On Monday 28 March 2016 14:29:29 Konrad Rzeszutek Wilk wrote: > > diff --git a/arch/arm64/mm/dma-mapping.c b/arch/arm64/mm/dma-mapping.c > > index ada00c3..8c0f66b 100644 > > --- a/arch/arm64/mm/dma-mapping.c > > +++ b/arch/arm64/mm/dma-mapping.c > > @@ -29,6 +29,14 @@ > > > > #include <asm/cacheflush.h> > > > > +/* > > + * If you are building a system without IOMMU, then you are using SWIOTLB > > + * library. The ARM64 adaptation of this library does not support address > > + * translation and it assumes that physical address = dma address for such > > + * a use case. Please don't build a platform that violates this. > > + */ > > Why not just expand the ARM64 part to support address translation? Because so far all hardware we have is relatively sane. We only need to implement this if someone accidentally puts their DMA space at the wrong address. There is at least one platform that could in theory use this because their RAM starts at an address that is outside of the reach of 32-bit devices, and a static IOMMU mapping (created by firmware) could be used to map the start of RAM into DMA address zero, to avoid having to use an IOMMU all the time, but it was considered not worth the effort to implement that. Arnd -- To unsubscribe from this list: send the line "unsubscribe linux-pci" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
