This patchset adds per-device dma_mapping_ops support for
CONFIG_X86_64 like POWER architecture does. This change enables us to
cleanly fix the Calgary IOMMU issue that some devices are not behind
the IOMMU [1]. It also would be helpful to handle KVM PCI passthrough.

A pointer to dma_mapping_ops to struct dev_archdata is added. If the
pointer is non NULL, DMA operations in asm/dma-mapping.h use it. If
it's NULL, the system-wide dma_ops pointer is used as before.

The major obstacle is that dma_mapping_error doesn't take a pointer to
the device unlike other DMA operations. So x86 can't have
dma_mapping_ops per device. Note all the POWER IOMMUs use the same
dma_mapping_error function so this is not a problem for POWER but x86
IOMMUs use different dma_mapping_error functions.

The first patch adds the device argument to dma_mapping_error. The
patch is trivial but large since it touches lots of drivers and
dma-mapping.h in all the architecture.

[1] http://lkml.org/lkml/2008/5/8/423


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原文链接: http://lkml.org/lkml/2008/5/13/36