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Date:   Fri, 7 Dec 2018 02:38:41 +0100
From:   Christoph Hellwig <hch@lst.de>
To:     Christoph Hellwig <hch@lst.de>, "Clark, Rob" <robdclark@gmail.com>,
        Dave Airlie <airlied@linux.ie>,
        linux-arm-msm <linux-arm-msm@vger.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        dri-devel <dri-devel@lists.freedesktop.org>,
        Tomasz Figa <tfiga@chromium.org>,
        Sean Paul <seanpaul@chromium.org>, vivek.gautam@codeaurora.org,
        freedreno <freedreno@lists.freedesktop.org>,
        Robin Murphy <robin.murphy@arm.com>
Subject: Re: [PATCH v3 1/1] drm: msm: Replace dma_map_sg with dma_sync_sg*
Message-ID: <20181207013841.GA4530@lst.de>
References: <20181129140315.28476-1-vivek.gautam@codeaurora.org> <20181129141429.GA22638@lst.de> <CAF6AEGvsFbXGkC+=4oq1xXnoC2EVX2J0k-GqShefcek1=uw4Lw@mail.gmail.com> <CAKMK7uHOKtX2a12itSA0sDg=b77F+0vnLAdEvc_aNGRJTh85=Q@mail.gmail.com> <20181129155758.GC26537@lst.de> <20181129162807.GL21184@phenom.ffwll.local> <20181129165715.GA27786@lst.de> <CAKMK7uECLeTbEjG6=unWZSKakpiYkmBVbCEKKY2xv=vVjF-pBQ@mail.gmail.com> <20181129183334.GB30281@lst.de> <20181130094604.GV21184@phenom.ffwll.local>
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On Fri, Nov 30, 2018 at 10:46:04AM +0100, Daniel Vetter wrote:
> > Being able to dip into CMA and maybe iommu coalescing if we want to
> > get fancy is indeed the only reason for this API.  If we just wanted
> > to map pages we could already do that now with just a little bit
> > of boilerplate code (and quite a few drivers do - just adding this
> > new API will remove tons of code).
> 
> Sounds like the future is very bright indeed \o/

So, I spent some time with this and instead of a new API I think
it makes sure we have DMA_ATTR_NON_CONSISTENT consistently available
and with well defined semantics, that is virt_to_page on the return
value works, it is contiguos and we can use dma_sync_single_for_cpu
and dma_sync_single_for_device for ownership tranfers.

Can you graphics folks check if this:

    http://git.infradead.org/users/hch/misc.git/shortlog/refs/heads/dma-noncoherent-allocator

is something to work with?  Especially to get rid of the horrible
dma_get_sgtable hacks?