linux-kernel - Re: [RESEND PATCH v2 4/5] drm/msm: add DRM_MSM_GEM_SYNC

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Date:   Sun, 29 Nov 2020 10:51:08 -0800
From:   Rob Clark <robdclark@...il.com>
To:     Jonathan Marek <jonathan@...ek.ca>
Cc:     Christoph Hellwig <hch@....de>,
        Jordan Crouse <jcrouse@...eaurora.org>,
        freedreno <freedreno@...ts.freedesktop.org>,
        Sean Paul <sean@...rly.run>, David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        "open list:DRM DRIVER FOR MSM ADRENO GPU" 
        <linux-arm-msm@...r.kernel.org>,
        "open list:DRM DRIVER FOR MSM ADRENO GPU" 
        <dri-devel@...ts.freedesktop.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [RESEND PATCH v2 4/5] drm/msm: add DRM_MSM_GEM_SYNC_CACHE for
 non-coherent cache maintenance

On Mon, Nov 16, 2020 at 9:55 AM Jonathan Marek <jonathan@...ek.ca> wrote:
>
> On 11/16/20 12:50 PM, Rob Clark wrote:
> > On Mon, Nov 16, 2020 at 9:33 AM Christoph Hellwig <hch@....de> 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?

I was *assuming* (but could be wrong) that Jordan was referring to an
opencl cts test?

At any rate, it is sounding like you should add a
`MSM_PARAM_CACHE_ALIGNMENT` type of param that returns
dma_get_cache_alignment(), and then properly implement offset/end

BR,
-R