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Subjectgeneric DMA bypass flag v4
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Hi all,

I've recently beeing chatting with Lu about using dma-iommu and
per-device DMA ops in the intel IOMMU driver, and one missing feature
in dma-iommu is a bypass mode where the direct mapping is used even
when an iommu is attached to improve performance. The powerpc
code already has a similar mode, so I'd like to move it to the core
DMA mapping code. As part of that I noticed that the current
powerpc code has a little bug in that it used the wrong check in the
dma_sync_* routines to see if the direct mapping code is used.

These two patches just add the generic code and move powerpc over,
the intel IOMMU bits will require a separate discussion.

The x86 AMD Gart code also has a bypass mode, but it is a lot
strange, so I'm not going to touch it for now.

Note that as-is this breaks the XSK buffer pool, which unfortunately
poked directly into DMA internals. A fix for that is already queued
up in the netdev tree.

Jesper and XDP gang: this should not regress any performance as
the dma-direct calls are now inlined into the out of line DMA mapping
calls. But if you can verify the performance numbers that would be
greatly appreciated.

A git tree is available here:

git://git.infradead.org/users/hch/misc.git dma-bypass.4

Gitweb:

git.infradead.org/users/hch/misc.git/shortlog/refs/heads/dma-bypass.4


Changes since v3:
- add config options for the dma ops bypass and dma ops themselves
to not increase the size of tinyconfig builds

Changes since v2:
- move the dma mapping helpers out of line
- check for possible direct mappings using the dma mask

Changes since v1:
- rebased to the current dma-mapping-for-next tree


Diffstat:
arch/alpha/Kconfig | 1
arch/arm/Kconfig | 1
arch/ia64/Kconfig | 1
arch/mips/Kconfig | 1
arch/parisc/Kconfig | 1
arch/powerpc/Kconfig | 2
arch/powerpc/include/asm/device.h | 5
arch/powerpc/kernel/dma-iommu.c | 90 +------------
arch/s390/Kconfig | 1
arch/sparc/Kconfig | 1
arch/x86/Kconfig | 1
drivers/iommu/Kconfig | 2
drivers/misc/mic/Kconfig | 1
drivers/vdpa/Kconfig | 1
drivers/xen/Kconfig | 1
include/linux/device.h | 11 +
include/linux/dma-direct.h | 104 +++++++++++++++
include/linux/dma-mapping.h | 251 ++++----------------------------------
kernel/dma/Kconfig | 12 +
kernel/dma/Makefile | 3
kernel/dma/direct.c | 74 -----------
kernel/dma/mapping.c | 214 ++++++++++++++++++++++++++++++--
22 files changed, 385 insertions(+), 394 deletions(-)

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