![Rafael J. Wysocki](/assets/img/avatar_default.png)
The special value of 0 for device resume latency PM QoS means
"no restriction", but there are two problems with that.
First, device resume latency PM QoS requests with 0 as the
value are always put in front of requests with positive
values in the priority lists used internally by the PM QoS
framework, causing 0 to be chosen as an effective constraint
value. However, that 0 is then interpreted as "no restriction"
effectively overriding the other requests with specific
restrictions which is incorrect.
Second, the users of device resume latency PM QoS have no
way to specify that *any* resume latency at all should be
avoided, which is an artificial limitation in general.
To address these issues, modify device resume latency PM QoS to
use S32_MAX as the "no constraint" value and 0 as the "no
latency at all" one and rework its users (the cpuidle menu
governor, the genpd QoS governor and the runtime PM framework)
to follow these changes.
Also add a special "n/a" value to the corresponding user space I/F
to allow user space to indicate that it cannot accept any resume
latencies at all for the given device.
Fixes: 85dc0b8a40
(PM / QoS: Make it possible to expose PM QoS latency constraints)
Link: https://bugzilla.kernel.org/show_bug.cgi?id=197323
Reported-by: Reinette Chatre <reinette.chatre@intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Tested-by: Reinette Chatre <reinette.chatre@intel.com>
Tested-by: Geert Uytterhoeven <geert+renesas@glider.be>
Tested-by: Tero Kristo <t-kristo@ti.com>
Reviewed-by: Ramesh Thomas <ramesh.thomas@intel.com>
260 lines
7.2 KiB
C
260 lines
7.2 KiB
C
/*
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* drivers/base/power/domain_governor.c - Governors for device PM domains.
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*
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* Copyright (C) 2011 Rafael J. Wysocki <rjw@sisk.pl>, Renesas Electronics Corp.
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*
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* This file is released under the GPLv2.
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*/
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#include <linux/kernel.h>
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#include <linux/pm_domain.h>
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#include <linux/pm_qos.h>
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#include <linux/hrtimer.h>
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static int dev_update_qos_constraint(struct device *dev, void *data)
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{
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s64 *constraint_ns_p = data;
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s64 constraint_ns;
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if (dev->power.subsys_data && dev->power.subsys_data->domain_data) {
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/*
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* Only take suspend-time QoS constraints of devices into
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* account, because constraints updated after the device has
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* been suspended are not guaranteed to be taken into account
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* anyway. In order for them to take effect, the device has to
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* be resumed and suspended again.
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*/
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constraint_ns = dev_gpd_data(dev)->td.effective_constraint_ns;
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} else {
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/*
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* The child is not in a domain and there's no info on its
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* suspend/resume latencies, so assume them to be negligible and
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* take its current PM QoS constraint (that's the only thing
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* known at this point anyway).
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*/
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constraint_ns = dev_pm_qos_read_value(dev);
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constraint_ns *= NSEC_PER_USEC;
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}
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if (constraint_ns < *constraint_ns_p)
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*constraint_ns_p = constraint_ns;
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return 0;
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}
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/**
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* default_suspend_ok - Default PM domain governor routine to suspend devices.
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* @dev: Device to check.
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*/
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static bool default_suspend_ok(struct device *dev)
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{
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struct gpd_timing_data *td = &dev_gpd_data(dev)->td;
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unsigned long flags;
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s64 constraint_ns;
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dev_dbg(dev, "%s()\n", __func__);
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spin_lock_irqsave(&dev->power.lock, flags);
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if (!td->constraint_changed) {
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bool ret = td->cached_suspend_ok;
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spin_unlock_irqrestore(&dev->power.lock, flags);
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return ret;
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}
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td->constraint_changed = false;
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td->cached_suspend_ok = false;
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td->effective_constraint_ns = 0;
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constraint_ns = __dev_pm_qos_read_value(dev);
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spin_unlock_irqrestore(&dev->power.lock, flags);
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if (constraint_ns == 0)
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return false;
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constraint_ns *= NSEC_PER_USEC;
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/*
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* We can walk the children without any additional locking, because
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* they all have been suspended at this point and their
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* effective_constraint_ns fields won't be modified in parallel with us.
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*/
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if (!dev->power.ignore_children)
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device_for_each_child(dev, &constraint_ns,
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dev_update_qos_constraint);
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if (constraint_ns == PM_QOS_RESUME_LATENCY_NO_CONSTRAINT_NS) {
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/* "No restriction", so the device is allowed to suspend. */
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td->effective_constraint_ns = PM_QOS_RESUME_LATENCY_NO_CONSTRAINT_NS;
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td->cached_suspend_ok = true;
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} else if (constraint_ns == 0) {
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/*
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* This triggers if one of the children that don't belong to a
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* domain has a zero PM QoS constraint and it's better not to
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* suspend then. effective_constraint_ns is zero already and
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* cached_suspend_ok is false, so bail out.
