Re: [RESEND PATCH v2 4/5] drm/msm: add DRM_MSM_GEM_SYNC_CACHE for non-coherent cache maintenance

[Jonathan Marek]

On 11/16/20 12:50 PM, Rob Clark wrote:
> On Mon, Nov 16, 2020 at 9:33 AM Christoph Hellwig <hch@xxxxxx> wrote:
> > On Sat, Nov 14, 2020 at 03:07:20PM -0500, Jonathan Marek wrote:
> > > qcom's vulkan driver has nonCoherentAtomSize=1, and it looks like
> > > dma_sync_single_for_cpu() does deal in some way with the partial cache line
> > > case, although I'm not sure that means we can have a nonCoherentAtomSize=1.
> >
> > No, it doesn't.  You need to ensure ownership is managed at
> > dma_get_cache_alignment() granularity.
>
> my guess is nonCoherentAtomSize=1 only works in the case of cache
> coherent buffers

nonCoherentAtomSize doesn't apply to coherent memory (as the name 
implies), I guess qcom's driver is just wrong about having 
nonCoherentAtomSize=1.

Jordan just mentioned there is at least one conformance test for this, I 
wonder if it just doesn't test it well enough, or just doesn't test the 
non-coherent memory type?