Le mer. 30 sept. 2020 à 18:40, Christoph Hellwig hch@lst.de a écrit :

On Wed, Sep 30, 2020 at 06:39:18PM +0200, Paul Cercueil wrote:

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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.

We don't have such a thing in the Linux API at all.

dma_pgprot(dev, vma->vm_page_prot, DMA_ATTR_NON_CONSISTENT);

That was giving me non-coherent cached memory, and now I don't have an alternative.

-Paul