linux-kernel - Re: [PATCH V2 4/6] PM / domain: Register for PM QOS performance notifier

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Date:   Fri, 17 Feb 2017 15:54:58 -0800
From:   Kevin Hilman <khilman@...libre.com>
To:     Viresh Kumar <viresh.kumar@...aro.org>
Cc:     Rafael Wysocki <rjw@...ysocki.net>, ulf.hansson@...aro.org,
        Len Brown <len.brown@...el.com>, Pavel Machek <pavel@....cz>,
        linaro-kernel@...ts.linaro.org, linux-pm@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Vincent Guittot <vincent.guittot@...aro.org>,
        sboyd@...eaurora.org, nm@...com, robh+dt@...nel.org,
        lina.iyer@...aro.org, rnayak@...eaurora.org
Subject: Re: [PATCH V2 4/6] PM / domain: Register for PM QOS performance notifier

Viresh Kumar <viresh.kumar@...aro.org> writes:

> Some platforms have the capability to configure the performance state of
> their Power Domains. The performance levels are represented by positive
> integer values, a lower value represents lower performance state.
>
> This patch registers the power domain framework for PM QOS performance
> notifier in order to manage performance state of power domains.

It seems to me it doesm't just register, but actually keeps track of the
performance_state by always tracking the max.

> This also allows the power domain drivers to implement a
> ->set_performance_state() callback, which will be called by the power
> domain core from the notifier routine.
>
> Signed-off-by: Viresh Kumar <viresh.kumar@...aro.org>
> ---
>  drivers/base/power/domain.c | 98 ++++++++++++++++++++++++++++++++++++++++++++-
>  include/linux/pm_domain.h   |  5 +++
>  2 files changed, 101 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/base/power/domain.c b/drivers/base/power/domain.c
> index a73d79670a64..1158a07f92de 100644
> --- a/drivers/base/power/domain.c
> +++ b/drivers/base/power/domain.c
> @@ -367,6 +367,88 @@ static int genpd_dev_pm_qos_notifier(struct notifier_block *nb,
>  	return NOTIFY_DONE;
>  }
>  
> +static void update_domain_performance_state(struct generic_pm_domain *genpd,
> +					    int depth)
> +{
> +	struct generic_pm_domain_data *pd_data;
> +	struct generic_pm_domain *subdomain;
> +	struct pm_domain_data *pdd;
> +	unsigned int state = 0;
> +	struct gpd_link *link;
> +
> +	/* Traverse all devices within the domain */
> +	list_for_each_entry(pdd, &genpd->dev_list, list_node) {
> +		pd_data = to_gpd_data(pdd);
> +
> +		if (pd_data->performance_state > state)
> +			state = pd_data->performance_state;
> +	}

This seems to only update the state if it's bigger.  Maybe I'm missing
something here, but it seems like won't be able to lower the
performance_state after it's been raised?

> +	/* Traverse all subdomains within the domain */
> +	list_for_each_entry(link, &genpd->master_links, master_node) {
> +		subdomain = link->slave;
> +
> +		if (subdomain->performance_state > state)
> +			state = subdomain->performance_state;
> +	}

So subdomains are always assumed to influence the performance_state of
the parent domains?  Is that always the case?  I suspect this should be
probably be a reasonable default assumption, but maybe controlled with a
flag.

> +	if (genpd->performance_state == state)
> +		return;
> +
> +	genpd->performance_state = state;
> +
> +	if (genpd->set_performance_state) {
> +		genpd->set_performance_state(genpd, state);
> +		return;
> +	}

So is zero not a valid performance_state?  That doesn't seem quite right
to me, but either way, it should be documented.

> +	/* Propagate only if this domain has a single parent */

Why?  This limitation should be explained in the cover letter and
changelog.  I would also expect some sort of WARN here since this could
otherwise be a rather silent failures.

[...]

Kevin