linux-kernel - Re: [PATCH v6 4/5] dma-buf: heaps: Add CMA heap to dmabuf heaps

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Date:   Thu, 25 Jul 2019 07:33:35 -0700
From:   Christoph Hellwig <hch@...radead.org>
To:     Benjamin Gaignard <benjamin.gaignard@...aro.org>
Cc:     Christoph Hellwig <hch@...radead.org>,
        John Stultz <john.stultz@...aro.org>,
        lkml <linux-kernel@...r.kernel.org>,
        Laura Abbott <labbott@...hat.com>,
        Sumit Semwal <sumit.semwal@...aro.org>,
        Liam Mark <lmark@...eaurora.org>,
        Pratik Patel <pratikp@...eaurora.org>,
        Brian Starkey <Brian.Starkey@....com>,
        Vincent Donnefort <Vincent.Donnefort@....com>,
        Sudipto Paul <Sudipto.Paul@....com>,
        "Andrew F . Davis" <afd@...com>,
        Xu YiPing <xuyiping@...ilicon.com>,
        "Chenfeng (puck)" <puck.chen@...ilicon.com>,
        butao <butao@...ilicon.com>,
        "Xiaqing (A)" <saberlily.xia@...ilicon.com>,
        Yudongbin <yudongbin@...ilicon.com>,
        Chenbo Feng <fengc@...gle.com>,
        Alistair Strachan <astrachan@...gle.com>,
        dri-devel <dri-devel@...ts.freedesktop.org>
Subject: Re: [PATCH v6 4/5] dma-buf: heaps: Add CMA heap to dmabuf heaps

On Thu, Jul 25, 2019 at 03:20:11PM +0200, Benjamin Gaignard wrote:
> > But that just means we need a flag that memory needs to be contiguous,
> > which totally makes sense at the API level.  But CMA is not the only
> > source of contigous memory, so we should not conflate the two.
> 
> We have one file descriptor per heap to be able to add access control
> on each heap.
> That wasn't possible with ION because the heap was selected given the
> flags in ioctl
> structure and we can't do access control based on that. If we put flag
> to select the
> allocation mechanism (system, CMA, other) in ioctl we come back to ION status.
> For me one allocation mechanism = one heap.

Well, I agree with your split for different fundamentally different
allocators.  But the point is that CMA (at least the system cma area)
fundamentally isn't a different allocator.  The per-device CMA area
still are kinda the same, but you can just have one fd for each
per-device CMA area to make your life simple.