86_64/boot-options.txt | 4 ++++
arch/x86_64/kernel/pci-dma.c | 18 ++++++++++++++++++
2 files changed, 22 insertions(+)
diff --git a/Documentation/x86_64/boot-options.txt b/Documentation/x86_64/boot-options.txt
index 4303e0c124..e97a4c8fe6 100644
--- a/Documentation/x86_64/boot-options.txt
+++ b/Documentation/x86_64/boot-options.txt
@@ -199,6 +199,10 @@ IOMMU
allowed overwrite iommu off workarounds for specific chipsets.
soft Use software bounce buffering (default for Intel machines)
noaperture Don't touch the aperture for AGP.
+ allowdac Allow DMA >4GB
+ When off all DMA over >4GB is forced through an IOMMU or bounce
+ buffering.
+ nodac Forbid DMA >4GB
swiotlb=pages[,force]
diff --git a/arch/x86_64/kernel/pci-dma.c b/arch/x86_64/kernel/pci-dma.c
index 4dcb671bd1..225e19941b 100644
--- a/arch/x86_64/kernel/pci-dma.c
+++ b/arch/x86_64/kernel/pci-dma.c
@@ -170,8 +170,20 @@ void dma_free_coherent(struct device *dev, size_t size,
}
EXPORT_SYMBOL(dma_free_coherent);
+static int forbid_dac __read_mostly;
+
int dma_supported(struct device *dev, u64 mask)
{
+#ifdef CONFIG_PCI
+ if (mask > 0xffffffff && forbid_dac > 0) {
+
+
+
+ printk(KERN_INFO "PCI: Disallowing DAC for device %s\n", dev->bus_id);
+ return 0;
+ }
+#endif
+
if (dma_ops->dma_supported)
return dma_ops->dma_supported(dev, mask);
@@ -231,6 +243,8 @@ EXPORT_SYMBOL(dma_set_mask);
allowed overwrite iommu off workarounds for specific chipsets.
soft Use software bounce buffering (default for Intel machines)
noaperture Don't touch the aperture for AGP.
+ allowdac Allow DMA >4GB
+ nodac Forbid DMA >4GB
*/
__init int iommu_setup(char *p)
{
@@ -267,6 +281,10 @@ __init int iommu_setup(char *p)
iommu_merge = 0;
if (!strncmp(p, "forcesac",8))
iommu_sac_force = 1;
+ if (!strncmp(p, "allowdac", 8))
+ forbid_dac = 0;
+ if (!strncmp(p, "nodac", 5))
+ forbid_dac = -1;
#ifdef CONFIG_SWIOTLB
if (!strncmp(p, "soft",4))
--
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