OPP: Add dev_pm_opp_{set|put}_genpd_virt_dev() helper

Multiple generic power domains for a consumer device are supported with
the help of virtual devices, which are created for each consumer device
- genpd pair. These are the device structures which are attached to the
power domain and are required by the OPP core to set the performance
state of the genpd.

The helpers added by this commit are required to be called once for each
of these virtual devices. These are required only if multiple domains
are available for a device, otherwise the actual device structure will
be used instead by the OPP core.

The new helpers also support the complex cases where the consumer device
wouldn't always require all the domains. For example, a camera may
require only one power domain during normal operations but two during
high resolution operations. The consumer driver can call
dev_pm_opp_put_genpd_virt_dev(high_resolution_genpd_virt_dev) if it is
currently operating in the normal mode and doesn't have any performance
requirements from the genpd which manages high resolution power
requirements. The consumer driver can later call
dev_pm_opp_set_genpd_virt_dev(high_resolution_genpd_virt_dev) once it
switches back to the high resolution mode.

The new helpers differ from other OPP set/put helpers as the new ones
can be called with OPPs initialized for the table as we may need to call
them on the fly because of the complex case explained above. For this
reason it is possible that the genpd virt_dev structure may be used in
parallel while the new helpers are running and a new mutex is added to
protect against that. We didn't use the existing opp_table->lock mutex
as that is widely used in the OPP core and we will need this lock in the
dev_pm_opp_set_rate() helper while changing OPP and we need to make sure
there is not much contention while doing that as that's the hotpath.

Reviewed-by: Ulf Hansson <ulf.hansson@linaro.org>
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>

drivers/opp/core.c

@@ -823,6 +823,7 @@ static struct opp_table *_allocate_opp_table(struct device *dev, int index)
 		return NULL;
 
 	mutex_init(&opp_table->lock);
+	mutex_init(&opp_table->genpd_virt_dev_lock);
 	INIT_LIST_HEAD(&opp_table->dev_list);
 
 	opp_dev = _add_opp_dev(dev, opp_table);
@@ -920,6 +921,7 @@ static void _opp_table_kref_release(struct kref *kref)
 		_remove_opp_dev(opp_dev, opp_table);
 	}
 
+	mutex_destroy(&opp_table->genpd_virt_dev_lock);
 	mutex_destroy(&opp_table->lock);
 	list_del(&opp_table->node);
 	kfree(opp_table);
@@ -1602,6 +1604,92 @@ void dev_pm_opp_unregister_set_opp_helper(struct opp_table *opp_table)
 }
 EXPORT_SYMBOL_GPL(dev_pm_opp_unregister_set_opp_helper);
 
+/**
+ * dev_pm_opp_set_genpd_virt_dev - Set virtual genpd device for an index
+ * @dev: Consumer device for which the genpd device is getting set.
+ * @virt_dev: virtual genpd device.
+ * @index: index.
+ *
+ * Multiple generic power domains for a device are supported with the help of
+ * virtual genpd devices, which are created for each consumer device - genpd
+ * pair. These are the device structures which are attached to the power domain
+ * and are required by the OPP core to set the performance state of the genpd.
+ *
+ * This helper will normally be called by the consumer driver of the device
+ * "dev", as only that has details of the genpd devices.
+ *
+ * This helper needs to be called once for each of those virtual devices, but
+ * only if multiple domains are available for a device. Otherwise the original
+ * device structure will be used instead by the OPP core.
+ */
+struct opp_table *dev_pm_opp_set_genpd_virt_dev(struct device *dev,
+						struct device *virt_dev,
+						int index)
+{
+	struct opp_table *opp_table;
+
+	opp_table = dev_pm_opp_get_opp_table(dev);
+	if (!opp_table)
+		return ERR_PTR(-ENOMEM);
+
+	mutex_lock(&opp_table->genpd_virt_dev_lock);
+
+	if (unlikely(!opp_table->genpd_virt_devs ||
+		     index >= opp_table->required_opp_count ||
+		     opp_table->genpd_virt_devs[index])) {
+
+		dev_err(dev, "Invalid request to set required device\n");
+		dev_pm_opp_put_opp_table(opp_table);
+		mutex_unlock(&opp_table->genpd_virt_dev_lock);
+
+		return ERR_PTR(-EINVAL);
+	}
+
+	opp_table->genpd_virt_devs[index] = virt_dev;
+	mutex_unlock(&opp_table->genpd_virt_dev_lock);
+
+	return opp_table;
+}
+
+/**
+ * dev_pm_opp_put_genpd_virt_dev() - Releases resources blocked for genpd device.
+ * @opp_table: OPP table returned by dev_pm_opp_set_genpd_virt_dev().
+ * @virt_dev: virtual genpd device.
+ *
+ * This releases the resource previously acquired with a call to
+ * dev_pm_opp_set_genpd_virt_dev(). The consumer driver shall call this helper
+ * if it doesn't want OPP core to update performance state of a power domain
+ * anymore.
+ */
+void dev_pm_opp_put_genpd_virt_dev(struct opp_table *opp_table,
+				   struct device *virt_dev)
+{
+	int i;
+
+	/*
+	 * Acquire genpd_virt_dev_lock to make sure virt_dev isn't getting
+	 * used in parallel.
+	 */
+	mutex_lock(&opp_table->genpd_virt_dev_lock);
+
+	for (i = 0; i < opp_table->required_opp_count; i++) {
+		if (opp_table->genpd_virt_devs[i] != virt_dev)
+			continue;
+
+		opp_table->genpd_virt_devs[i] = NULL;
+		dev_pm_opp_put_opp_table(opp_table);
+
+		/* Drop the vote */
+		dev_pm_genpd_set_performance_state(virt_dev, 0);
+		break;
+	}
+
+	mutex_unlock(&opp_table->genpd_virt_dev_lock);
+
+	if (unlikely(i == opp_table->required_opp_count))
+		dev_err(virt_dev, "Failed to find required device entry\n");
+}
+
 /**
  * dev_pm_opp_add()  - Add an OPP table from a table definitions
  * @dev:	device for which we do this operation

