linux-kernel - Re: [PATCH v8 01/34] opp: Add dev_pm_opp

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Date:   Mon, 23 Aug 2021 18:54:26 +0300
From:   Dmitry Osipenko <digetx@...il.com>
To:     Ulf Hansson <ulf.hansson@...aro.org>
Cc:     Viresh Kumar <viresh.kumar@...aro.org>,
        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>,
        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>,
        Rob Herring <robh+dt@...nel.org>,
        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-spi@...r.kernel.org,
        linux-pwm@...r.kernel.org, linux-mtd@...ts.infradead.org,
        linux-mmc <linux-mmc@...r.kernel.org>,
        Linux Media Mailing List <linux-media@...r.kernel.org>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        DTML <devicetree@...r.kernel.org>,
        linux-clk <linux-clk@...r.kernel.org>
Subject: Re: [PATCH v8 01/34] opp: Add dev_pm_opp_sync() helper

23.08.2021 13:46, Ulf Hansson пишет:
>>> ...
>>> dev_pm_opp_set_rate(rate)
>>> pm_runtime_get_noresume()
>>> pm_runtime_set_active()
>>> pm_runtime_enable()
>>> ...
>>> pm_runtime_put()
>>> ...
>>>
>>> We need to call genpd_set_performance_state() independently of whether
>>> the device is runtime suspended or not.
>>
>> I don't see where is the problem in yours example.
>>
>> pm_runtime_suspended() = false while RPM is disabled. When device is
>> resumed, the rpm_pstate=0, so it won't change the pstate on resume.
> 
> Yes, you are certainly correct, my bad! I mixed it up with
> pm_runtime_status_suspended(), which only cares about the status.
> 
> So, after a second thought, your suggestion sounds very much
> reasonable to me! I have also tried to consider all different
> scenarios, including the system suspend/resume path, but I think it
> should be fine.

It could be improved slightly to cover more cases.

> I also think that a patch like the above should be considered as a
> fix, because it actually fixes a problem, according to what I said in
> my earlier reply, below.
> 
> Fixes : 5937c3ce2122 ("PM: domains: Drop/restore performance state
> votes for devices at runtime PM").
> 
>>
>>> Although, it actually seems like good idea to update
>>> dev_gpd_data(dev)->rpm_pstate = state here, as to make sure
>>> genpd_runtime_resume() doesn't restore an old/invalid value that was
>>> saved while dropping the performance state vote for the device in
>>> genpd_runtime_suspend() earlier.
>>>
>>> Let me send a patch for this shortly, to close this window of a possible error.
>>
>> It will also remove the need to resume device just to change the clock
>> rate, like I needed to do it in the PWM patch of this series.
> 
> Do you want to send the patch formally? Or do you prefer it if I do it?

I'll send the patch.