linux-kernel - Re: [PATCH v3 04/12] opp: Add dev_pm_opp_sync

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Message-ID: <20210119045827.2645gk6vabubehuh@vireshk-i7>
Date:   Tue, 19 Jan 2021 10:28:27 +0530
From:   Viresh Kumar <viresh.kumar@...aro.org>
To:     Dmitry Osipenko <digetx@...il.com>
Cc:     Thierry Reding <thierry.reding@...il.com>,
        Jonathan Hunter <jonathanh@...dia.com>,
        Mark Brown <broonie@...nel.org>,
        Liam Girdwood <lgirdwood@...il.com>,
        Ulf Hansson <ulf.hansson@...aro.org>,
        Peter Geis <pgwipeout@...il.com>,
        Nicolas Chauvet <kwizart@...il.com>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Kevin Hilman <khilman@...nel.org>,
        Peter De Schrijver <pdeschrijver@...dia.com>,
        Viresh Kumar <vireshk@...nel.org>,
        Stephen Boyd <sboyd@...nel.org>, Nishanth Menon <nm@...com>,
        Yangtao Li <tiny.windzz@...il.com>,
        Matt Merhar <mattmerhar@...tonmail.com>,
        linux-kernel@...r.kernel.org, linux-tegra@...r.kernel.org,
        linux-pm@...r.kernel.org
Subject: Re: [PATCH v3 04/12] opp: Add dev_pm_opp_sync_regulators()

On 18-01-21, 21:35, Dmitry Osipenko wrote:
> 18.01.2021 11:20, Viresh Kumar пишет:
> >> +int dev_pm_opp_sync_regulators(struct device *dev)
> >> +{
> >> +	struct opp_table *opp_table;
> >> +	struct regulator *reg;
> >> +	int i, ret = 0;
> >> +
> >> +	/* Device may not have OPP table */
> >> +	opp_table = _find_opp_table(dev);
> >> +	if (IS_ERR(opp_table))
> >> +		return 0;
> >> +
> >> +	/* Regulator may not be required for the device */
> >> +	if (!opp_table->regulators)
> >> +		goto put_table;
> >> +
> >> +	mutex_lock(&opp_table->lock);
> > What exactly do you need this lock for ?
> 
> It is needed for protecting simultaneous invocations of
> dev_pm_opp_sync_regulators() and dev_pm_opp_set_voltage().
> 
> The sync_regulators() should be invoked only after completion of the
> set_voltage() in a case of Tegra power domain driver since potentially
> both could be running in parallel. For example device driver may be
> changing performance state in a work thread, while PM domain state is
> syncing.

I think just checking the 'enabled' flag should be enough here (you may need a
lock for it though, but the lock should cover only the area it is supposed to
cover and nothing else.

> But maybe it will be better to move the protection to the PM driver
> since we're focused on sync_regulators() and set_voltage() here, but
> there are other OPP API functions which use regulators. I'll need to
> take a closer look at it.

-- 
viresh