drivers/opp/of.c

@@ -134,6 +134,7 @@ static struct opp_table *_find_table_of_opp_np(struct device_node *opp_np)
 static void _opp_table_free_required_tables(struct opp_table *opp_table)
 {
 	struct opp_table **required_opp_tables = opp_table->required_opp_tables;
+	struct device **genpd_virt_devs = opp_table->genpd_virt_devs;
 	int i;
 
 	if (!required_opp_tables)
@@ -147,8 +148,10 @@ static void _opp_table_free_required_tables(struct opp_table *opp_table)
 	}
 
 	kfree(required_opp_tables);
+	kfree(genpd_virt_devs);
 
 	opp_table->required_opp_count = 0;
+	opp_table->genpd_virt_devs = NULL;
 	opp_table->required_opp_tables = NULL;
 }
 
@@ -161,6 +164,7 @@ static void _opp_table_alloc_required_tables(struct opp_table *opp_table,
 					     struct device_node *opp_np)
 {
 	struct opp_table **required_opp_tables;
+	struct device **genpd_virt_devs = NULL;
 	struct device_node *required_np, *np;
 	int count, i;
 
@@ -175,11 +179,21 @@ static void _opp_table_alloc_required_tables(struct opp_table *opp_table,
 	if (!count)
 		goto put_np;
 
+	if (count > 1) {
+		genpd_virt_devs = kcalloc(count, sizeof(*genpd_virt_devs),
+					GFP_KERNEL);
+		if (!genpd_virt_devs)
+			goto put_np;
+	}
+
 	required_opp_tables = kcalloc(count, sizeof(*required_opp_tables),
 				      GFP_KERNEL);
-	if (!required_opp_tables)
+	if (!required_opp_tables) {
+		kfree(genpd_virt_devs);
 		goto put_np;
+	}
 
+	opp_table->genpd_virt_devs = genpd_virt_devs;
 	opp_table->required_opp_tables = required_opp_tables;
 	opp_table->required_opp_count = count;
 

drivers/opp/opp.h

@@ -135,6 +135,8 @@ enum opp_table_access {
  * @parsed_static_opps: True if OPPs are initialized from DT.
  * @shared_opp: OPP is shared between multiple devices.
  * @suspend_opp: Pointer to OPP to be used during device suspend.
+ * @genpd_virt_dev_lock: Mutex protecting the genpd virtual device pointers.
+ * @genpd_virt_devs: List of virtual devices for multiple genpd support.
  * @required_opp_tables: List of device OPP tables that are required by OPPs in
  *		this table.
  * @required_opp_count: Number of required devices.
@@ -177,6 +179,8 @@ struct opp_table {
 	enum opp_table_access shared_opp;
 	struct dev_pm_opp *suspend_opp;
 
+	struct mutex genpd_virt_dev_lock;
+	struct device **genpd_virt_devs;
 	struct opp_table **required_opp_tables;
 	unsigned int required_opp_count;
 

include/linux/pm_opp.h

@@ -126,6 +126,8 @@ struct opp_table *dev_pm_opp_set_clkname(struct device *dev, const char * name);
 void dev_pm_opp_put_clkname(struct opp_table *opp_table);
 struct opp_table *dev_pm_opp_register_set_opp_helper(struct device *dev, int (*set_opp)(struct dev_pm_set_opp_data *data));
 void dev_pm_opp_unregister_set_opp_helper(struct opp_table *opp_table);
+struct opp_table *dev_pm_opp_set_genpd_virt_dev(struct device *dev, struct device *virt_dev, int index);
+void dev_pm_opp_put_genpd_virt_dev(struct opp_table *opp_table, struct device *virt_dev);
 int dev_pm_opp_set_rate(struct device *dev, unsigned long target_freq);
 int dev_pm_opp_set_sharing_cpus(struct device *cpu_dev, const struct cpumask *cpumask);
 int dev_pm_opp_get_sharing_cpus(struct device *cpu_dev, struct cpumask *cpumask);
@@ -272,6 +274,12 @@ static inline struct opp_table *dev_pm_opp_set_clkname(struct device *dev, const
 
 static inline void dev_pm_opp_put_clkname(struct opp_table *opp_table) {}
 
+static inline struct opp_table *dev_pm_opp_set_genpd_virt_dev(struct device *dev, struct device *virt_dev, int index)
+{
+	return ERR_PTR(-ENOTSUPP);
+}
+
+static inline void dev_pm_opp_put_genpd_virt_dev(struct opp_table *opp_table, struct device *virt_dev) {}
 static inline int dev_pm_opp_set_rate(struct device *dev, unsigned long target_freq)
 {
 	return -ENOTSUPP;