PM / Domains: Add support for genpd on/off notifiers for specific devicescpuidle_psci_to_driver+genpd_onoff_notify

A device may have specific HW constraints that must be obeyed to, before
its corresponding genpd can be powered off - and vice verse for power on.
However, these constraints can't be managed through the regular runtime PM
based deployment for a device, because the access pattern for it, isn't
solely request based.

For these reasons, let's add dev_pm_genpd_add|remove_notifier(), which
should be called with a device that is already being attached to a genpd,
to add/remove a power on/off notifier for it.

Note that, to further clarify when genpd power on/off notifiers should be
used, we can compare with the existing CPU_CLUSTER_PM_ENTER|EXIT notifiers.
In the long run, the genpd power on/off notifiers should be able to replace
these, even if that also requires additional genpd based platform support
for the current users.

Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>

2 files changed, 149 insertions, 4 deletions

diff --git a/drivers/base/power/domain.c b/drivers/base/power/domain.c
index b1634228def2..454729b5cb12 100644
--- a/drivers/base/power/domain.c
+++ b/drivers/base/power/domain.c
@@ -545,13 +545,21 @@ static int genpd_power_off(struct generic_pm_domain *genpd, bool one_dev_on,
 	if (!genpd->gov)
 		genpd->state_idx = 0;
 
+	/* Notify consumers that we are about to power off. */
+	ret = blocking_notifier_call_chain(&genpd->power_notifiers,
+					   GENPD_POWER_OFF, NULL);
+	if (ret)
+		return ret;
+
 	/* Bail out and don't power off, if a subdomain wants power on. */
-	if (atomic_read(&genpd->sd_count) > 0)
-		return -EBUSY;
+	if (atomic_read(&genpd->sd_count) > 0) {
+		ret = -EBUSY;
+		goto busy;
+	}
 
 	ret = _genpd_power_off(genpd, true);
 	if (ret)
-		return ret;
+		goto busy;
 
 	genpd->status = GPD_STATE_POWER_OFF;
 	genpd_update_accounting(genpd);
@@ -564,6 +572,10 @@ static int genpd_power_off(struct generic_pm_domain *genpd, bool one_dev_on,
 	}
 
 	return 0;
+busy:
+	blocking_notifier_call_chain(&genpd->power_notifiers,
+				     GENPD_POWER_ON, NULL);
+	return ret;
 }
 
 /**
@@ -606,6 +618,10 @@ static int genpd_power_on(struct generic_pm_domain *genpd, unsigned int depth)
 	if (ret)
 		goto err;
 
+	/* Inform consumers that we have powered on. */
+	blocking_notifier_call_chain(&genpd->power_notifiers,
+				     GENPD_POWER_ON, NULL);
+
 	genpd->status = GPD_STATE_ACTIVE;
 	genpd_update_accounting(genpd);
 
@@ -948,9 +964,18 @@ static void genpd_sync_power_off(struct generic_pm_domain *genpd, bool use_lock,
 
 	/* Choose the deepest state when suspending */
 	genpd->state_idx = genpd->state_count - 1;
-	if (_genpd_power_off(genpd, false))
+
+	/* Notify consumers that we are about to power off. */
+	if (blocking_notifier_call_chain(&genpd->power_notifiers,
+					 GENPD_POWER_OFF, NULL))
 		return;
 
+	if (_genpd_power_off(genpd, false)) {
+		blocking_notifier_call_chain(&genpd->power_notifiers,
+					     GENPD_POWER_ON, NULL);
+		return;
+	}
+
 	genpd->status = GPD_STATE_POWER_OFF;
 
 	list_for_each_entry(link, &genpd->slave_links, slave_node) {
@@ -998,6 +1023,10 @@ static void genpd_sync_power_on(struct generic_pm_domain *genpd, bool use_lock,
 
 	_genpd_power_on(genpd, false);
 
+	/* Inform consumers that we have powered on. */
+	blocking_notifier_call_chain(&genpd->power_notifiers,
+				     GENPD_POWER_ON, NULL);
+
 	genpd->status = GPD_STATE_ACTIVE;
 }
 
@@ -1593,6 +1622,101 @@ int pm_genpd_remove_device(struct device *dev)
 }
 EXPORT_SYMBOL_GPL(pm_genpd_remove_device);
 
