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authorChristoph Hellwig <hch@lst.de>2018-04-27 09:13:24 +0200
committerChristoph Hellwig <hch@lst.de>2018-05-28 12:48:16 +0200
commit06e9552f5f12564dc1c3483f0934d96cc4f72f18 (patch)
tree48c92eba3b3c1a7e8576fc84159183481e5e2960 /arch/x86/kernel
parent84564d1c76255ac6d5fb76c85818cb5961fad061 (diff)
x86/pci-dma: remove the experimental forcesac boot option
Limiting the dma mask to avoid PCI (pre-PCIe) DAC cycles while paying the huge overhead of an IOMMU is rather pointless, and this seriously gets in the way of dma mapping work. Signed-off-by: Christoph Hellwig <hch@lst.de> Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Diffstat (limited to 'arch/x86/kernel')
-rw-r--r--arch/x86/kernel/pci-dma.c21
1 files changed, 1 insertions, 20 deletions
diff --git a/arch/x86/kernel/pci-dma.c b/arch/x86/kernel/pci-dma.c
index c7113fd18e32..b65b0d7072f1 100644
--- a/arch/x86/kernel/pci-dma.c
+++ b/arch/x86/kernel/pci-dma.c
@@ -20,8 +20,6 @@ static int forbid_dac __read_mostly;
const struct dma_map_ops *dma_ops = &dma_direct_ops;
EXPORT_SYMBOL(dma_ops);
-static int iommu_sac_force __read_mostly;
-
#ifdef CONFIG_IOMMU_DEBUG
int panic_on_overflow __read_mostly = 1;
int force_iommu __read_mostly = 1;
@@ -122,7 +120,7 @@ static __init int iommu_setup(char *p)
if (!strncmp(p, "nomerge", 7))
iommu_merge = 0;
if (!strncmp(p, "forcesac", 8))
- iommu_sac_force = 1;
+ pr_warn("forcesac option ignored.\n");
if (!strncmp(p, "allowdac", 8))
forbid_dac = 0;
if (!strncmp(p, "nodac", 5))
@@ -162,23 +160,6 @@ int arch_dma_supported(struct device *dev, u64 mask)
}
#endif
- /* Tell the device to use SAC when IOMMU force is on. This
- allows the driver to use cheaper accesses in some cases.
-
- Problem with this is that if we overflow the IOMMU area and
- return DAC as fallback address the device may not handle it
- correctly.
-
- As a special case some controllers have a 39bit address
- mode that is as efficient as 32bit (aic79xx). Don't force
- SAC for these. Assume all masks <= 40 bits are of this
- type. Normally this doesn't make any difference, but gives
- more gentle handling of IOMMU overflow. */
- if (iommu_sac_force && (mask >= DMA_BIT_MASK(40))) {
- dev_info(dev, "Force SAC with mask %Lx\n", mask);
- return 0;
- }
-
return 1;
}
EXPORT_SYMBOL(arch_dma_supported);