linux-kernel - Re: [PATCH 1/7] drm/vc4: Add devicetree bindings for VC4.

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Date:	Mon, 24 Aug 2015 08:47:00 -0500
From:	Rob Herring <robherring2@...il.com>
To:	Eric Anholt <eric@...olt.net>
Cc:	Stephen Warren <swarren@...dotorg.org>,
	dri-devel <dri-devel@...ts.freedesktop.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	Lee Jones <lee@...nel.org>,
	linux-rpi-kernel@...ts.infradead.org,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/7] drm/vc4: Add devicetree bindings for VC4.

On Mon, Aug 17, 2015 at 1:30 PM, Eric Anholt <eric@...olt.net> wrote:
> Stephen Warren <swarren@...dotorg.org> writes:
>
>> On 08/12/2015 06:56 PM, Eric Anholt wrote:
>>> Signed-off-by: Eric Anholt <eric@...olt.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.

I think most of these bindings are wrong. They are grouped together
because that is what DRM wants not because that reflects the h/w. So
convince me this is one block, not that it is what other people do.

Rob
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