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

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Message-ID: <CAF6AEGuFzsurd4n6G-nUmCusTJ8vMo9Kqjzs3JRS_d6n+qHgEA@mail.gmail.com>
Date:   Mon, 16 Nov 2020 09:50:28 -0800
From:   Rob Clark <robdclark@...il.com>
To:     Christoph Hellwig <hch@....de>
Cc:     Jonathan Marek <jonathan@...ek.ca>,
        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 9:33 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

BR,
-R