linux-kernel - Re: [PATCH v2 3/4] PM: domains: Drop/restore performance state votes for devices at runtime PM

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Date:   Thu, 3 Jun 2021 15:25:38 +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 v2 3/4] PM: domains: Drop/restore performance state votes
 for devices at runtime PM

On 03-06-21, 11:34, 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>
> ---
> 
> Changes in v2:
> 	- Rebased.
> 	- A few minor cosmetic changes.
> 	- Deal with the error path in genpd_runtime_resume().
> 
> ---
>  drivers/base/power/domain.c | 27 +++++++++++++++++++++++++--
>  include/linux/pm_domain.h   |  1 +
>  2 files changed, 26 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/base/power/domain.c b/drivers/base/power/domain.c
> index ef25a5b18587..e5d97174c254 100644
> --- a/drivers/base/power/domain.c
> +++ b/drivers/base/power/domain.c
> @@ -400,6 +400,23 @@ static int genpd_set_performance_state(struct device *dev, unsigned int state)
>  	return ret;
>  }
>  
> +static int genpd_drop_performance_state(struct device *dev)

What about passing the state pointer here? that will simplify the
callers to just a call.

> +{
> +	unsigned int prev_state = dev_gpd_data(dev)->performance_state;
> +
> +	if (!genpd_set_performance_state(dev, 0))
> +		return prev_state;
> +
> +	return 0;
> +}
> +
> +static void genpd_restore_performance_state(struct device *dev,
> +					    unsigned int state)
> +{
> +	if (state)

I will skip this check, as we are checking it in
genpd_set_performance_state() anyway ?

> +		genpd_set_performance_state(dev, state);
> +}
> +
>  /**
>   * dev_pm_genpd_set_performance_state- Set performance state of device's power
>   * domain.
> @@ -842,7 +859,8 @@ 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;
> @@ -899,6 +917,7 @@ static int genpd_runtime_suspend(struct device *dev)
>  		return 0;
>  
>  	genpd_lock(genpd);
> +	gpd_data->rpm_pstate = genpd_drop_performance_state(dev);

So this will become:

	genpd_drop_performance_state(dev, &gpd_data->rpm_pstate);

and it can have return type of void.

-- 
viresh