linux-kernel - Re: [PATCH v1] dt-bindings: clock: convert rockchip,rk3188-cru.txt to YAML

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Date:   Thu, 31 Mar 2022 15:37:57 -0700
From:   Stephen Boyd <sboyd@...nel.org>
To:     Johan Jonker <jbx6244@...il.com>,
        Krzysztof Kozlowski <krzk@...nel.org>, heiko@...ech.de
Cc:     robh+dt@...nel.org, krzk+dt@...nel.org, mturquette@...libre.com,
        linux-clk@...r.kernel.org, devicetree@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        linux-rockchip@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1] dt-bindings: clock: convert rockchip,rk3188-cru.txt to YAML

Quoting Krzysztof Kozlowski (2022-03-25 00:31:25)
> On 25/03/2022 01:51, Stephen Boyd wrote:
> > Quoting Johan Jonker (2022-03-24 12:51:36)
> >> Hi Heiko, Krzysztof,
> >>
> >> Question for the Rockchip clock maintainer:
> >> What clock should be used here and other SoCs with several clock parents
> >> in the tree?
> >>
> >> The clock.yaml produces a lot off notifications like:
> >>
> >> /arch/arm/boot/dts/rk3036-evb.dtb: clock-controller@...00000: 'clocks'
> >> is a dependency of 'assigned-clocks'
> > 
> > 'clocks' is not a dependency of 'assigned-clocks'. The dt-schema should
> > be fixed to remove that requirement.
> 
> If the driver does not have any clock inputs ("clocks" property), why
> does it care about some clock frequencies and parents?

Because it's a clock provider itself. In this case I suspect because
this is a clock-controller node it was skipping describing some crystal
input though. Maybe it wants to configure the various PLLs in the
clock-controller for a particular board. I can imagine some node with
#clock-cells may want to configure the frequency of the clock outputs or
configure the clk parents for a certain board/SoC. In that case there
may not be any clocks property, but we still want to configure things.

> 
> The clocks is the logical dependency of assigned-clocks, because
> otherwise hardware description is not complete.

Sure, but also #clock-cells indicating that this is a clock-controller
itself means something. The existing bindings are what they are so
forcing bindings to be updated to comply with having a 'clocks' property
doesn't seem very nice.

> 
> What should be here for Rockhip? We had similar cases like this for many
> drivers, I was fixing some of Exynos as well. In my case usually the
> root/external clock was missing, so I supplied is as input clock to the
> clock controller.
> 

Can the schema consider either #clock-cells or clocks? I think that will
work for most cases. It would also be good to have a comment in the
schema or more detail around the definition of assigned-clocks in
bindings/clock/clock-bindings.txt that clocks or #clock-cells are
required. It would be super cool if assigned-clocks only applied if
#clock-cells was present, otherwise clocks property applies, but I doubt
we can do that anymore given how long the binding has been around.