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Date:   Thu, 25 Jul 2019 07:05:48 -0700
From:   Christoph Hellwig <hch@infradead.org>
To:     "Andrew F. Davis" <afd@ti.com>
Cc:     Christoph Hellwig <hch@infradead.org>,
        Laura Abbott <labbott@redhat.com>,
        John Stultz <john.stultz@linaro.org>,
        lkml <linux-kernel@vger.kernel.org>,
        Benjamin Gaignard <benjamin.gaignard@linaro.org>,
        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>,
        Xu YiPing <xuyiping@hisilicon.com>,
        "Chenfeng (puck)" <puck.chen@hisilicon.com>,
        butao <butao@hisilicon.com>,
        "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: <20190725140548.GB25010@infradead.org>
References: <20190624194908.121273-1-john.stultz@linaro.org>
 <20190624194908.121273-5-john.stultz@linaro.org>
 <20190718100840.GB19666@infradead.org>
 <CALAqxLWLx_tHVjZqrSNWfQ_M2RGGqh4qth3hi9GGRdSPov-gcw@mail.gmail.com>
 <20190724065958.GC16225@infradead.org>
 <25353c4f-5389-0352-b34e-78698b35e588@redhat.com>
 <20190725124820.GC20286@infradead.org>
 <18975c1a-7e4e-fab3-eec8-387fbf9dcfe5@ti.com>
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On Thu, Jul 25, 2019 at 09:47:11AM -0400, Andrew F. Davis wrote:
> This is a central allocator, it is not tied to any one device. If we
> knew the one device ahead of time we would just use the existing dma_alloc.
> 
> We might be able to solve some of that with late mapping after all the
> devices attach to the buffer, but even then, which device's CMA area
> would we chose to use from all the attached devices?
> 
> I can agree that allocating from per-device CMA using Heaps doesn't make
> much sense, but for global pools I'm not sure I see any way to allow
> devices to select which pool is right for a specific use. They don't
> have the full use-case information like the application does, the
> selection needs to be made from the application.

Well, the examples we had before was that we clear want to use the
per-device CMA area.  And at least in upstream a CMA area either is
global or attached to a device, as we otherwise wouldn't find it.