linux-kernel - Re: [PATCH v8 06/34] dt-bindings: clock: tegra-car: Document new tegra-clocks sub-node

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Message-ID: <a5b942cb-1611-9ae1-6e89-4b68fdaf03e3@gmail.com>
Date:   Wed, 18 Aug 2021 19:57:04 +0300
From:   Dmitry Osipenko <digetx@...il.com>
To:     Thierry Reding <thierry.reding@...il.com>,
        Rob Herring <robh+dt@...nel.org>
Cc:     Jonathan Hunter <jonathanh@...dia.com>,
        Ulf Hansson <ulf.hansson@...aro.org>,
        Viresh Kumar <vireshk@...nel.org>,
        Stephen Boyd <sboyd@...nel.org>,
        Peter De Schrijver <pdeschrijver@...dia.com>,
        Mikko Perttunen <mperttunen@...dia.com>,
        Peter Chen <peter.chen@...nel.org>,
        Mark Brown <broonie@...nel.org>,
        Lee Jones <lee.jones@...aro.org>,
        Uwe Kleine-König <u.kleine-koenig@...gutronix.de>,
        Nishanth Menon <nm@...com>,
        Vignesh Raghavendra <vigneshr@...com>,
        Richard Weinberger <richard@....at>,
        Miquel Raynal <miquel.raynal@...tlin.com>,
        Lucas Stach <dev@...xeye.de>, Stefan Agner <stefan@...er.ch>,
        Adrian Hunter <adrian.hunter@...el.com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Michael Turquette <mturquette@...libre.com>,
        linux-kernel@...r.kernel.org, linux-tegra@...r.kernel.org,
        linux-pm@...r.kernel.org, linux-usb@...r.kernel.org,
        linux-staging@...ts.linux.dev, linux-spi@...r.kernel.org,
        linux-pwm@...r.kernel.org, linux-mtd@...ts.infradead.org,
        linux-mmc@...r.kernel.org, linux-media@...r.kernel.org,
        dri-devel@...ts.freedesktop.org, devicetree@...r.kernel.org,
        linux-clk@...r.kernel.org
Subject: Re: [PATCH v8 06/34] dt-bindings: clock: tegra-car: Document new
 tegra-clocks sub-node

18.08.2021 19:39, Thierry Reding пишет:
>> We don't have a platform device for CaR. I don't see how it's going to
>> work. We need to create a platform device for each RPM-capable clock
>> because that's how RPM works. The compatible string is required for
>> instantiating OF-devices from a node, otherwise we will have to
>> re-invent the OF core.
> I think we do have a platform device for CAR. It's just not bound
> against by the driver because these clock drivers are "special". But
> from other parts of the series you're already trying to fix that, at
> least partially.
> 
> But it doesn't seem right to create a platform device for each RPM-
> capable clock. Why do they need to be devices? They aren't, so why
> pretend? Is it that some API that we want to use here requires the
> struct device?

The "device" representation is internal to the kernel. It's okay to me
to have PLLs represented by a device, it's a distinct h/w by itself.

CCF supports managing of clock's RPM and it requires to have clock to be
backed by a device. That's what we are using here.

Please see
https://elixir.bootlin.com/linux/v5.14-rc6/source/drivers/clk/clk.c#L109

>>> Also, I don't think the tegra- prefix is necessary here. The parent node
>>> is already identified as Tegra via the compatible string.
>>>
>>> In the case of CAR, I'd imagine something like:
>>>
>>> 	clocks {
>>> 		sclk {
>>> 			operating-points-v2 = <&opp_table>;
>>> 			power-domains = <&domain>;
>>> 		};
>>> 	};
>>>
>>> Now you've only got the bare minimum in here that you actually add. All
>>> the other data that you used to have is simply derived from the parent.
>> 'clocks' is already a generic keyword in DT. It's probably not okay to
>> redefine it.
> "clocks" is not a generic keyword. It's the name of a property and given
> that we're talking about the clock provider here, it doesn't need a
> clocks property of its own, so it should be fine to use that for the
> node.

I'm curious what Rob thinks about it. Rob, does this sound okay to you?