From: Alexey Kardashevskiy aik@ozlabs.ru
[ Upstream commit 23c216b335d1fbd716076e8263b54a714ea3cf0e ]
According to dma-api.rst, the dma_get_required_mask() helper should return "the mask that the platform requires to operate efficiently". Which in the case of PPC64 means the bypass mask and not a mask from an IOMMU table which is shorter and slower to use due to map/unmap operations (especially expensive on "pseries").
However the existing implementation ignores the possibility of bypassing and returns the IOMMU table mask on the pseries platform which makes some drivers (mpt3sas is one example) choose 32bit DMA even though bypass is supported. The powernv platform sort of handles it by having a bigger default window with a mask >=40 but it only works as drivers choose 63/64bit if the required mask is >32 which is rather pointless.
This reintroduces the bypass capability check to let drivers make a better choice of the DMA mask.
Fixes: f1565c24b596 ("powerpc: use the generic dma_ops_bypass mode") Signed-off-by: Alexey Kardashevskiy aik@ozlabs.ru Reviewed-by: Christoph Hellwig hch@lst.de Signed-off-by: Michael Ellerman mpe@ellerman.id.au Link: https://lore.kernel.org/r/20210930034454.95794-1-aik@ozlabs.ru Signed-off-by: Sasha Levin sashal@kernel.org --- arch/powerpc/kernel/dma-iommu.c | 9 +++++++++ 1 file changed, 9 insertions(+)
diff --git a/arch/powerpc/kernel/dma-iommu.c b/arch/powerpc/kernel/dma-iommu.c index a1c744194018..9ac0651795cf 100644 --- a/arch/powerpc/kernel/dma-iommu.c +++ b/arch/powerpc/kernel/dma-iommu.c @@ -117,6 +117,15 @@ u64 dma_iommu_get_required_mask(struct device *dev) struct iommu_table *tbl = get_iommu_table_base(dev); u64 mask;
+ if (dev_is_pci(dev)) { + u64 bypass_mask = dma_direct_get_required_mask(dev); + + if (dma_iommu_dma_supported(dev, bypass_mask)) { + dev_info(dev, "%s: returning bypass mask 0x%llx\n", __func__, bypass_mask); + return bypass_mask; + } + } + if (!tbl) return 0;