Re: [PATCH 2/6] dt-bindings: display: msm: gmu: add optional ocmem property

[Rob Clark <robdclark-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>]

On Thu, Jun 20, 2019 at 7:14 PM Brian Masney <masneyb@onstation.org> wrote:
>
> On Wed, Jun 19, 2019 at 01:21:20PM -0700, Rob Clark wrote:
> > On Wed, Jun 19, 2019 at 1:17 PM Rob Herring <robh+dt@kernel.org> wrote:
> > >
> > > On Sun, Jun 16, 2019 at 7:29 AM Brian Masney <masneyb@onstation.org> wrote:
> > > >
> > > > Some A3xx and A4xx Adreno GPUs do not have GMEM inside the GPU core and
> > > > must use the On Chip MEMory (OCMEM) in order to be functional. Add the
> > > > optional ocmem property to the Adreno Graphics Management Unit bindings.
> > > >
> > > > Signed-off-by: Brian Masney <masneyb@onstation.org>
> > > > ---
> > > >  Documentation/devicetree/bindings/display/msm/gmu.txt | 4 ++++
> > > >  1 file changed, 4 insertions(+)
> > > >
> > > > diff --git a/Documentation/devicetree/bindings/display/msm/gmu.txt b/Documentation/devicetree/bindings/display/msm/gmu.txt
> > > > index 90af5b0a56a9..c746b95e95d4 100644
> > > > --- a/Documentation/devicetree/bindings/display/msm/gmu.txt
> > > > +++ b/Documentation/devicetree/bindings/display/msm/gmu.txt
> > > > @@ -31,6 +31,10 @@ Required properties:
> > > >  - iommus: phandle to the adreno iommu
> > > >  - operating-points-v2: phandle to the OPP operating points
> > > >
> > > > +Optional properties:
> > > > +- ocmem: phandle to the On Chip Memory (OCMEM) that's present on some Snapdragon
> > > > +         SoCs. See Documentation/devicetree/bindings/soc/qcom/qcom,ocmem.yaml.
> > >
> > > We already have a couple of similar properties. Lets standardize on
> > > 'sram' as that is what TI already uses.
> > >
> > > Also, is the whole OCMEM allocated to the GMU? If not you should have
> > > child nodes to subdivide the memory.
> > >
> >
> > iirc, downstream a large chunk of OCMEM is statically allocated for
> > GPU.. the remainder is dynamically allocated for different use-cases.
> > The upstream driver Brian is proposing only handles the static
> > allocation case
>
> It appears that the GPU expects to use a specific region of ocmem,
> specifically starting at 0. The freedreno driver allocates 1MB of
> ocmem on the Nexus 5 starting at ocmem address 0. As a test, I
> changed the starting address to 0.5MB and kmscube shows only half the
> cube, and four wide black bars across the screen:
>
> https://www.flickr.com/photos/masneyb/48100534381/
>
> > (and I don't think we have upstream support for the various audio and
> > video use-cases that used dynamic OCMEM allocation downstream)
>
> That's my understanding as well.
>
> > Although maybe we should still have a child node to separate the
> > statically and dynamically allocated parts?  I'm not sure what would
> > make the most sense..
>
> Given that the GPU is expecting a fixed address in ocmem, perhaps it
> makes sense to have the child node. How about this based on the
> sram/sram.txt bindings?
>
>   ocmem: ocmem@fdd00000 {
>     compatible = "qcom,msm8974-ocmem";
>
>     reg = <0xfdd00000 0x2000>, <0xfec00000 0x180000>;
>     reg-names = "ctrl", "mem";
>
>     clocks = <&rpmcc RPM_SMD_OCMEMGX_CLK>, <&mmcc OCMEMCX_OCMEMNOC_CLK>;
>     clock-names = "core", "iface";
>
>     gmu-sram@0 {
>       reg = <0x0 0x100000>;
>       pool;
>     };
>
>     misc-sram@0 {
>       reg = <0x100000 0x080000>;
>       export;
>     };
>   };
>
> I marked the misc pool as export since I've seen in the downstream ocmem
> sources a reference to their closed libsensors that runs in userspace.
>
> Looking at the sram bindings led me to the genalloc API
> (Documentation/core-api/genalloc.rst). I wonder if this is the way that
> this should be done?

won't claim to be a dt expert, but this seems somewhat sane..  maybe
drop the export until a use-case comes along for that.. or even the
entire second child node?  I guess that comes down to what robher and
others prefer, I can't really speculate too much about the non-gpu
use-cases for ocmem (or if they'll ever be upstream)

BR,
-R
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