[PATCH 1/2] drm/shmem: Use cached mappings by default

Rob Herring robh at kernel.org
Thu May 14 20:36:45 UTC 2020

On Thu, May 14, 2020 at 7:40 AM Daniel Vetter <daniel at ffwll.ch> wrote:
> On Wed, May 13, 2020 at 05:03:11PM +0200, Thomas Zimmermann wrote:
> > SHMEM-buffer backing storage is allocated from system memory; which is
> > typically cachable. Currently, only virtio uses cachable mappings; udl
> > uses its own vmap/mmap implementation for cachable mappings. Other
> > drivers default to writecombine mappings.
> I'm pretty sure this breaks all these drivers. quick grep on a few
> functions says this is used by lima, panfrost, v3d. And they definitely
> need uncached/wc stuff afaiui. Or I'm completely missing something?

Yes, that would be my guess. DMA is usually non-coherent on Arm.


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