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

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Date:   Wed, 6 Sep 2023 14:14:29 +0300
From:   Laurent Pinchart <laurent.pinchart@...asonboard.com>
To:     Kieran Bingham <kieran.bingham@...asonboard.com>
Cc:     Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>,
        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

On Wed, Sep 06, 2023 at 12:01:43PM +0100, Kieran Bingham wrote:
> 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.

You would still need to name the node that groups the regulators and
clocks in a way that wouldn't clash between multiple overlays and the
base board. It would be nice to have nodes that are "private" to an
overlay.

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

-- 
Regards,

Laurent Pinchart