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 05:48:20 -0700
From:   Christoph Hellwig <hch@...radead.org>
To:     Laura Abbott <labbott@...hat.com>
Cc:     Christoph Hellwig <hch@...radead.org>,
        John Stultz <john.stultz@...aro.org>,
        lkml <linux-kernel@...r.kernel.org>,
        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>,
        "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 Wed, Jul 24, 2019 at 07:38:07AM -0400, Laura Abbott wrote:
> It's not just an optimization for Ion though. Ion was designed to
> let the callers choose between system and multiple CMA heaps.

Who cares about ion?  That some out of tree android crap that should
not be relevant for upstream except as an example for how not to design
things..

> On other
> systems there may be multiple CMA regions dedicated to a specific
> purpose or placed at a specific address. The callers need to
> be able to choose exactly whether they want a particular CMA region
> or discontiguous regions.

At least in cma is only used either with the global pool or a per-device
cma pool.  I think if you want to make this new dma-buf API fit in with
the rest with the kernel you follow that model, and pass in a struct
device to select the particular cma area, similar how the DMA allocator
works.