linux-kernel - Re: [PATCH v3 1/1] drm: msm: Replace dma_map_sg with dma_sync

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Message-ID: <20181207013841.GA4530@lst.de>
Date:   Fri, 7 Dec 2018 02:38:41 +0100
From:   Christoph Hellwig <hch@....de>
To:     Christoph Hellwig <hch@....de>, "Clark, Rob" <robdclark@...il.com>,
        Dave Airlie <airlied@...ux.ie>,
        linux-arm-msm <linux-arm-msm@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        Tomasz Figa <tfiga@...omium.org>,
        Sean Paul <seanpaul@...omium.org>, vivek.gautam@...eaurora.org,
        freedreno <freedreno@...ts.freedesktop.org>,
        Robin Murphy <robin.murphy@....com>
Subject: Re: [PATCH v3 1/1] drm: msm: Replace dma_map_sg with dma_sync_sg*

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?