PM: sleep: Avoid unnecessary checks in device_prepare_smart_suspend()

JIRA: https://issues.redhat.com/browse/RHEL-80696

commit 520a552
Author: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Date:   Tue Feb 18 21:20:46 2025 +0100

Add an optimization (on top of previous changes) to avoid calling
pm_runtime_blocked(), which involves acquiring the device's PM spinlock,
for devices with no PM callbacks and runtime PM "blocked".

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Reviewed-by: Ulf Hansson <ulf.hansson@linaro.org>
Link: https://patch.msgid.link/2978873.e9J7NaK4W3@rjwysocki.net
Signed-off-by: Mark Langsdorf <mlangsdo@redhat.com>

Author: mlangsdorf

drivers/base/power/main.c

@@ -1796,16 +1796,14 @@ static void device_prepare_smart_suspend(struct device *dev)
 
 	/*
 	 * The "smart suspend" feature is enabled for devices whose drivers ask
-	 * for it and for devices without PM callbacks unless runtime PM is
-	 * disabled and enabling it is blocked for them.
+	 * for it and for devices without PM callbacks.
 	 *
 	 * However, if "smart suspend" is not enabled for the device's parent
 	 * or any of its suppliers that take runtime PM into account, it cannot
 	 * be enabled for the device either.
 	 */
-	dev->power.smart_suspend = (dev->power.no_pm_callbacks ||
-		dev_pm_test_driver_flags(dev, DPM_FLAG_SMART_SUSPEND)) &&
-		!pm_runtime_blocked(dev);
+	dev->power.smart_suspend = dev->power.no_pm_callbacks ||
+		dev_pm_test_driver_flags(dev, DPM_FLAG_SMART_SUSPEND);
 
 	if (!dev_pm_smart_suspend(dev))
 		return;
@@ -1843,6 +1841,7 @@ static void device_prepare_smart_suspend(struct device *dev)
 static int device_prepare(struct device *dev, pm_message_t state)
 {
 	int (*callback)(struct device *) = NULL;
+	bool no_runtime_pm;
 	int ret = 0;
 
 	/*
@@ -1858,7 +1857,7 @@ static int device_prepare(struct device *dev, pm_message_t state)
 	 * suspend-resume cycle is complete, so prepare to trigger a warning on
 	 * subsequent attempts to enable it.
 	 */
-	pm_runtime_block_if_disabled(dev);
+	no_runtime_pm = pm_runtime_block_if_disabled(dev);
 
 	if (dev->power.syscore)
 		return 0;
@@ -1893,7 +1892,10 @@ static int device_prepare(struct device *dev, pm_message_t state)
 		pm_runtime_put(dev);
 		return ret;
 	}
-	device_prepare_smart_suspend(dev);
+	/* Do not enable "smart suspend" for devices without runtime PM. */
+	if (!no_runtime_pm)
+		device_prepare_smart_suspend(dev);
+
 	/*
 	 * A positive return value from ->prepare() means "this device appears
 	 * to be runtime-suspended and its state is fine, so if it really is

drivers/base/power/runtime.c

@@ -1460,14 +1460,19 @@ int pm_runtime_barrier(struct device *dev)
 }
 EXPORT_SYMBOL_GPL(pm_runtime_barrier);
 
-void pm_runtime_block_if_disabled(struct device *dev)
+bool pm_runtime_block_if_disabled(struct device *dev)
 {
+	bool ret;
+
 	spin_lock_irq(&dev->power.lock);
 
-	if (dev->power.disable_depth && dev->power.last_status == RPM_INVALID)
+	ret = dev->power.disable_depth && dev->power.last_status == RPM_INVALID;
+	if (ret)
 		dev->power.last_status = RPM_BLOCKED;
 
 	spin_unlock_irq(&dev->power.lock);
+
+	return ret;
 }
 
 void pm_runtime_unblock(struct device *dev)

include/linux/pm_runtime.h

@@ -77,7 +77,7 @@ extern int pm_runtime_get_if_in_use(struct device *dev);
 extern int pm_schedule_suspend(struct device *dev, unsigned int delay);
 extern int __pm_runtime_set_status(struct device *dev, unsigned int status);
 extern int pm_runtime_barrier(struct device *dev);
-extern void pm_runtime_block_if_disabled(struct device *dev);
+extern bool pm_runtime_block_if_disabled(struct device *dev);
 extern void pm_runtime_unblock(struct device *dev);
 extern void pm_runtime_enable(struct device *dev);
 extern void __pm_runtime_disable(struct device *dev, bool check_resume);
@@ -274,7 +274,7 @@ static inline int pm_runtime_get_if_active(struct device *dev)
 static inline int __pm_runtime_set_status(struct device *dev,
 					    unsigned int status) { return 0; }
 static inline int pm_runtime_barrier(struct device *dev) { return 0; }
-static inline void pm_runtime_block_if_disabled(struct device *dev) {}
+static inline bool pm_runtime_block_if_disabled(struct device *dev) { return true; }
 static inline void pm_runtime_unblock(struct device *dev) {}
 static inline void pm_runtime_enable(struct device *dev) {}
 static inline void __pm_runtime_disable(struct device *dev, bool c) {}