tree c582777858d9da5c8d70cad910a04859b213fd8f
parent 942a8186eb4451700dadd1d60a2e43ce67605991
author John Garry <john.garry@huawei.com> 1657797324 +0800
committer Christoph Hellwig <hch@lst.de> 1658203541 +0200

dma-mapping: add dma_opt_mapping_size()

Streaming DMA mapping involving an IOMMU may be much slower for larger
total mapping size. This is because every IOMMU DMA mapping requires an
IOVA to be allocated and freed. IOVA sizes above a certain limit are not
cached, which can have a big impact on DMA mapping performance.

Provide an API for device drivers to know this "optimal" limit, such that
they may try to produce mapping which don't exceed it.

Signed-off-by: John Garry <john.garry@huawei.com>
Reviewed-by: Damien Le Moal <damien.lemoal@opensource.wdc.com>
Acked-by: Martin K. Petersen <martin.petersen@oracle.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>