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

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Message-ID: <b2170efd-df80-b54b-9ffe-8183befe5e00@ti.com>
Date:   Thu, 25 Jul 2019 10:25:50 -0400
From:   "Andrew F. Davis" <afd@...com>
To:     Christoph Hellwig <hch@...radead.org>
CC:     John Stultz <john.stultz@...aro.org>,
        lkml <linux-kernel@...r.kernel.org>,
        Laura Abbott <labbott@...hat.com>,
        Benjamin Gaignard <benjamin.gaignard@...aro.org>,
        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>,
        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 7/25/19 10:11 AM, Christoph Hellwig wrote:
> On Thu, Jul 25, 2019 at 10:10:08AM -0400, Andrew F. Davis wrote:
>> Pages yes, but not "normal" pages from the kernel managed area.
>> page_to_pfn() will return bad values on the pages returned by this
>> allocator and so will any of the kernel sync/map functions. Therefor
>> those operations cannot be common and need special per-heap handling.
> 
> Well, that means this thing is buggy and abuses the scatterlist API
> and we can't merge it anyway, so it is irrelevant.
> 

Since when do scatterlists need to only have kernel virtual backed
memory pages? Device memory is stored in scatterlists and
dma_sync_sg_for_* would fail just the same when the cache ops were
attempted.