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SubjectRe: linux-next: build failure after merge of the drm tree


Le lun. 28 sept. 2020 à 14:10, Christoph Hellwig <hch@lst.de> a écrit
:
> On Mon, Sep 28, 2020 at 01:46:55PM +0200, Paul Cercueil wrote:
>>> dma_mmap_attrs can only be used on allocations from dma_mmap_attrs
>>> with
>>> the same attrs. As there is no allocation using
>>> DMA_ATTR_NON_CONSISTENT
>>> in the drm core, something looks very fishy here.
>>
>> Is that a fact? I don't see why you couldn't change the cache
>> settings
>> after allocation. In practice it works just fine.
>
> Accessing the same physical address using different caching attributes
> is undefined behavior and fairly dangerous on most architectures, and
> thus not supported by the DMA API.

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?

-Paul


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