linux-kernel - Re: [PATCH v10 1/8] opp: Add dev_pm_opp_get

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Date:   Wed, 1 Sep 2021 08:43:40 +0300
From:   Dmitry Osipenko <digetx@...il.com>
To:     Viresh Kumar <viresh.kumar@...aro.org>
Cc:     Thierry Reding <thierry.reding@...il.com>,
        Jonathan Hunter <jonathanh@...dia.com>,
        Ulf Hansson <ulf.hansson@...aro.org>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Kevin Hilman <khilman@...nel.org>,
        Viresh Kumar <vireshk@...nel.org>,
        Stephen Boyd <sboyd@...nel.org>, Nishanth Menon <nm@...com>,
        linux-kernel@...r.kernel.org, linux-tegra@...r.kernel.org,
        linux-pm@...r.kernel.org
Subject: Re: [PATCH v10 1/8] opp: Add dev_pm_opp_get_current()

01.09.2021 07:39, Viresh Kumar пишет:
> On 31-08-21, 16:54, Dmitry Osipenko wrote:
>> Add dev_pm_opp_get_current() helper that returns OPP corresponding
>> to the current clock rate of a device.
>>
>> Signed-off-by: Dmitry Osipenko <digetx@...il.com>
>> ---
>>  drivers/opp/core.c     | 43 +++++++++++++++++++++++++++++++++++++++---
>>  include/linux/pm_opp.h |  6 ++++++
>>  2 files changed, 46 insertions(+), 3 deletions(-)
>>
>> diff --git a/drivers/opp/core.c b/drivers/opp/core.c
>> index 04b4691a8aac..dde8a5cc948c 100644
>> --- a/drivers/opp/core.c
>> +++ b/drivers/opp/core.c
>> @@ -939,7 +939,7 @@ static int _set_required_opps(struct device *dev,
>>  	return ret;
>>  }
>>  
>> -static void _find_current_opp(struct device *dev, struct opp_table *opp_table)
>> +static struct dev_pm_opp *_find_current_opp(struct opp_table *opp_table)
>>  {
>>  	struct dev_pm_opp *opp = ERR_PTR(-ENODEV);
>>  	unsigned long freq;
>> @@ -949,6 +949,18 @@ static void _find_current_opp(struct device *dev, struct opp_table *opp_table)
>>  		opp = _find_freq_ceil(opp_table, &freq);
>>  	}
>>  
>> +	return opp;
>> +}
>> +
>> +static void _find_and_set_current_opp(struct opp_table *opp_table)
>> +{
>> +	struct dev_pm_opp *opp;
>> +
>> +	if (opp_table->current_opp)
>> +		return;
> 
> Why move this from caller as well ?

To make code cleaner.

>> +
>> +	opp = _find_current_opp(opp_table);
>> +
>>  	/*
>>  	 * Unable to find the current OPP ? Pick the first from the list since
>>  	 * it is in ascending order, otherwise rest of the code will need to
> 
> If we aren't able to find current OPP based on current freq, then this
> picks the first value from the list. Why shouldn't this be done in
> your case as well ?

You will get OPP which corresponds to the lowest freq, while h/w runs on
unsupported high freq. This may end with a tragedy.

>> @@ -1002,8 +1014,7 @@ static int _set_opp(struct device *dev, struct opp_table *opp_table,
>>  		return _disable_opp_table(dev, opp_table);
>>  
>>  	/* Find the currently set OPP if we don't know already */
>> -	if (unlikely(!opp_table->current_opp))
>> -		_find_current_opp(dev, opp_table);
>> +	_find_and_set_current_opp(opp_table);
>>  
>>  	old_opp = opp_table->current_opp;
>>  
>> @@ -2931,3 +2942,29 @@ int dev_pm_opp_sync_regulators(struct device *dev)
>>  	return ret;
>>  }
>>  EXPORT_SYMBOL_GPL(dev_pm_opp_sync_regulators);
>> +
>> +/**
>> + * dev_pm_opp_get_current() - Get current OPP
>> + * @dev:	device for which we do this operation
>> + *
>> + * Get current OPP of a device based on current clock rate or by other means.
>> + *
>> + * Return: pointer to 'struct dev_pm_opp' on success and errorno otherwise.
>> + */
>> +struct dev_pm_opp *dev_pm_opp_get_current(struct device *dev)
>> +{
>> +	struct opp_table *opp_table;
>> +	struct dev_pm_opp *opp;
>> +
>> +	opp_table = _find_opp_table(dev);
>> +	if (IS_ERR(opp_table))
>> +		return ERR_CAST(opp_table);
>> +
>> +	opp = _find_current_opp(opp_table);
> 
> This should not just go find the OPP based on current freq. This first
> needs to check if curret_opp is set or not. If set, then just return
> it, else run the _find_current_opp() function and update the
> current_opp pointer as well.
> 

Alright, I'll change it.