Hi Christoph,

Le mer. 30 sept. 2020 à 11:02, Christoph Hellwig hch@lst.de a écrit :

On Mon, Sep 28, 2020 at 03:31:28PM +0200, Paul Cercueil wrote:

...

It's allocated with dma_alloc_wc, but then it's only accessed as non-coherent.

Anyway, for the time being I guess you could revert 37054fc81443. But I have patches on top of it in drm-misc-next so it's going to be a mess.

If we have time I can come up with a custom dumb_create() fonction, to make sure that the GEM buffers are allocated with dma_alloc_noncoherent(). Is there a dma_mmap_noncoherent() too?

Please use the lower-level dma_alloc_pages and then just insert the pages directly using remap_pfn_range. Although it might make sense to eventually create a wrapper around remap_pfn_range for all the vma sizing sanity checks.

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.

-Paul