linux-kernel - Re: [PATCH] opp: Prepare for ->set_opp() helper to work without regulators

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Date:   Wed, 20 Jan 2021 13:09:12 +0530
From:   Viresh Kumar <viresh.kumar@...aro.org>
To:     Dmitry Osipenko <digetx@...il.com>
Cc:     Viresh Kumar <vireshk@...nel.org>, Nishanth Menon <nm@...com>,
        Stephen Boyd <sboyd@...nel.org>, linux-pm@...r.kernel.org,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Rafael Wysocki <rjw@...ysocki.net>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] opp: Prepare for ->set_opp() helper to work without
 regulators

On 19-01-21, 20:16, Dmitry Osipenko wrote:
> 19.01.2021 09:35, Viresh Kumar пишет:
> > +	mutex_lock(&opp_table->lock);
> > +	opp_table->set_opp_data = data;
> > +	if (opp_table->sod_supplies) {
> > +		data->old_opp.supplies = opp_table->sod_supplies;
> > +		data->new_opp.supplies = opp_table->sod_supplies +
> > +					 opp_table->regulator_count;
> > +	}
> > +	mutex_unlock(&opp_table->lock);
> 
> Why do we need all these locks in this patch?

In case dev_pm_opp_set_regulators() and
dev_pm_opp_register_set_opp_helper() get called at the same time.
Which can actually happen, though is a corner case.

> The OPP API isn't thread-safe, these locks won't make the API
> thread-safe.

I am not sure what you mean by that, can you please explain ?

> At least both sod_supplies and set_opp() pointers should be
> set and unset under the lock.

The ->set_opp pointer isn't getting used for a comparison and so
putting that inside a lock won't get us anything. We are only using
set_opp_data and sod_supplies for comparison at both the places and so
they need to be updated within the lock.

-- 
viresh