Revert "iommu/dma: Add config for PCI SAC address trick"

[linux-2.6-microblaze.git] / drivers / iommu / Kconfig

diff --git a/drivers/iommu/Kconfig b/drivers/iommu/Kconfig
index 50bc696..5c5cb5b 100644 (file)
--- a/drivers/iommu/Kconfig
+++ b/drivers/iommu/Kconfig
@@ -144,32 +144,6 @@ config IOMMU_DMA
        select IRQ_MSI_IOMMU
        select NEED_SG_DMA_LENGTH
 
-config IOMMU_DMA_PCI_SAC
-       bool "Enable 64-bit legacy PCI optimisation by default"
-       depends on IOMMU_DMA
-       help
-         Enable by default an IOMMU optimisation for 64-bit legacy PCI devices,
-         wherein the DMA API layer will always first try to allocate a 32-bit
-         DMA address suitable for a single address cycle, before falling back
-         to allocating from the device's full usable address range. If your
-         system has 64-bit legacy PCI devices in 32-bit slots where using dual
-         address cycles reduces DMA throughput significantly, this may be
-         beneficial to overall performance.
-
-         If you have a modern PCI Express based system, this feature mostly just
-         represents extra overhead in the allocation path for no practical
-         benefit, and it should usually be preferable to say "n" here.
-
-         However, beware that this feature has also historically papered over
-         bugs where the IOMMU address width and/or device DMA mask is not set
-         correctly. If device DMA problems and IOMMU faults start occurring
-         after disabling this option, it is almost certainly indicative of a
-         latent driver or firmware/BIOS bug, which would previously have only
-         manifested with several gigabytes worth of concurrent DMA mappings.
-
-         If this option is not set, the feature can still be re-enabled at
-         boot time with the "iommu.forcedac=0" command-line argument.
-
 # Shared Virtual Addressing
 config IOMMU_SVA
        bool