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*/
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return false;
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} else {
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constraint_ns -= td->suspend_latency_ns +
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td->resume_latency_ns;
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/*
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* effective_constraint_ns is zero already and cached_suspend_ok
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* is false, so if the computed value is not positive, return
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* right away.
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*/
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if (constraint_ns <= 0)
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return false;
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td->effective_constraint_ns = constraint_ns;
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td->cached_suspend_ok = true;
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}
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/*
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* The children have been suspended already, so we don't need to take
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* their suspend latencies into account here.
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*/
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return td->cached_suspend_ok;
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}
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static bool __default_power_down_ok(struct dev_pm_domain *pd,
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unsigned int state)
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{
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struct generic_pm_domain *genpd = pd_to_genpd(pd);
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struct gpd_link *link;
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struct pm_domain_data *pdd;
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s64 min_off_time_ns;
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s64 off_on_time_ns;
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off_on_time_ns = genpd->states[state].power_off_latency_ns +
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genpd->states[state].power_on_latency_ns;
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min_off_time_ns = -1;
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/*
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* Check if subdomains can be off for enough time.
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*
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* All subdomains have been powered off already at this point.
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*/
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list_for_each_entry(link, &genpd->master_links, master_node) {
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struct generic_pm_domain *sd = link->slave;
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s64 sd_max_off_ns = sd->max_off_time_ns;
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if (sd_max_off_ns < 0)
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continue;
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/*
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* Check if the subdomain is allowed to be off long enough for
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* the current domain to turn off and on (that's how much time
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* it will have to wait worst case).
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*/
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if (sd_max_off_ns <= off_on_time_ns)
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return false;
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if (min_off_time_ns > sd_max_off_ns || min_off_time_ns < 0)
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min_off_time_ns = sd_max_off_ns;
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}
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/*
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* Check if the devices in the domain can be off enough time.
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*/
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list_for_each_entry(pdd, &genpd->dev_list, list_node) {
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struct gpd_timing_data *td;
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s64 constraint_ns;
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/*
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* Check if the device is allowed to be off long enough for the
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* domain to turn off and on (that's how much time it will
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* have to wait worst case).
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*/
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td = &to_gpd_data(pdd)->td;
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constraint_ns = td->effective_constraint_ns;
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/*
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* Zero means "no suspend at all" and this runs only when all
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* devices in the domain are suspended, so it must be positive.
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*/
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if (constraint_ns == PM_QOS_RESUME_LATENCY_NO_CONSTRAINT_NS)
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continue;
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if (constraint_ns <= off_on_time_ns)
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return false;
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if (min_off_time_ns > constraint_ns || min_off_time_ns < 0)
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min_off_time_ns = constraint_ns;
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}
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/*
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* If the computed minimum device off time is negative, there are no
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* latency constraints, so the domain can spend arbitrary time in the
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* "off" state.
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*/
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if (min_off_time_ns < 0)
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return true;
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/*
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* The difference between the computed minimum subdomain or device off
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* time and the time needed to turn the domain on is the maximum
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* theoretical time this domain can spend in the "off" state.
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*/
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genpd->max_off_time_ns = min_off_time_ns -
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genpd->states[state].power_on_latency_ns;
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return true;
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}
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/**
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* default_power_down_ok - Default generic PM domain power off governor routine.
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* @pd: PM domain to check.
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*
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* This routine must be executed under the PM domain's lock.
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*/
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static bool default_power_down_ok(struct dev_pm_domain *pd)
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{
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struct generic_pm_domain *genpd = pd_to_genpd(pd);
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struct gpd_link *link;
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if (!genpd->max_off_time_changed)
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return genpd->cached_power_down_ok;
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/*
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* We have to invalidate the cached results for the masters, so
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* use the observation that default_power_down_ok() is not
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* going to be called for any master until this instance
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* returns.
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*/
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list_for_each_entry(link, &genpd->slave_links, slave_node)
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link->master->max_off_time_changed = true;
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genpd->max_off_time_ns = -1;
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genpd->max_off_time_changed = false;
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genpd->cached_power_down_ok = true;
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genpd->state_idx = genpd->state_count - 1;
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/* Find a state to power down to, starting from the deepest. */
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while (!__default_power_down_ok(pd, genpd->state_idx)) {
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if (genpd->state_idx == 0) {
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genpd->cached_power_down_ok = false;
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break;
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}
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genpd->state_idx--;
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}
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return genpd->cached_power_down_ok;
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}
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static bool always_on_power_down_ok(struct dev_pm_domain *domain)
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{
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return false;
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}
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struct dev_power_governor simple_qos_governor = {
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.suspend_ok = default_suspend_ok,
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.power_down_ok = default_power_down_ok,
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};
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/**
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* pm_genpd_gov_always_on - A governor implementing an always-on policy
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*/
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struct dev_power_governor pm_domain_always_on_gov = {
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.power_down_ok = always_on_power_down_ok,
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.suspend_ok = default_suspend_ok,
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};
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