Message-Id: <201205282350.40152.rjw@sisk.pl>
Date:	Mon, 28 May 2012 23:50:39 +0200
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Kevin Hilman <khilman@...com>
Cc:	Linux PM list <linux-pm@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>, Len Brown <lenb@...nel.org>,
	Colin Cross <ccross@...roid.com>,
	Magnus Damm <magnus.damm@...il.com>,
	Arjan van de Ven <arjan@...ux.intel.com>,
	Santosh Shilimkar <santosh.shilimkar@...com>
Subject: [Update 3x][PATCH 2/2] PM / Domains: Add preliminary support for cpuidle

On Friday, May 25, 2012, Kevin Hilman wrote:
> "Rafael J. Wysocki" <rjw@...k.pl> writes:
> 
> > On Thursday, May 24, 2012, Kevin Hilman wrote:
> >> Hi Rafael,
> >> 
> >> "Rafael J. Wysocki" <rjw@...k.pl> writes:
> >> 
> >> > From: Rafael J. Wysocki <rjw@...k.pl>
> >> >
> >> > On some systems there are CPU cores located in the same power
> >> > domains as I/O devices.  Then, power can only be removed from the
> >> > domain if all I/O devices in it are not in use and the CPU core
> >> > is idle.  Add preliminary support for that to the generic PM domains
> >> > framework.
> >> >
> >> > First, the platform is expected to provide a cpuidle driver with one
> >> > extra state designated for use with the generic PM domains code.
> >> > This state should be initially disabled and its exit_latency value
> >> > should be set to whatever time is needed to bring up the CPU core
> >> > itself after restoring power to it, not including the domain's
> >> > power on latency.  Its .enter() callback should point to a procedure
> >> > that will remove power from the domain containing the CPU core at
> >> > the end of the CPU power transition.
> >> >
> >> > The remaining characteristics of the extra cpuidle state, referred to
> >> > as the "domain" cpuidle state below, (e.g. power usage, target
> >> > residency) should be populated in accordance with the properties of
> >> > the hardware.
> >> >
> >> > Next, the platform should execute genpd_attach_cpuidle() on the PM
> >> > domain containing the CPU core.  That will cause the generic PM
> >> > domains framework to treat that domain in a special way such that:
> >> >
> >> >  * When all devices in the domain have been suspended and it is about
> >> >    to be turned off, the states of the devices will be saved, but
> >> >    power will not be removed from the domain.  Instead, the "domain"
> >> >    cpuidle state will be enabled so that power can be removed from
> >> >    the domain when the CPU core is idle and the state has been chosen
> >> >    as the target by the cpuidle governor.
> >> >
> >> >  * When the first I/O device in the domain is resumed and
> >> >    __pm_genpd_poweron(() is called for the first time after
> >> >    power has been removed from the domain, the "domain" cpuidle
> >> >    state will be disabled to avoid subsequent surprise power removals
> >> >    via cpuidle.
> >> 
> >> This looks like a good approach.  I like that it keeps a pretty clean
> >> separation between CPUidle and PM domains.
> >> 
> >> My only comment would be that the recalc of the exit_latency should be
> >> described a bit more.  Specifically, I'm not sure why it's adjused at
> >> every genpd poweron.  At first I thought it was just supposed to be
> >> adjusted upon attach, then adjusted back on detatch, but with the recalc
> >> also in every poweron, I'm a little confused.  Care to clarify?
> >
> > The problem is that the PM domains code measures the time it takes to
> > power off a domain and updates its power on latency parameter if the
> > measured time is greater.  This is done for PM QoS to operate on realistic
> > numbers (most of the time at least).
> 
> OK, I see.  Maybe clarifying that in the changelog would help make that
> clearer.

Sure.  I hope the updated changelog below is better.

Thanks,
Rafael


---
From: Rafael J. Wysocki <rjw@...k.pl>
Subject: PM / Domains: Add preliminary support for cpuidle

On some systems there are CPU cores located in the same power
domains as I/O devices.  Then, power can only be removed from the
domain if all I/O devices in it are not in use and the CPU core
is idle.  Add preliminary support for that to the generic PM domains
framework.

First, the platform is expected to provide a cpuidle driver with one
extra state designated for use with the generic PM domains code.
This state should be initially disabled and its exit_latency value
should be set to whatever time is needed to bring up the CPU core
itself after restoring power to it, not including the domain's
power on latency.  Its .enter() callback should point to a procedure
that will remove power from the domain containing the CPU core at
the end of the CPU power transition.

The remaining characteristics of the extra cpuidle state, referred to
as the "domain" cpuidle state below, (e.g. power usage, target
residency) should be populated in accordance with the properties of
the hardware.

