linux-kernel - Re: [PATCH v2 4/4] dma-buf: heaps: add chunk heap to dmabuf heaps

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Message-ID: <20201201225554.GA3968963@google.com>
Date:   Tue, 1 Dec 2020 14:55:54 -0800
From:   Minchan Kim <minchan@...nel.org>
To:     John Stultz <john.stultz@...aro.org>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        LKML <linux-kernel@...r.kernel.org>,
        linux-mm <linux-mm@...ck.org>, Hyesoo Yu <hyesoo.yu@...sung.com>,
        Matthew Wilcox <willy@...radead.org>, david@...hat.com,
        iamjoonsoo.kim@....com, vbabka@...e.cz,
        Suren Baghdasaryan <surenb@...gle.com>,
        KyongHo Cho <pullip.cho@...sung.com>,
        John Dias <joaodias@...gle.com>,
        Hridya Valsaraju <hridya@...gle.com>,
        Sumit Semwal <sumit.semwal@...aro.org>,
        Brian Starkey <Brian.Starkey@....com>,
        linux-media <linux-media@...r.kernel.org>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>, Rob Herring <robh@...nel.org>,
        Christian Koenig <christian.koenig@....com>,
        "moderated list:DMA BUFFER SHARING FRAMEWORK" 
        <linaro-mm-sig@...ts.linaro.org>
Subject: Re: [PATCH v2 4/4] dma-buf: heaps: add chunk heap to dmabuf heaps

On Tue, Dec 01, 2020 at 11:48:15AM -0800, John Stultz wrote:
> On Tue, Dec 1, 2020 at 9:51 AM Minchan Kim <minchan@...nel.org> wrote:
> 
> Thanks for reworking and resending this!
> 
> ...
> > +static int __init chunk_heap_init(void)
> > +{
> > +       struct cma *default_cma = dev_get_cma_area(NULL);
> > +       struct dma_heap_export_info exp_info;
> > +       struct chunk_heap *chunk_heap;
> > +
> > +       if (!default_cma)
> > +               return 0;
> > +
> > +       chunk_heap = kzalloc(sizeof(*chunk_heap), GFP_KERNEL);
> > +       if (!chunk_heap)
> > +               return -ENOMEM;
> > +
> > +       chunk_heap->order = CHUNK_HEAP_ORDER;
> > +       chunk_heap->cma = default_cma;
> > +
> > +       exp_info.name = cma_get_name(default_cma);
> 
> So, this would create a chunk heap name with the default CMA name,
> which would be indistinguishable from the heap name used for the plain
> CMA heap.
> 
> Probably a good idea to prefix it with "chunk-" so the heap device
> names are unique?

That will give an impression to user that they are using different CMA
area but that's not true. IMHO, let's be honest at this moment.
When DT binding with CMA is landing down, it could provide unique name.
Thought?