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

[John Garry]

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@xxxxxxxxxx/
[1] https://lore.kernel.org/linux-iommu/f5b78c9c-312e-70ab-ecbb-f14623a4b6e3@xxxxxxx/

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(-)

-- 
2.26.2