linux-kernel - Re: [PATCH v13 06/35] clk: tegra: Support runtime PM and power domain

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Message-ID: <81ce6f35-acb0-fe34-1efc-537c058a2160@gmail.com>
Date:   Thu, 7 Oct 2021 13:36:39 +0300
From:   Dmitry Osipenko <digetx@...il.com>
To:     Ulf Hansson <ulf.hansson@...aro.org>
Cc:     Thierry Reding <thierry.reding@...il.com>,
        Jonathan Hunter <jonathanh@...dia.com>,
        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>,
        Lee Jones <lee.jones@...aro.org>,
        Uwe Kleine-König <u.kleine-koenig@...gutronix.de>,
        Nishanth Menon <nm@...com>,
        Adrian Hunter <adrian.hunter@...el.com>,
        Michael Turquette <mturquette@...libre.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-tegra <linux-tegra@...r.kernel.org>,
        Linux PM <linux-pm@...r.kernel.org>,
        Linux USB List <linux-usb@...r.kernel.org>,
        linux-staging@...ts.linux.dev, linux-pwm@...r.kernel.org,
        linux-mmc <linux-mmc@...r.kernel.org>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        DTML <devicetree@...r.kernel.org>,
        linux-clk <linux-clk@...r.kernel.org>,
        Mark Brown <broonie@...nel.org>,
        Vignesh Raghavendra <vigneshr@...com>,
        Richard Weinberger <richard@....at>,
        Miquel Raynal <miquel.raynal@...tlin.com>,
        Lucas Stach <dev@...xeye.de>, Stefan Agner <stefan@...er.ch>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        David Heidelberg <david@...t.cz>
Subject: Re: [PATCH v13 06/35] clk: tegra: Support runtime PM and power domain

07.10.2021 12:18, Ulf Hansson пишет:
>> Please let me iterate once again. The problem we currently have is that
>> clock may be enabled during NOIRQ time. In order to enable clock, it
>> needs to be prepared. In order to prepare clock, the clock's device
>> needs to be runtime-resumed. The runtime PM is unavailable at the NOIRQ
>> time.
>>
>> To solve this problem we need to prepare clock beforehand.
>>
>> The clock will stay prepared during suspend, but this is not a problem
>> since all the clocks we care about don't require high voltage and
>> voltage is guaranteed to be bumped high during suspend by Tegra's
>> regulator-coupler driver anyways.
>>
>> So everything we need to do is to keep clocks prepared. There are two
>> options how to do that:
>>
>> [1] this patch which explicitly prepares clocks using clk API.
>>
>> [2] Use runtime PM API, like this:
>>
>> static const struct dev_pm_ops tegra_clock_pm = {
>>         SET_SYSTEM_SLEEP_PM_OPS(pm_runtime_resume_and_get, pm_runtime_put)
>> };
>>
>> Ulf, are you now okay with the current variant [1] of the patch or you
>> prefer the second [2] option more?
> I prefer option [2]. The clock_prepare|unprepare() thingy in option
> [1], looks more like an odd workaround to me.
> 
> Does that make sense to you as well?

I don't have a strong preference since both variants give the same
effect. I'll keep testing option [2] and will use it in the next version
if no problem will be found. Thank you!