Next, the platform should execute genpd_attach_cpuidle() on the PM
domain containing the CPU core.  That will cause the generic PM
domains framework to treat that domain in a special way such that:

 * When all devices in the domain have been suspended and it is about
   to be turned off, the states of the devices will be saved, but
   power will not be removed from the domain.  Instead, the "domain"
   cpuidle state will be enabled so that power can be removed from
   the domain when the CPU core is idle and the state has been chosen
   as the target by the cpuidle governor.

 * When the first I/O device in the domain is resumed and
   __pm_genpd_poweron(() is called for the first time after
   power has been removed from the domain, the "domain" cpuidle
   state will be disabled to avoid subsequent surprise power removals
   via cpuidle.

The effective exit_latency value of the "domain" cpuidle state
depends on the time needed to bring up the CPU core itself after
restoring power to it as well as on the power on latency of the
domain containing the CPU core.  Thus the "domain" cpuidle state's
exit_latency has to be recomputed every time the domain's power on
latency is updated, which may happen every time power is restored
to the domain, if the measured power on latency is greater than
the latency stored in the corresponding generic_pm_domain structure.

Signed-off-by: Rafael J. Wysocki <rjw@...k.pl>
---
 drivers/base/power/domain.c |  117 ++++++++++++++++++++++++++++++++++++++++++++
 include/linux/pm_domain.h   |   17 ++++++
 2 files changed, 134 insertions(+)

Index: linux/include/linux/pm_domain.h
===================================================================
--- linux.orig/include/linux/pm_domain.h
+++ linux/include/linux/pm_domain.h
@@ -15,6 +15,7 @@
 #include <linux/err.h>
 #include <linux/of.h>
 #include <linux/notifier.h>
+#include <linux/cpuidle.h>
 
 enum gpd_status {
 	GPD_STATE_ACTIVE = 0,	/* PM domain is active */
@@ -45,6 +46,11 @@ struct gpd_dev_ops {
 	bool (*active_wakeup)(struct device *dev);
 };
 
+struct gpd_cpu_data {
+	unsigned int saved_exit_latency;
+	struct cpuidle_state *idle_state;
+};
+
 struct generic_pm_domain {
 	struct dev_pm_domain domain;	/* PM domain operations */
 	struct list_head gpd_list_node;	/* Node in the global PM domains list */
@@ -75,6 +81,7 @@ struct generic_pm_domain {
 	bool max_off_time_changed;
 	bool cached_power_down_ok;
 	struct device_node *of_node; /* Node in device tree */
+	struct gpd_cpu_data *cpu_data;
 };
 
 static inline struct generic_pm_domain *pd_to_genpd(struct dev_pm_domain *pd)
@@ -155,6 +162,8 @@ extern int pm_genpd_add_callbacks(struct
 				  struct gpd_dev_ops *ops,
 				  struct gpd_timing_data *td);
 extern int __pm_genpd_remove_callbacks(struct device *dev, bool clear_td);
+extern int genpd_attach_cpuidle(struct generic_pm_domain *genpd, int state);
+extern int genpd_detach_cpuidle(struct generic_pm_domain *genpd);
 extern void pm_genpd_init(struct generic_pm_domain *genpd,
 			  struct dev_power_governor *gov, bool is_off);
 
@@ -211,6 +220,14 @@ static inline int __pm_genpd_remove_call
 {
 	return -ENOSYS;
 }
+static inline int genpd_attach_cpuidle(struct generic_pm_domain *genpd, int st)
+{
+	return -ENOSYS;
+}
+static inline int genpd_detach_cpuidle(struct generic_pm_domain *genpd)
+{
+	return -ENOSYS;
+}
 static inline void pm_genpd_init(struct generic_pm_domain *genpd,
 				 struct dev_power_governor *gov, bool is_off)
 {
Index: linux/drivers/base/power/domain.c
===================================================================
--- linux.orig/drivers/base/power/domain.c
+++ linux/drivers/base/power/domain.c
@@ -139,6 +139,19 @@ static void genpd_set_active(struct gene
 		genpd->status = GPD_STATE_ACTIVE;
 }
 
+static void genpd_recalc_cpu_exit_latency(struct generic_pm_domain *genpd)
+{
+	s64 usecs64;
+
+	if (!genpd->cpu_data)
+		return;
+
+	usecs64 = genpd->power_on_latency_ns;
+	do_div(usecs64, NSEC_PER_USEC);
+	usecs64 += genpd->cpu_data->saved_exit_latency;
+	genpd->cpu_data->idle_state->exit_latency = usecs64;
+}
+
 /**
  * __pm_genpd_poweron - Restore power to a given PM domain and its masters.
  * @genpd: PM domain to power up.
@@ -176,6 +189,13 @@ int __pm_genpd_poweron(struct generic_pm
 		return 0;
 	}
 
