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dma-direct: always allow dma mask <= physiscal memory size

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This way an architecture with less than 4G of RAM can support dma_mask
smaller than 32-bit without a ZONE_DMA.  Apparently that is a common
case on powerpc.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Robin Murphy <robin.murphy@arm.com>
This commit is contained in:
Christoph Hellwig 2018-09-07 09:31:58 +02:00
parent b4ebe60632
commit 9d7a224b46
1 changed files with 16 additions and 12 deletions
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28
kernel/dma/direct.c
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@ -284,21 +284,25 @@ int dma_direct_map_sg(struct device *dev, struct scatterlist *sgl, int nents,
return nents;
}
/*
* Because 32-bit DMA masks are so common we expect every architecture to be
* able to satisfy them - either by not supporting more physical memory, or by
* providing a ZONE_DMA32. If neither is the case, the architecture needs to
* use an IOMMU instead of the direct mapping.
*/
int dma_direct_supported(struct device *dev, u64 mask)
{
#ifdef CONFIG_ZONE_DMA
if (mask < phys_to_dma(dev, DMA_BIT_MASK(ARCH_ZONE_DMA_BITS)))
u64 min_mask;
if (IS_ENABLED(CONFIG_ZONE_DMA))
min_mask = DMA_BIT_MASK(ARCH_ZONE_DMA_BITS);
else
min_mask = DMA_BIT_MASK(32);
min_mask = min_t(u64, min_mask, (max_pfn - 1) << PAGE_SHIFT);
if (mask >= phys_to_dma(dev, min_mask))
return 0;
#else
/*
* Because 32-bit DMA masks are so common we expect every architecture
* to be able to satisfy them - either by not supporting more physical
* memory, or by providing a ZONE_DMA32. If neither is the case, the
* architecture needs to use an IOMMU instead of the direct mapping.
*/
if (mask < phys_to_dma(dev, DMA_BIT_MASK(32)))
return 0;
#endif
return 1;
}