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

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Message-ID: <20191030132932.GA7292@bogus>
Date:   Wed, 30 Oct 2019 08:29:32 -0500
From:   Rob Herring <robh@...nel.org>
To:     John Stultz <john.stultz@...aro.org>
Cc:     Rob Herring <rob.e.herring@...il.com>,
        lkml <linux-kernel@...r.kernel.org>,
        Mark Rutland <mark.rutland@....com>,
        Laura Abbott <labbott@...hat.com>,
        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>,
        "Andrew F . Davis" <afd@...com>, Chenbo Feng <fengc@...gle.com>,
        Alistair Strachan <astrachan@...gle.com>,
        Sandeep Patil <sspatil@...gle.com>,
        Hridya Valsaraju <hridya@...gle.com>,
        devicetree <devicetree@...r.kernel.org>,
        dri-devel <dri-devel@...ts.freedesktop.org>
Subject: Re: [RFC][PATCH 1/3] dt-bindings: dma-buf: heaps: Describe CMA
 regions to be added to dmabuf heaps interface.

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@...il.com> wrote:
> >
> > On Fri, Oct 25, 2019 at 5:51 PM John Stultz <john.stultz@...aro.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