Le mer. 30 sept. 2020 à 18:11, Christoph Hellwig hch@lst.de a écrit :

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).

I don't want uncached memory, I want non-coherent cached memory.

-Paul