On Thu, Aug 01, 2019 at 05:23:06PM +0100, Will Deacon wrote: > > - if (!dev_is_dma_coherent(dev) || (attrs & DMA_ATTR_WRITE_COMBINE)) > > - return pgprot_writecombine(prot); > > - return prot; > > + return pgprot_writecombine(prot); > > } > > Seems like a sensible cleanup to me: > > Acked-by: Will Deacon <w...@kernel.org> > > Although arch_dma_mmap_pgprot() is a bit of a misnomer now that it only > gets involved in the non-coherent case.
A better name is welcome. My other idea would be to just remove it entirely and do something like: #ifndef pgprot_dmacoherent #define pgprot_dmacoherent pgprot_noncached #endif pgprot_t dma_mmap_pgprot(struct device *dev, pgprot_t prot, unsigned long attrs) { if (dev_is_dma_coherent(dev) || (attrs & DMA_ATTR_NON_CONSISTENT)) return prot; #ifdef pgprot_writecombine if (attrs & DMA_ATTR_WRITE_COMBINE) return pgprot_writecombine(prot); #endif return pgprot_dmacoherent(prot); } But my worry is how this interacts with architectures that have an uncached segment (mips, nios2, microblaze, extensa) where we'd have the kernel access DMA_ATTR_WRITE_COMBINE mappigns using the uncached segment, and userspace mmaps using pgprot_writecombine, which could lead to aliasing issues. But then again mips already supports DMA_ATTR_WRITE_COMBINE, so this must be ok somehow. I guess I'll need to field that question to the relevant parties.