+	if (genpd->cpu_data) {
+		cpuidle_pause_and_lock();
+		genpd->cpu_data->idle_state->disable = true;
+		cpuidle_resume_and_unlock();
+		goto out;
+	}
+
 	/*
 	 * The list is guaranteed not to change while the loop below is being
 	 * executed, unless one of the masters' .power_on() callbacks fiddles
@@ -215,6 +235,7 @@ int __pm_genpd_poweron(struct generic_pm
 		if (elapsed_ns > genpd->power_on_latency_ns) {
 			genpd->power_on_latency_ns = elapsed_ns;
 			genpd->max_off_time_changed = true;
+			genpd_recalc_cpu_exit_latency(genpd);
 			if (genpd->name)
 				pr_warning("%s: Power-on latency exceeded, "
 					"new value %lld ns\n", genpd->name,
@@ -222,6 +243,7 @@ int __pm_genpd_poweron(struct generic_pm
 		}
 	}
 
+ out:
 	genpd_set_active(genpd);
 
 	return 0;
@@ -464,6 +486,21 @@ static int pm_genpd_poweroff(struct gene
 		}
 	}
 
+	if (genpd->cpu_data) {
+		/*
+		 * If cpu_data is set, cpuidle should turn the domain off when
+		 * the CPU in it is idle.  In that case we don't decrement the
+		 * subdomain counts of the master domains, so that power is not
+		 * removed from the current domain prematurely as a result of
+		 * cutting off the masters' power.
+		 */
+		genpd->status = GPD_STATE_POWER_OFF;
+		cpuidle_pause_and_lock();
+		genpd->cpu_data->idle_state->disable = false;
+		cpuidle_resume_and_unlock();
+		goto out;
+	}
+
 	if (genpd->power_off) {
 		ktime_t time_start;
 		s64 elapsed_ns;
@@ -1612,6 +1649,86 @@ int __pm_genpd_remove_callbacks(struct d
 }
 EXPORT_SYMBOL_GPL(__pm_genpd_remove_callbacks);
 
+int genpd_attach_cpuidle(struct generic_pm_domain *genpd, int state)
+{
+	struct cpuidle_driver *cpuidle_drv;
+	struct gpd_cpu_data *cpu_data;
+	struct cpuidle_state *idle_state;
+	int ret = 0;
+
+	if (IS_ERR_OR_NULL(genpd) || state < 0)
+		return -EINVAL;
+
+	genpd_acquire_lock(genpd);
+
+	if (genpd->cpu_data) {
+		ret = -EEXIST;
+		goto out;
+	}
+	cpu_data = kzalloc(sizeof(*cpu_data), GFP_KERNEL);
+	if (!cpu_data) {
+		ret = -ENOMEM;
+		goto out;
+	}
+	cpuidle_drv = cpuidle_driver_ref();
+	if (!cpuidle_drv) {
+		ret = -ENODEV;
+		goto out;
+	}
+	if (cpuidle_drv->state_count <= state) {
+		ret = -EINVAL;
+		goto err;
+	}
+	idle_state = &cpuidle_drv->states[state];
+	if (!idle_state->disable) {
+		ret = -EAGAIN;
+		goto err;
+	}
+	cpu_data->idle_state = idle_state;
+	cpu_data->saved_exit_latency = idle_state->exit_latency;
+	genpd->cpu_data = cpu_data;
+	genpd_recalc_cpu_exit_latency(genpd);
+
+ out:
+	genpd_release_lock(genpd);
+	return ret;
+
+ err:
+	cpuidle_driver_unref();
+	goto out;
+}
+
+int genpd_detach_cpuidle(struct generic_pm_domain *genpd)
+{
+	struct gpd_cpu_data *cpu_data;
+	struct cpuidle_state *idle_state;
+	int ret = 0;
+
+	if (IS_ERR_OR_NULL(genpd))
+		return -EINVAL;
+
+	genpd_acquire_lock(genpd);
+
+	cpu_data = genpd->cpu_data;
+	if (!cpu_data) {
+		ret = -ENODEV;
+		goto out;
+	}
+	idle_state = cpu_data->idle_state;
+	if (!idle_state->disable) {
+		ret = -EAGAIN;
+		goto out;
+	}
+	idle_state->exit_latency = cpu_data->saved_exit_latency;
+	cpuidle_driver_unref();
+	genpd->cpu_data = NULL;
+	kfree(cpu_data);
+
+ out:
+	genpd_release_lock(genpd);
+	return ret;
+}
+
 /* Default device callbacks for generic PM domains. */
 
 /**
--
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