On Mon, Mar 19, 2018 at 06:01:41PM +0000, Catalin Marinas wrote: > I don't particularly like maintaining an arm64-specific dma-direct.h > either but arm64 seems to be the only architecture that needs to > potentially force a bounce when cache_line_size() > ARCH_DMA_MINALIGN > and the device is non-coherent.
mips is another likely candidate, see all the recent drama about dma_get_alignmet(). And I'm also having major discussion about even exposing the cache line size architecturally for RISC-V, so changes are high it'll have to deal with this mess sooner or later as they probably can't agree on a specific cache line size. > Note that lib/swiotlb.c doesn't even > deal with non-coherent DMA (e.g. map_sg doesn't have arch callbacks for > cache maintenance), so not disrupting lib/swiotlb.c seems to be the > least intrusive option. No yet. I have patches to consolidate the various swiotlb ops that deal with cache flushing or barriers. I was hoping to get them in for this merge window, but it probably is too late now given that I have a few other fires to fight. But they are going to be out early for the next merge window. > > Nevermind that the commit should at least be three different patches: > > > > (1) revert the broken original commit > > (2) increase the dma min alignment > > Reverting the original commit could, on its own, break an SoC which > expects ARCH_DMA_MINALIGN == 128. So these two should be a single commit > (my patch only reverts the L1_CACHE_BYTES change rather than > ARCH_DMA_MINALIGN, the latter being correct as 128). It would revert to the state before this commit. > As I said above, adding a check in swiotlb.c for > !is_device_dma_coherent(dev) && (ARCH_DMA_MINALIGN < cache_line_size()) > feels too architecture specific. And what exactly is architecture specific about that? It is a totally generic concept, which at this point also seems entirely theoretical based on the previous mail in this thread. _______________________________________________ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu
