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Date:   Thu, 25 Jul 2019 07:04:48 -0700
From:   Christoph Hellwig <hch@infradead.org>
To:     "Andrew F. Davis" <afd@ti.com>
Cc:     Christoph Hellwig <hch@infradead.org>,
        John Stultz <john.stultz@linaro.org>,
        lkml <linux-kernel@vger.kernel.org>,
        Laura Abbott <labbott@redhat.com>,
        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: <20190725140448.GA25010@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>
 <8e6f8e4f-20fc-1f1f-2228-f4fd7c7c5c1f@ti.com>
 <20190725125014.GD20286@infradead.org>
 <0eae0024-1fdf-bd06-a8ff-1a41f0af3c69@ti.com>
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On Thu, Jul 25, 2019 at 09:31:50AM -0400, Andrew F. Davis wrote:
> But that's just it, dma-buf does not assume buffers are backed by normal
> kernel managed memory, it is up to the buffer exporter where and when to
> allocate the memory. The memory backed by this SRAM buffer does not have
> the normal struct page backing. So moving the map, sync, etc functions
> to common code would fail for this and many other heap types. This was a
> major problem with Ion that prompted this new design.

The code clearly shows it has page backing, e.g. this:

+	sg_set_page(table->sgl, pfn_to_page(PFN_DOWN(buffer->paddr)), buffer->len, 0);

and the fact that it (and the dma-buf API) uses scatterlists, which 
requires pages.