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SubjectRe: [PATCH v10 3/6] PM / Domains: make governor select deepest state
Hi Zhaoyang,


>> @@ -209,14 +186,52 @@ static bool default_power_down_ok(struct dev_pm_domain *pd)
>> * The difference between the computed minimum subdomain or device off
>> * time and the time needed to turn the domain on is the maximum
>> * theoretical time this domain can spend in the "off" state.
>> - * Use the only available state, until multiple state support is added
>> - * to the governor.
>> */
>> genpd->max_off_time_ns = min_off_time_ns -
>> - genpd->states[0].power_on_latency_ns;
>> + genpd->states[state].power_on_latency_ns;
>> return true;
>> }
> [question]: Does it mean that the sleep level is just decided by
> comparing the pre-configure on_off time with the gpd_timing_data? How
> about the next timer event which affect the sleep depth on cpuidle
> framework?



There are a couple of patches on the list ill try to summarize
what i understand, Lina, Marc please correct me if im wrong!

I did this patches thinking generally about devices in a power domain
and not so much about a cpu. So these patches are not aimed at replacing
cpuidle, but were meant for power domains that may have intermediate
states, for example some logic may be implemented with retention flip-flops.

There is the proposal by Lina [1] to add cpus clusters to powerdomins
and by Marc[2] that tie cluster idle states to the powerdomain handler.
but i think the effort here is to complement cpuidle rather than to
replace it.

regards
Axel

1. https://lwn.net/Articles/653579/
2. https://lwn.net/Articles/658461/

>>
>> +static bool default_power_down_ok(struct dev_pm_domain *pd)
>> +{
>> + struct generic_pm_domain *genpd = pd_to_genpd(pd);
>> + unsigned int last_state_idx = genpd->state_count - 1;
>> + struct gpd_link *link;
>> + bool retval = false;
>> + unsigned int i;
>> +
>> + /*
>> + * if there was no change on max_off_time, we can return the
>> + * cached value and we dont need to find a new target_state
>> + */
>> + if (!genpd->max_off_time_changed)
>> + return genpd->cached_power_down_ok;
>> +
>> + /*
>> + * We have to invalidate the cached results for the masters, so
>> + * use the observation that default_power_down_ok() is not
>> + * going to be called for any master until this instance
>> + * returns.
>> + */
>> + list_for_each_entry(link, &genpd->slave_links, slave_node)
>> + link->master->max_off_time_changed = true;
>> +
>> + genpd->max_off_time_ns = -1;
>> + genpd->max_off_time_changed = false;
>> +
>> + /* find a state to power down to, starting from the deepest */
>> + for (i = 0; i < genpd->state_count; i++) {
>> + if (power_down_ok_for_state(pd, last_state_idx - i)) {
>> + genpd->state_idx = last_state_idx - i;
>> + retval = true;
>> + break;
>> + }
>> + }
>> +
>> + genpd->cached_power_down_ok = retval;
>> + return retval;
>> +}
>> +
>> static bool always_on_power_down_ok(struct dev_pm_domain *domain)
>> {
>> return false;
> [question]How the TICK_NOHZ treated if we substitute cpuidle framework
> with this one?
>> --
>> 2.4.5
>>
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