[PATCH 02/12] drm/etnaviv: add devicetree bindings

[Rob Herring]

On Fri, Dec 4, 2015 at 10:41 AM, Lucas Stach <l.stach at pengutronix.de> wrote:
> Am Freitag, den 04.12.2015, 10:29 -0600 schrieb Rob Herring:
>> On Fri, Dec 04, 2015 at 02:59:54PM +0100, Lucas Stach wrote:
>> > Etnaviv follows the same priciple as imx-drm to have a virtual
>> > master device node to bind all the individual GPU cores together
>> > into one DRM device.
>> >
>> > Signed-off-by: Lucas Stach <l.stach at pengutronix.de>
>> > ---
>> >  .../bindings/display/etnaviv/etnaviv-drm.txt       | 46 ++++++++++++++++++++++
>> >  1 file changed, 46 insertions(+)
>> >  create mode 100644 Documentation/devicetree/bindings/display/etnaviv/etnaviv-drm.txt
>> >
>> > diff --git a/Documentation/devicetree/bindings/display/etnaviv/etnaviv-drm.txt b/Documentation/devicetree/bindings/display/etnaviv/etnaviv-drm.txt
>> > new file mode 100644
>> > index 000000000000..19fde29dc1d7
>> > --- /dev/null
>> > +++ b/Documentation/devicetree/bindings/display/etnaviv/etnaviv-drm.txt
>> > @@ -0,0 +1,46 @@
>> > +Etnaviv DRM master device
>> > +================================
>> > +
>> > +The Etnaviv DRM master device is a virtual device needed to list all
>> > +Vivante GPU cores that comprise the GPU subsystem.
>> > +
>> > +Required properties:
>> > +- compatible: Should be one of
>> > +    "fsl,imx-gpu-subsystem"
>> > +    "marvell,dove-gpu-subsystem"
>> > +- cores: Should contain a list of phandles pointing to Vivante GPU devices
>> > +
>> > +example:
>> > +
>> > +gpu-subsystem {
>> > +   compatible = "fsl,imx-gpu-subsystem";
>> > +   cores = <&gpu_2d>, <&gpu_3d>;
>> > +};
>>
>> Yeah, I'm not really a fan of doing this simply because DRM wants 1
>> driver.
>>
> I'm aware of that, but I don't see much value in kicking this discussion
> around for every DRM driver submission. This is the binding that has
> emerged from a lengthy discussion at KS 2013 in Edinburgh and at least
> allows us to standardize on _something_. Also ALSA does a similar thing
> to bind codecs and CPU interfaces together.

This case is quite different though I think. The ALSA case and other
DRM cases are ones that have inter-dependencies between the blocks
(e.g. some sort of h/w connection). What is the inter-dependency here?

Doing this way has also been found to be completely unnecessary and
removed in recent DRM driver reviews. Admittedly, those are cases
where one device can be the master of the others. For 2 parallel
devices, I don't have an alternative other than question why they need
to be a single driver.


>> > +Vivante GPU core devices
>> > +====================
>> > +
>> > +Required properties:
>> > +- compatible: Should be "vivante,gc"
>>
>> This should at least have the specific cores listed like gc-5000 or
>> whatever the numbering is. As is, I can't even tell if this a 2d or 3d
>> core.
>>
> There is really no need for this. The cores have identification
> registers that are much more accurate than what we could describe with a
> compatible value. So using a more specific compatible just provides
> redundant (and possibly wrong) information.
>
>> Also, it probably should have an SOC specific property to deal with SOC
>> specific configuration or integration.
>>
> Same as above really. Parts of the identification registers are
> different for each SoC integration, even if it's the same IP core, so we
> can just derive any needed driver behavior differences from that.

The h/w designers must have had a clue about s/w. First time for
everything... ;)

Ok, please just add a note to the binding why a more specific
compatible is not needed in this case.

Rob