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Commit 0759e80b authored by Rafael J. Wysocki's avatar Rafael J. Wysocki
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PM / QoS: Fix device resume latency framework 

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: 85dc0b8a (PM / QoS: Make it possible to expose PM QoS latency constraints)
Link: https://bugzilla.kernel.org/show_bug.cgi?id=197323


Reported-by: default avatarReinette Chatre <reinette.chatre@intel.com>
Signed-off-by: default avatarRafael J. Wysocki <rafael.j.wysocki@intel.com>
Tested-by: default avatarReinette Chatre <reinette.chatre@intel.com>
Tested-by: default avatarGeert Uytterhoeven <geert+renesas@glider.be>
Tested-by: default avatarTero Kristo <t-kristo@ti.com>
Reviewed-by: default avatarRamesh Thomas <ramesh.thomas@intel.com>
parent 31f18230

Documentation/ABI/testing/sysfs-devices-power

+3 −1
Original line number Diff line number Diff line
@@ -211,7 +211,9 @@ Description: 
		device, after it has been suspended at run time, from a resume

		request to the moment the device will be ready to process I/O,

		in microseconds.  If it is equal to 0, however, this means that

		the PM QoS resume latency may be arbitrary.

		the PM QoS resume latency may be arbitrary and the special value

		"n/a" means that user space cannot accept any resume latency at

		all for the given device.



		Not all drivers support this attribute.  If it isn't supported,

		it is not present.

drivers/base/cpu.c

+2 −1
Original line number Diff line number Diff line
@@ -377,7 +377,8 @@ int register_cpu(struct cpu *cpu, int num) 


	per_cpu(cpu_sys_devices, num) = &cpu->dev;

	register_cpu_under_node(num, cpu_to_node(num));

	dev_pm_qos_expose_latency_limit(&cpu->dev, 0);

	dev_pm_qos_expose_latency_limit(&cpu->dev,

					PM_QOS_RESUME_LATENCY_NO_CONSTRAINT);



	return 0;

}

drivers/base/power/domain.c

+1 −1
Original line number Diff line number Diff line
@@ -1326,7 +1326,7 @@ static struct generic_pm_domain_data *genpd_alloc_dev_data(struct device *dev, 


	gpd_data->base.dev = dev;

	gpd_data->td.constraint_changed = true;

	gpd_data->td.effective_constraint_ns = 0;

	gpd_data->td.effective_constraint_ns = PM_QOS_RESUME_LATENCY_NO_CONSTRAINT_NS;

	gpd_data->nb.notifier_call = genpd_dev_pm_qos_notifier;



	spin_lock_irq(&dev->power.lock);

drivers/base/power/domain_governor.c

+16 −24
Original line number Diff line number Diff line
@@ -33,15 +33,10 @@ static int dev_update_qos_constraint(struct device *dev, void *data) 
		 * known at this point anyway).

		 */

		constraint_ns = dev_pm_qos_read_value(dev);

		if (constraint_ns > 0)

		constraint_ns *= NSEC_PER_USEC;

	}



	/* 0 means "no constraint" */

	if (constraint_ns == 0)

		return 0;



	if (constraint_ns < *constraint_ns_p || *constraint_ns_p == 0)

	if (constraint_ns < *constraint_ns_p)

		*constraint_ns_p = constraint_ns;



	return 0;
@@ -69,12 +64,12 @@ static bool default_suspend_ok(struct device *dev) 
	}

	td->constraint_changed = false;

	td->cached_suspend_ok = false;

	td->effective_constraint_ns = -1;

	td->effective_constraint_ns = 0;

	constraint_ns = __dev_pm_qos_read_value(dev);



	spin_unlock_irqrestore(&dev->power.lock, flags);



	if (constraint_ns < 0)

	if (constraint_ns == 0)

		return false;



	constraint_ns *= NSEC_PER_USEC;
@@ -87,25 +82,25 @@ static bool default_suspend_ok(struct device *dev) 
		device_for_each_child(dev, &constraint_ns,

				      dev_update_qos_constraint);



	if (constraint_ns == 0) {

	if (constraint_ns == PM_QOS_RESUME_LATENCY_NO_CONSTRAINT_NS) {

		/* "No restriction", so the device is allowed to suspend. */

		td->effective_constraint_ns = 0;

		td->effective_constraint_ns = PM_QOS_RESUME_LATENCY_NO_CONSTRAINT_NS;

		td->cached_suspend_ok = true;

	} else if (constraint_ns < 0) {

	} else if (constraint_ns == 0) {

		/*

		 * This triggers if one of the children that don't belong to a

		 * domain has a negative PM QoS constraint and it's better not

		 * to suspend then.  effective_constraint_ns is negative already

		 * and cached_suspend_ok is false, so bail out.

		 * domain has a zero PM QoS constraint and it's better not to

		 * suspend then.  effective_constraint_ns is zero already and

		 * cached_suspend_ok is false, so bail out.

		 */

		return false;

	} else {

		constraint_ns -= td->suspend_latency_ns +

				td->resume_latency_ns;

		/*

		 * effective_constraint_ns is negative already and

		 * cached_suspend_ok is false, so if the computed value is not

		 * positive, return right away.

		 * effective_constraint_ns is zero already and cached_suspend_ok

		 * is false, so if the computed value is not positive, return

		 * right away.

		 */

		if (constraint_ns <= 0)

			return false;
@@ -174,13 +169,10 @@ static bool __default_power_down_ok(struct dev_pm_domain *pd, 
		td = &to_gpd_data(pdd)->td;

		constraint_ns = td->effective_constraint_ns;

		/*

		 * Negative values mean "no suspend at all" and this runs only

		 * when all devices in the domain are suspended, so it must be

		 * 0 at least.

		 *

		 * 0 means "no constraint"

		 * Zero means "no suspend at all" and this runs only when all

		 * devices in the domain are suspended, so it must be positive.

		 */

		if (constraint_ns == 0)

		if (constraint_ns == PM_QOS_RESUME_LATENCY_NO_CONSTRAINT_NS)

			continue;



		if (constraint_ns <= off_on_time_ns)

drivers/base/power/qos.c

+4 −1
Original line number Diff line number Diff line
@@ -139,6 +139,9 @@ static int apply_constraint(struct dev_pm_qos_request *req, 


	switch(req->type) {

	case DEV_PM_QOS_RESUME_LATENCY:

		if (WARN_ON(action != PM_QOS_REMOVE_REQ && value < 0))

			value = 0;



		ret = pm_qos_update_target(&qos->resume_latency,

					   &req->data.pnode, action, value);

		break;
@@ -189,7 +192,7 @@ static int dev_pm_qos_constraints_allocate(struct device *dev) 
	plist_head_init(&c->list);

	c->target_value = PM_QOS_RESUME_LATENCY_DEFAULT_VALUE;

	c->default_value = PM_QOS_RESUME_LATENCY_DEFAULT_VALUE;

	c->no_constraint_value = PM_QOS_RESUME_LATENCY_DEFAULT_VALUE;

	c->no_constraint_value = PM_QOS_RESUME_LATENCY_NO_CONSTRAINT;

	c->type = PM_QOS_MIN;

	c->notifiers = n;