linux-kernel - Re: [RFC][PATCH 1/4] devicetree: bindings: Add linux,cma-heap tag for reserved memory

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Date:   Fri, 1 May 2020 11:42:16 +0100
From:   Brian Starkey <brian.starkey@....com>
To:     John Stultz <john.stultz@...aro.org>
Cc:     lkml <linux-kernel@...r.kernel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Sumit Semwal <sumit.semwal@...aro.org>,
        "Andrew F. Davis" <afd@...com>,
        Benjamin Gaignard <benjamin.gaignard@...aro.org>,
        Liam Mark <lmark@...eaurora.org>,
        Pratik Patel <pratikp@...eaurora.org>,
        Laura Abbott <labbott@...hat.com>,
        Chenbo Feng <fengc@...gle.com>,
        Alistair Strachan <astrachan@...gle.com>,
        Sandeep Patil <sspatil@...gle.com>,
        Hridya Valsaraju <hridya@...gle.com>,
        Christoph Hellwig <hch@....de>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        Robin Murphy <robin.murphy@....com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        devicetree@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        linux-mm@...ck.org, nd@....com
Subject: Re: [RFC][PATCH 1/4] devicetree: bindings: Add linux,cma-heap tag
 for reserved memory

Hi,

On Fri, May 01, 2020 at 07:39:46AM +0000, John Stultz wrote:
> This patch adds a linux,cma-heap property for CMA reserved memory
> regions, which will be used to allow the region to be exposed via
> the DMA-BUF Heaps interface
> 
> Cc: Rob Herring <robh+dt@...nel.org>
> Cc: Sumit Semwal <sumit.semwal@...aro.org>
> Cc: "Andrew F. Davis" <afd@...com>
> Cc: Benjamin Gaignard <benjamin.gaignard@...aro.org>
> Cc: Liam Mark <lmark@...eaurora.org>
> Cc: Pratik Patel <pratikp@...eaurora.org>
> Cc: Laura Abbott <labbott@...hat.com>
> Cc: Brian Starkey <Brian.Starkey@....com>
> Cc: Chenbo Feng <fengc@...gle.com>
> Cc: Alistair Strachan <astrachan@...gle.com>
> Cc: Sandeep Patil <sspatil@...gle.com>
> Cc: Hridya Valsaraju <hridya@...gle.com>
> Cc: Christoph Hellwig <hch@....de>
> Cc: Marek Szyprowski <m.szyprowski@...sung.com>
> Cc: Robin Murphy <robin.murphy@....com>
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> Cc: devicetree@...r.kernel.org
> Cc: dri-devel@...ts.freedesktop.org
> Cc: linux-mm@...ck.org
> Signed-off-by: John Stultz <john.stultz@...aro.org>
> ---
>  .../devicetree/bindings/reserved-memory/reserved-memory.txt    | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/Documentation/devicetree/bindings/reserved-memory/reserved-memory.txt b/Documentation/devicetree/bindings/reserved-memory/reserved-memory.txt
> index bac4afa3b197..e97b6a4c3bc0 100644
> --- a/Documentation/devicetree/bindings/reserved-memory/reserved-memory.txt
> +++ b/Documentation/devicetree/bindings/reserved-memory/reserved-memory.txt
> @@ -68,6 +68,9 @@ Linux implementation note:
>  - If a "linux,cma-default" property is present, then Linux will use the
>    region for the default pool of the contiguous memory allocator.
>  
> +- If a "linux,cma-heap" property is present, then Linux will expose the
> +  the CMA region via the DMA-BUF Heaps interface.
> +

Would it be useful or even possible to give some indication of what
the heap will end up being called? I'm afraid I don't remember what if
any conclusions came out of previous discussions on UAPI for heap
enumeration.

I suppose CMA names haven't been relevant to userspace before, but
they perhaps would be with this change.

Alternatively, leaving it effectively undefined doesn't tie us down,
and something like links in sysfs can be added as a richer API in the
future.

Cheers,
-Brian

>  - If a "linux,dma-default" property is present, then Linux will use the
>    region for the default pool of the consistent DMA allocator.
>  
> -- 
> 2.17.1
>