Re: [PATCH v3 04/12] opp: Add dev_pm_opp_sync_regulators()

[Dmitry Osipenko]

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.

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.