linux-kernel - Re: [PATCH 2/3] drm/msm: add DRM_MSM_GEM_SYNC_CACHE for non-coherent cache maintenance

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Date:   Fri, 23 Oct 2020 07:48:32 +0100
From:   Christoph Hellwig <hch@...radead.org>
To:     Christoph Hellwig <hch@...radead.org>,
        Robin Murphy <robin.murphy@....com>,
        Jonathan Marek <jonathan@...ek.ca>,
        David Airlie <airlied@...ux.ie>,
        freedreno@...ts.freedesktop.org,
        open list <linux-kernel@...r.kernel.org>,
        "open list:DRM DRIVER FOR MSM ADRENO GPU" 
        <dri-devel@...ts.freedesktop.org>,
        iommu@...ts.linux-foundation.org,
        "open list:DRM DRIVER FOR MSM ADRENO GPU" 
        <linux-arm-msm@...r.kernel.org>, Sean Paul <sean@...rly.run>
Subject: Re: [PATCH 2/3] drm/msm: add DRM_MSM_GEM_SYNC_CACHE for non-coherent
 cache maintenance

On Thu, Oct 15, 2020 at 04:43:01PM +0100, Christoph Hellwig wrote:
> > Somewhat related, but is there a way to tell the dma-api to fail instead
> > of falling back to swiotlb? In many case for gpu drivers it's much better
> > if we fall back to dma_alloc_coherent and manage the copying ourselves
> > instead of abstracting this away in the dma-api. Currently that's "solved"
> > rather pessimistically by always allocating from dma_alloc_coherent if
> > swiotlb could be in the picture (at least for ttm based drivers, i915 just
> > falls over).
> 
> Is this for the alloc_pages plus manually map logic in various drivers?
> 
> They should switch to the new dma_alloc_pages API that I'll send to
> Linus for 5.10 soon.

Daniel, can you clarify this?