linux-kernel - Re: [PATCH 2/3] PM: domains: Drop/restore performance state votes for devices at runtime PM

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Message-ID: <20210603023441.bs47nwtmskrdz2el@vireshk-i7>
Date:   Thu, 3 Jun 2021 08:04:41 +0530
From:   Viresh Kumar <viresh.kumar@...aro.org>
To:     Ulf Hansson <ulf.hansson@...aro.org>
Cc:     "Rafael J . Wysocki" <rjw@...ysocki.net>, linux-pm@...r.kernel.org,
        Dmitry Osipenko <digetx@...il.com>,
        Jonathan Hunter <jonathanh@...dia.com>,
        Thierry Reding <thierry.reding@...il.com>,
        Rajendra Nayak <rnayak@...eaurora.org>,
        Stephan Gerhold <stephan@...hold.net>,
        Roja Rani Yarubandi <rojay@...eaurora.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Stephen Boyd <sboyd@...nel.org>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/3] PM: domains: Drop/restore performance state votes
 for devices at runtime PM

On 02-06-21, 12:12, Ulf Hansson wrote:
> A subsystem/driver that need to manage OPPs for its device, should
> typically drop its vote for the OPP when the device becomes runtime
> suspended. In this way, the corresponding aggregation of the performance
> state votes that is managed in genpd for the attached PM domain, may find
> that the aggregated vote can be decreased. Hence, it may allow genpd to set
> the lower performance state for the PM domain, thus avoiding to waste
> energy.
> 
> To accomplish this, typically a subsystem/driver would need to call
> dev_pm_opp_set_rate|opp() for its device from its ->runtime_suspend()
> callback, to drop the vote for the OPP. Accordingly, it needs another call
> to dev_pm_opp_set_rate|opp() to restore the vote for the OPP from its
> ->runtime_resume() callback.
> 
> To avoid boilerplate code in subsystems/driver to deal with these things,
> let's instead manage this internally in genpd.
> 
> Signed-off-by: Ulf Hansson <ulf.hansson@...aro.org>
> ---
>  drivers/base/power/domain.c | 21 +++++++++++++++++++--
>  include/linux/pm_domain.h   |  1 +
>  2 files changed, 20 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/base/power/domain.c b/drivers/base/power/domain.c
> index a3b6e751f366..81b9d4652b90 100644
> --- a/drivers/base/power/domain.c
> +++ b/drivers/base/power/domain.c
> @@ -397,6 +397,18 @@ static int genpd_set_performance_state(struct device *dev, unsigned int state)
>  	return ret;
>  }
>  
> +static int genpd_drop_performance_state(struct device *dev)
> +{
> +	struct generic_pm_domain_data *gpd_data = dev_gpd_data(dev);
> +	unsigned int prev_state;
> +
> +	prev_state = gpd_data->performance_state;
> +	if (prev_state && !genpd_set_performance_state(dev, 0))

What about adding this prev_state check in
genpd_set_performance_state() itself ? We already have one for the
genpd in _genpd_set_performance_state(), why not one for the device ?

> +		return prev_state;
> +
> +	return 0;

Hmm, we will return 0 in case genpd_set_performance_state() fails,
which will make us set the state to 0 again on resume. Maybe add a
comment for this somewhere ?

> +}
> +
>  /**
>   * dev_pm_genpd_set_performance_state- Set performance state of device's power
>   * domain.
> @@ -839,7 +851,8 @@ static int genpd_runtime_suspend(struct device *dev)
>  {
>  	struct generic_pm_domain *genpd;
>  	bool (*suspend_ok)(struct device *__dev);
> -	struct gpd_timing_data *td = &dev_gpd_data(dev)->td;
> +	struct generic_pm_domain_data *gpd_data = dev_gpd_data(dev);
> +	struct gpd_timing_data *td = &gpd_data->td;
>  	bool runtime_pm = pm_runtime_enabled(dev);
>  	ktime_t time_start;
>  	s64 elapsed_ns;
> @@ -896,6 +909,7 @@ static int genpd_runtime_suspend(struct device *dev)
>  		return 0;
>  
>  	genpd_lock(genpd);
> +	gpd_data->rpm_saved_pstate = genpd_drop_performance_state(dev);
>  	genpd_power_off(genpd, true, 0);
>  	genpd_unlock(genpd);
>  
> @@ -913,7 +927,8 @@ static int genpd_runtime_suspend(struct device *dev)
>  static int genpd_runtime_resume(struct device *dev)
>  {
>  	struct generic_pm_domain *genpd;
> -	struct gpd_timing_data *td = &dev_gpd_data(dev)->td;
> +	struct generic_pm_domain_data *gpd_data = dev_gpd_data(dev);
> +	struct gpd_timing_data *td = &gpd_data->td;
>  	bool runtime_pm = pm_runtime_enabled(dev);
>  	ktime_t time_start;
>  	s64 elapsed_ns;
> @@ -937,6 +952,8 @@ static int genpd_runtime_resume(struct device *dev)
>  
>  	genpd_lock(genpd);
>  	ret = genpd_power_on(genpd, 0);
> +	if (!ret && gpd_data->rpm_saved_pstate)
> +		genpd_set_performance_state(dev, gpd_data->rpm_saved_pstate);
>  	genpd_unlock(genpd);
>  
>  	if (ret)
> diff --git a/include/linux/pm_domain.h b/include/linux/pm_domain.h
> index dfcfbcecc34b..c3d6c15788a3 100644
> --- a/include/linux/pm_domain.h
> +++ b/include/linux/pm_domain.h
> @@ -198,6 +198,7 @@ struct generic_pm_domain_data {
>  	struct notifier_block *power_nb;
>  	int cpu;
>  	unsigned int performance_state;
> +	unsigned int rpm_saved_pstate;
>  	ktime_t	next_wakeup;
>  	void *data;
>  };
> -- 
> 2.25.1

-- 
viresh