+/**
+ * dev_pm_genpd_add_notifier - Add a genpd power on/off notifier for @dev
+ *
+ * @dev: Device that should be associated with the notifier
+ * @nb: The notifier block to register
+ *
+ * Users may call this function to add a genpd power on/off notifier for an
+ * attached @dev. Only one notifier per device is allowed. The notifier is
+ * sent when genpd is powering on/off the PM domain.
+ *
+ * It is assumed that the user guarantee that the genpd wouldn't be detached
+ * while this routine is getting called.
+ *
+ * Returns 0 on success and negative error values on failures.
+ */
+int dev_pm_genpd_add_notifier(struct device *dev, struct notifier_block *nb)
+{
+	struct generic_pm_domain *genpd;
+	struct generic_pm_domain_data *gpd_data;
+	int ret;
+
+	genpd = dev_to_genpd_safe(dev);
+	if (!genpd)
+		return -ENODEV;
+
+	if (WARN_ON(!dev->power.subsys_data ||
+		     !dev->power.subsys_data->domain_data))
+		return -EINVAL;
+
+	gpd_data = to_gpd_data(dev->power.subsys_data->domain_data);
+	if (gpd_data->power_nb)
+		return -EEXIST;
+
+	genpd_lock(genpd);
+	ret = blocking_notifier_chain_register(&genpd->power_notifiers, nb);
+	genpd_unlock(genpd);
+
+	if (ret) {
+		dev_warn(dev, "failed to add notifier for PM domain %s\n",
+			 genpd->name);
+		return ret;
+	}
+
+	gpd_data->power_nb = nb;
+	return 0;
+}
+EXPORT_SYMBOL_GPL(dev_pm_genpd_add_notifier);
+
+/**
+ * dev_pm_genpd_remove_notifier - Remove a genpd power on/off notifier for @dev
+ *
+ * @dev: Device that is associated with the notifier
+ *
+ * Users may call this function to remove a genpd power on/off notifier for an
+ * attached @dev.
+ *
+ * It is assumed that the user guarantee that the genpd wouldn't be detached
+ * while this routine is getting called.
+ *
+ * Returns 0 on success and negative error values on failures.
+ */
+int dev_pm_genpd_remove_notifier(struct device *dev)
+{
+	struct generic_pm_domain *genpd;
+	struct generic_pm_domain_data *gpd_data;
+	int ret;
+
+	genpd = dev_to_genpd_safe(dev);
+	if (!genpd)
+		return -ENODEV;
+
+	if (WARN_ON(!dev->power.subsys_data ||
+		     !dev->power.subsys_data->domain_data))
+		return -EINVAL;
+
+	gpd_data = to_gpd_data(dev->power.subsys_data->domain_data);
+	if (!gpd_data->power_nb)
+		return -ENODEV;
+
+	genpd_lock(genpd);
+	ret = blocking_notifier_chain_unregister(&genpd->power_notifiers,
+						 gpd_data->power_nb);
+	genpd_unlock(genpd);
+
+	if (ret) {
+		dev_warn(dev, "failed to remove notifier for PM domain %s\n",
+			 genpd->name);
+		return ret;
+	}
+
+	gpd_data->power_nb = NULL;
+	return 0;
+}
+EXPORT_SYMBOL_GPL(dev_pm_genpd_remove_notifier);
+
 static int genpd_add_subdomain(struct generic_pm_domain *genpd,
 			       struct generic_pm_domain *subdomain)
 {
@@ -1763,6 +1887,7 @@ int pm_genpd_init(struct generic_pm_domain *genpd,
 	INIT_LIST_HEAD(&genpd->master_links);
 	INIT_LIST_HEAD(&genpd->slave_links);
 	INIT_LIST_HEAD(&genpd->dev_list);
+	BLOCKING_INIT_NOTIFIER_HEAD(&genpd->power_notifiers);
 	genpd_lock_init(genpd);
 	genpd->gov = gov;
 	INIT_WORK(&genpd->power_off_work, genpd_power_off_work_fn);
diff --git a/include/linux/pm_domain.h b/include/linux/pm_domain.h
index 9ec78ee53652..b4c547a2da97 100644
--- a/include/linux/pm_domain.h
+++ b/include/linux/pm_domain.h
@@ -68,6 +68,11 @@ enum gpd_status {
 	GPD_STATE_POWER_OFF,	/* PM domain is off */
 };
 
+enum genpd_notification_state {
+	GENPD_POWER_ON,
+	GENPD_POWER_OFF
+};
+
 struct dev_power_governor {
 	bool (*power_down_ok)(struct dev_pm_domain *domain);
 	bool (*suspend_ok)(struct device *dev);
@@ -112,6 +117,7 @@ struct generic_pm_domain {
 	cpumask_var_t cpus;		/* A cpumask of the attached CPUs */
 	int (*power_off)(struct generic_pm_domain *domain);
 	int (*power_on)(struct generic_pm_domain *domain);
+	struct blocking_notifier_head power_notifiers; /* Power on/off notifiers */
 	struct opp_table *opp_table;	/* OPP table of the genpd */
 	unsigned int (*opp_to_performance_state)(struct generic_pm_domain *genpd,
 						 struct dev_pm_opp *opp);
@@ -178,6 +184,7 @@ struct generic_pm_domain_data {
 	struct pm_domain_data base;
 	struct gpd_timing_data td;
 	struct notifier_block nb;
+	struct notifier_block *power_nb;
 	int cpu;
 	unsigned int performance_state;
 	void *data;
@@ -204,6 +211,8 @@ int pm_genpd_init(struct generic_pm_domain *genpd,
 		  struct dev_power_governor *gov, bool is_off);
 int pm_genpd_remove(struct generic_pm_domain *genpd);
 int dev_pm_genpd_set_performance_state(struct device *dev, unsigned int state);
+int dev_pm_genpd_add_notifier(struct device *dev, struct notifier_block *nb);
+int dev_pm_genpd_remove_notifier(struct device *dev);
 
 extern struct dev_power_governor simple_qos_governor;
 extern struct dev_power_governor pm_domain_always_on_gov;
@@ -251,6 +260,17 @@ static inline int dev_pm_genpd_set_performance_state(struct device *dev,
 	return -ENOTSUPP;
 }
 
+static inline int dev_pm_genpd_add_notifier(struct device *dev,
+					    struct notifier_block *nb)
+{
+	return -ENOTSUPP;
+}
+
+static inline int dev_pm_genpd_remove_notifier(struct device *dev)
+{
+	return -ENOTSUPP;
+}
+
 #define simple_qos_governor		(*(struct dev_power_governor *)(NULL))
 #define pm_domain_always_on_gov		(*(struct dev_power_governor *)(NULL))
 #endif