xiaomi-sm8450/android_kernel_xiaomi_sm8450
1
0
Fork 0
Code Issues Pull Requests Actions Packages Projects Releases Wiki Activity

x86/pci-dma: remove the experimental forcesac boot option

Browse Source 
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>
This commit is contained in:
Christoph Hellwig
2018-04-27 09:13:24 +02:00
parent 84564d1c76
commit 06e9552f5f
5 changed files with 6 additions and 30 deletions
Download Patch File Download Diff File Expand all files Collapse all files

21
arch/x86/kernel/pci-dma.c
View File

@@ -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);