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Date:   Thu, 25 Jul 2019 07:33:35 -0700
From:   Christoph Hellwig <hch@infradead.org>
To:     Benjamin Gaignard <benjamin.gaignard@linaro.org>
Cc:     Christoph Hellwig <hch@infradead.org>,
        John Stultz <john.stultz@linaro.org>,
        lkml <linux-kernel@vger.kernel.org>,
        Laura Abbott <labbott@redhat.com>,
        Sumit Semwal <sumit.semwal@linaro.org>,
        Liam Mark <lmark@codeaurora.org>,
        Pratik Patel <pratikp@codeaurora.org>,
        Brian Starkey <Brian.Starkey@arm.com>,
        Vincent Donnefort <Vincent.Donnefort@arm.com>,
        Sudipto Paul <Sudipto.Paul@arm.com>,
        "Andrew F . Davis" <afd@ti.com>,
        Xu YiPing <xuyiping@hisilicon.com>,
        "Chenfeng (puck)" <puck.chen@hisilicon.com>,
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        "Xiaqing (A)" <saberlily.xia@hisilicon.com>,
        Yudongbin <yudongbin@hisilicon.com>,
        Chenbo Feng <fengc@google.com>,
        Alistair Strachan <astrachan@google.com>,
        dri-devel <dri-devel@lists.freedesktop.org>
Subject: Re: [PATCH v6 4/5] dma-buf: heaps: Add CMA heap to dmabuf heaps
Message-ID: <20190725143335.GB21894@infradead.org>
References: <20190624194908.121273-1-john.stultz@linaro.org>
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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.