Re: [RFC][PATCH 1/3] dt-bindings: dma-buf: heaps: Describe CMA regions to be added to dmabuf heaps interface.

From: Rob Herring <robh@kernel.org>
To: John Stultz <john.stultz@linaro.org>
Cc: Rob Herring <rob.e.herring@gmail.com>,
	lkml <linux-kernel@vger.kernel.org>,
	Mark Rutland <mark.rutland@arm.com>,
	Laura Abbott <labbott@redhat.com>,
	Benjamin Gaignard <benjamin.gaignard@linaro.org>,
	Sumit Semwal <sumit.semwal@linaro.org>,
	Liam Mark <lmark@codeaurora.org>,
	Pratik Patel <pratikp@codeaurora.org>,
	Brian Starkey <Brian.Starkey@arm.com>,
	"Andrew F . Davis" <afd@ti.com>, Chenbo Feng <fengc@google.com>,
	Alistair Strachan <astrachan@google.com>,
	Sandeep Patil <sspatil@google.com>,
	Hridya Valsaraju <hridya@google.com>,
	devicetree <devicetree@vger.kernel.org>,
	dri-devel <dri-devel@lists.freedesktop.org>
Subject: Re: [RFC][PATCH 1/3] dt-bindings: dma-buf: heaps: Describe CMA regions to be added to dmabuf heaps interface.
Date: Wed, 30 Oct 2019 08:29:32 -0500	[thread overview]
Message-ID: <20191030132932.GA7292@bogus> (raw)
In-Reply-To: <CALAqxLXG8LrWAQevEyj7BJ00CiAkodfgFMdCbuMRucO5w5yhKg@mail.gmail.com>

On Fri, Oct 25, 2019 at 04:55:35PM -0700, John Stultz wrote:
> On Fri, Oct 25, 2019 at 4:32 PM Rob Herring <rob.e.herring@gmail.com> wrote:
> >
> > On Fri, Oct 25, 2019 at 5:51 PM John Stultz <john.stultz@linaro.org> wrote:
> > >
> > > This binding specifies which CMA regions should be added to the
> > > dmabuf heaps interface.
> >
> > Is this an ION DT binding in disguise? I thought I killed that. ;)
> 
> Maybe? I may not have been paying attention back then.  :)
> 
> > > +Example:
> > > +This example has a camera CMA node in reserved memory, which is then
> > > +referenced by the dmabuf-heap-cma node.
> > > +
> > > +
> > > +       reserved-memory {
> > > +               #address-cells = <2>;
> > > +               #size-cells = <2>;
> > > +               ranges;
> > > +               ...
> > > +               cma_camera: cma-camera {
> > > +                       compatible = "shared-dma-pool";
> > > +                       reg = <0x0 0x24C00000 0x0 0x4000000>;
> > > +                       reusable;
> > > +               };
> > > +               ...
> > > +       };
> > > +
> > > +       cma_heap {
> > > +               compatible = "dmabuf-heap-cma";
> > > +               memory-region = <&cma_camera>;
> >
> > Why the indirection here? Can't you just add a flag property to
> > reserved-memory nodes like we do to flag CMA nodes?
> 
> Happy to try. Do you mean like with the "reuasable" tag?  Or more like
> the "linux,cma-default" tag?

Probably like "linux,cma-default" as it is a hint for who to manage it 
rather than a characteristic of the region.

> Do you have a preference for the flag name here?

Not really.

> > As I suspected, it's because in patch 2 you're just abusing DT to
> > instantiate platform devices. We already support binding drivers to
> > reserved-memory nodes directly.
> 
> Sorry, one of those "when all you know how to do is hammer, everything
> looks like a nail" issues.
> Is there a specific example for binding drivers to reserved-memory
> nodes I can try to follow?

ramoops and I think there's a QCom driver.

Rob