On Wed, Sep 30, 2020 at 03:33:13PM +0200, Paul Cercueil wrote: > One thing missing for remap_pfn_range(), I have no alternative for this: > > vma->vm_page_prot = dma_pgprot(dev, vma->vm_page_prot, > DMA_ATTR_NON_CONSISTENT); > > So I have to do: > > vma->vm_page_prot = pgprot_noncached(vma->vm_page_prot); > pgprot_val(vma->vm_page_prot) &= ~_CACHE_MASK; > pgprot_val(vma->vm_page_prot) |= _CACHE_CACHABLE_NONCOHERENT; > > And that will only compile on MIPS, because these _CACHE_* macros are only > defined there. > > I would need something like a pgprot_noncoherent(), I think. dma_alloc_pages gives you cached memory, so you can't just use an uncached protection for the userspace mmap here. If you want uncached memory you need to use dma_alloc_coherent paired with dma_mmap_coherent. Or dma_alloc_wc for a slightly different flavor of uncached. (both of the map to dma_alloc_attrs / dma_mmap_attrs eventually).
