Le mer. 30 sept. 2020 à 18:11, Christoph Hellwig <hch@xxxxxx> 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
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