[RFC][PATCH 1/4] devicetree: bindings: Add linux,cma-heap tag for reserved memory
brian.starkey at arm.com
Mon May 4 08:50:07 UTC 2020
On Fri, May 01, 2020 at 11:40:16AM -0700, John Stultz wrote:
> On Fri, May 1, 2020 at 3:42 AM Brian Starkey <brian.starkey at arm.com> wrote:
> > 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 at kernel.org>
> > > Cc: Sumit Semwal <sumit.semwal at linaro.org>
> > > Cc: "Andrew F. Davis" <afd at ti.com>
> > > Cc: Benjamin Gaignard <benjamin.gaignard at linaro.org>
> > > Cc: Liam Mark <lmark at codeaurora.org>
> > > Cc: Pratik Patel <pratikp at codeaurora.org>
> > > Cc: Laura Abbott <labbott at redhat.com>
> > > Cc: Brian Starkey <Brian.Starkey at arm.com>
> > > Cc: Chenbo Feng <fengc at google.com>
> > > Cc: Alistair Strachan <astrachan at google.com>
> > > Cc: Sandeep Patil <sspatil at google.com>
> > > Cc: Hridya Valsaraju <hridya at google.com>
> > > Cc: Christoph Hellwig <hch at lst.de>
> > > Cc: Marek Szyprowski <m.szyprowski at samsung.com>
> > > Cc: Robin Murphy <robin.murphy at arm.com>
> > > Cc: Andrew Morton <akpm at linux-foundation.org>
> > > Cc: devicetree at vger.kernel.org
> > > Cc: dri-devel at lists.freedesktop.org
> > > Cc: linux-mm at kvack.org
> > > Signed-off-by: John Stultz <john.stultz at linaro.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.
> So the name we expose is the CMA name itself. So with dt it will be
> the name of the reserved memory node that the flag property is added
Yeah I'm just wondering if that's "stable" so we can say "the heap
will use the node name", or if saying that would cause us a headache
in the future.
> > 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.
> Hrm. Mind expanding on what you're thinking here?
Super hand-wavy, something like:
/sys/devices/blah/display at 2f000000/cma_region is a symlink to
I think danvet had some thoughts in this vein.
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