[PATCH 1/7] drm/vc4: Add devicetree bindings for VC4.

Eric Anholt eric at anholt.net
Mon Aug 17 11:30:14 PDT 2015

Stephen Warren <swarren at wwwdotorg.org> writes:

> On 08/12/2015 06:56 PM, Eric Anholt wrote:
>> Signed-off-by: Eric Anholt <eric at anholt.net>
> This one definitely needs a patch description, since someone might not
> know what a VC4 is, and "git log" won't show the text from the binding
> doc itself. I'd suggest adding the initial paragraph of the binding doc
> as the patch description, or more.
>> diff --git a/Documentation/devicetree/bindings/gpu/brcm,bcm-vc4.txt b/Documentation/devicetree/bindings/gpu/brcm,bcm-vc4.txt

>> +- hvss:		List of references to HVS video scalers
>> +- encoders:	List of references to output encoders (HDMI, SDTV)
> Would it make sense to make all those nodes child node of the vc4
> object. That way, there's no need to have these lists of objects; they
> can be automatically built up as the DT is enumerated. I know that e.g.
> the NVIDIA Tegra host1x binding works this way, and I think it may have
> been inspired by other similar cases.

I've looked at tegra, and the component system used by msm appears to be
nicer than it.  To follow tegra's model, it looks like I need to build
this extra bus thing corresponding to host1x that is effectively the
drivers/base/component.c code, so that I can get at vc4's structure from
the component drivers.

> Of course, this is only appropriate if the HW modules really are
> logically children of the VC4 HW module. Perhaps they aren't. If they
> aren't though, I wonder what this "vc4" module actually represents in HW?

It's the subsystem, same as we use a subsystem node for msm, sti,
rockchip, imx, and exynos.  This appears to be the common model of how
the collection of graphics-related components is represented in the DT.
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