[PATCH V2 03/12] PM / Domains: Add on-off notifiers

[Rickard Andersson]

Some drivers needs to restore their context directly
when a power domain is activated. For example a driver
handling system bus settings must be able to restore
context before the bus is being used for the first time.
Other examples could be clock settings hardware blocks and
special debugging hardware blocks which should be restored
as early as possible in order to be able to debug direcly
from waking up. Typically these notifers are needed in
systems with CPU coupled power domains. The notifiers
are intended to be trigged by cpuidle driver or the
suspend ops hooks.

The drivers that needs to use these notifiers are
some special cases. Most drivers should not use this
method and instead control their context via the
pm_runtime interface.

Signed-off-by: Rickard Andersson <rickard.andersson at stericsson.com>
---
I believe notifiers are the best solution to the problem of
restoring context early when waking up after sleep. It is
similar to what is done in /kernel/cpu_pm.c but but for a
generic power domain instead.

An alternative solution could be to try to call the drivers
runtime_resume/runtime_suspend callbacks instead via genpd
from cpuidle or suspend/resume. I do not recommend that
solution for the following reasons:

* Altered use of runtime PM. As it is today the driver itself
  controls when to runtime-suspend/runtime-resume.
* Runtime PM is disabled during late stages of suspend.
* Complicates runtime PM for a few special cases.

---
 drivers/base/power/domain.c | 63 +++++++++++++++++++++++++++++++++++++++++++++
 include/linux/pm_domain.h   | 22 ++++++++++++++++
 2 files changed, 85 insertions(+)

diff --git a/drivers/base/power/domain.c b/drivers/base/power/domain.c
index acc3a8d..91e3b7d 100644
--- a/drivers/base/power/domain.c
+++ b/drivers/base/power/domain.c
@@ -1956,6 +1956,68 @@ int pm_genpd_name_detach_cpuidle(const char *name)
 	return pm_genpd_detach_cpuidle(pm_genpd_lookup_name(name));
 }
 
+/**
+ * pm_genpd_register_on_off_notifier - Register to early power on /
+ * late power off notifications.
+ * Only use this function if absolutly needed. It is only intended to be
+ * used for power domains that are coupled with the CPU, that is, power
+ * domains being controlled from cpuidle and the platform suspend ops hooks.
+ * Also only devices that needs their context to be restored directly when
+ * leaving a sleep state should use this method. Most devices should be
+ * fine handling their context and power domains via pm_runtime.
+ * @dev: Device to register.
+ * @nb: Notifier block to be registered.
+ */
+int pm_genpd_register_on_off_notifier(struct device *dev,
+				      struct notifier_block *nb)
+{
+	struct generic_pm_domain *genpd;
+
+	dev_dbg(dev, "%s()\n", __func__);
+
+	genpd = dev_to_genpd(dev);
+
+	return atomic_notifier_chain_register(&genpd->on_off_notifier, nb);
+}
+
+/**
+ * pm_genpd_unregister_on_off_notifier - Unregister to early power on /
+ * late power off notification.
+ * @dev: Device to unregister.
+ * @nb: Notifier block to be unregistered.
+ */
+int pm_genpd_unregister_on_off_notifier(struct device *dev,
+					struct notifier_block *nb)
+{
+	struct generic_pm_domain *genpd;
+
+	dev_dbg(dev, "%s()\n", __func__);
+
+	genpd = dev_to_genpd(dev);
+
+	return atomic_notifier_chain_unregister(&genpd->on_off_notifier, nb);
+}
+
+/**
+ * pm_genpd_notify_power_on_off - Notify that the CPU coupled power
+ * domain is going to be powered off or has been powered on.5D
+ * Intended users of this function are cpuidle drivers and the platform
+ * suspend operations implementation.
+ * @genpd: pm domain that will change state.
+ * @power_on_off: true = has been powered on, false = will power off.
+ */
+int pm_genpd_notify_power_on_off(struct generic_pm_domain *genpd,
+				 bool power_on_off)
+{
+	if (IS_ERR_OR_NULL(genpd))
+		return -EINVAL;
+
+	atomic_notifier_call_chain((&genpd->on_off_notifier),
+				   power_on_off, NULL);
+
+	return 0;
+}
+
 /* Default device callbacks for generic PM domains. */
 
 /**
@@ -2137,6 +2199,7 @@ void pm_genpd_init(struct generic_pm_domain *genpd,
 	atomic_set(&genpd->sd_count, 0);
 	genpd->status = is_off ? GPD_STATE_POWER_OFF : GPD_STATE_ACTIVE;
 	init_waitqueue_head(&genpd->status_wait_queue);
+	ATOMIC_INIT_NOTIFIER_HEAD(&genpd->on_off_notifier);
 	genpd->poweroff_task = NULL;
 	genpd->resume_count = 0;
 	genpd->device_count = 0;
diff --git a/include/linux/pm_domain.h b/include/linux/pm_domain.h
index 7c1d252..bf5e7d514 100644
--- a/include/linux/pm_domain.h
+++ b/include/linux/pm_domain.h
@@ -82,6 +82,7 @@ struct generic_pm_domain {
 	bool cached_power_down_ok;
 	struct device_node *of_node; /* Node in device tree */
 	struct gpd_cpu_data *cpu_data;
+	struct atomic_notifier_head on_off_notifier;
 };
 
 static inline struct generic_pm_domain *pd_to_genpd(struct dev_pm_domain *pd)
@@ -159,6 +160,12 @@ extern int pm_genpd_attach_cpuidle(struct generic_pm_domain *genpd, int state);
 extern int pm_genpd_name_attach_cpuidle(const char *name, int state);
 extern int pm_genpd_detach_cpuidle(struct generic_pm_domain *genpd);
 extern int pm_genpd_name_detach_cpuidle(const char *name);
+extern int pm_genpd_register_on_off_notifier(struct device *dev,
+					     struct notifier_block *nb);
+extern int pm_genpd_unregister_on_off_notifier(struct device *dev,
+					struct notifier_block *nb);
+extern int pm_genpd_notify_power_on_off(struct generic_pm_domain *genpd,
+				  bool power_on_off);
 extern void pm_genpd_init(struct generic_pm_domain *genpd,
 			  struct dev_power_governor *gov, bool is_off);
 
@@ -243,6 +250,21 @@ static inline int pm_genpd_name_detach_cpuidle(const char *name)
 {
 	return -ENOSYS;
 }
+static inline int pm_genpd_register_on_off_notifier(struct device *dev,
+						    struct notifier_block *nb)
+{
+	return -ENOSYS;
+}
+static inline int pm_genpd_unregister_on_off_notifier(struct device *dev,
+						      struct notifier_block *nb)
+{
+	return -ENOSYS;
+}
+static inline int pm_genpd_notify_power_on_off(struct generic_pm_domain *genpd,
+					       bool power_on_off)
+{
+	return -ENOSYS;
+}
 static inline void pm_genpd_init(struct generic_pm_domain *genpd,
 				 struct dev_power_governor *gov, bool is_off)
 {
-- 
1.8.2