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

Kevin Hilman
2017-02-18T00:03:19Z

Viresh Kumar <viresh.kumar@linaro.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@linaro.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