linux-kernel - Re: [PATCH 3/3] arm64: dts: mediatek: mt8365-pumpkin: Add overlays for thp7312 cameras

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Message-ID: <169399810391.277971.691693692840899613@ping.linuxembedded.co.uk>
Date:   Wed, 06 Sep 2023 12:01:43 +0100
From:   Kieran Bingham <kieran.bingham@...asonboard.com>
To:     Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>,
        Laurent Pinchart <laurent.pinchart@...asonboard.com>
Cc:     Paul Elder <paul.elder@...asonboard.com>,
        linux-media@...r.kernel.org,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Conor Dooley <conor+dt@...nel.org>,
        Hans Verkuil <hverkuil-cisco@...all.nl>,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        linux-mediatek@...ts.infradead.org
Subject: Re: [PATCH 3/3] arm64: dts: mediatek: mt8365-pumpkin: Add overlays for thp7312 cameras

Quoting Laurent Pinchart (2023-09-06 10:35:31)
> On Wed, Sep 06, 2023 at 11:21:31AM +0200, Krzysztof Kozlowski wrote:
> > On 06/09/2023 11:00, Laurent Pinchart wrote:
> > >>> has a regulator@0. There are similar instances for clocks.
> > >>>
> > >>> I understand why it may not be a good idea, and how the root node is
> > >>> indeed not a bus. In some cases, those regulators and clocks are grouped
> > >>> in a regulators or clocks node that has a "simple-bus" compatible. I'm
> > >>> not sure if that's a good idea, but at least it should validate.
> > >>>
> > >>> What's the best practice for discrete board-level clocks and regulators
> > >>> in overlays ? How do we ensure that their node name will not conflict
> > >>> with the board to which the overlay is attached ?
> > >>
> > >> Top-level nodes (so under /) do not have unit addresses. If they have -
> > >> it's an error, because it is not a bus. Also, unit address requires reg.
> > >> No reg? No unit address. DTC reports this as warnings as well.
> > > 
> > > I agree with all that, but what's the recommended practice to add
> > > top-level clocks and regulators in overlays, in a way that avoids
> > > namespace clashes with the base board ?
> > 
> > Whether you use regulator@0 or regulator-0, you have the same chances of
> > clash.
> 
> No disagreement there. My question is whether there's a recommended
> practice to avoid clashes, or if it's an unsolved problem that gets
> ignored for now because there's only 36h in a day and there are more
> urgent things to do.

Should an overlay add these items to a simple-bus specific to that
overlay/device that is being supported?

That would 'namespace' the added fixed-clocks/fixed-regulators etc...

But maybe it's overengineering or mis-using the simple-bus.

And the items are still not on a 'bus' with an address - they just exist
on a presumably externally provided board....

--
Kieran