[PATCH 0/4] DMA mapping changes for SCSI core

John Garry
2022-05-20T08:29:29Z

As reported in [0], DMA mappings whose size exceeds the IOMMU IOVA caching
limit may see a big performance hit.

This series introduces a new DMA mapping API, dma_opt_mapping_size(), so
that drivers may know this limit when performance is a factor in the
mapping.

Robin didn't like using dma_max_mapping_size() for this [1]. An
alternative to adding the new API would be to add a "hard_limit" arg
to dma_max_mapping_size(). This would mean fixing up all current users,
but it would be good to do that anyway as not all users require a hard
limit.

The SCSI core coded is modified to use this limit.

I also added a patch for libata-scsi as it does not currently honour the
shost max_sectors limit.

[0] https://lore.kernel.org/linux-iommu/20210129092120.1482-1-thunder.leizhen@huawei.com/
[1] https://lore.kernel.org/linux-iommu/f5b78c9c-312e-70ab-ecbb-f14623a4b6e3@arm.com/

John Garry (4):
dma-mapping: Add dma_opt_mapping_size()
dma-iommu: Add iommu_dma_opt_mapping_size()
scsi: core: Cap shost max_sectors according to DMA optimum mapping
limits
libata-scsi: Cap ata_device->max_sectors according to
shost->max_sectors

Documentation/core-api/dma-api.rst | 9 +++++++++
drivers/ata/libata-scsi.c | 1 +
drivers/iommu/dma-iommu.c | 6 ++++++
drivers/iommu/iova.c | 5 +++++
drivers/scsi/hosts.c | 5 +++++
drivers/scsi/scsi_lib.c | 4 ----
include/linux/dma-map-ops.h | 1 +
include/linux/dma-mapping.h | 5 +++++
include/linux/iova.h | 2 ++
kernel/dma/mapping.c | 12 ++++++++++++
10 files changed, 46 insertions(+), 4 deletions(-)

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2.26.2