PM: sleep: Use DPM_FLAG_SMART_SUSPEND conditionally

A recent discussion has revealed that using DPM_FLAG_SMART_SUSPEND
unconditionally is generally problematic because it may lead to
situations in which the device's runtime PM information is internally
inconsistent or does not reflect its real state [1].

For this reason, change the handling of DPM_FLAG_SMART_SUSPEND so that
it is only taken into account if it is consistently set by the drivers
of all devices having any PM callbacks throughout dependency graphs in
accordance with the following rules:

 - The "smart suspend" feature is only enabled for devices whose drivers
   ask for it (that is, set DPM_FLAG_SMART_SUSPEND) and for devices
   without PM callbacks unless they have never had runtime PM enabled.

 - The "smart suspend" feature is not enabled for a device if it has not
   been enabled for the device's parent unless the parent does not take
   children into account or it has never had runtime PM enabled.

 - The "smart suspend" feature is not enabled for a device if it has not
   been enabled for one of the device's suppliers taking runtime PM into
   account unless that supplier has never had runtime PM enabled.

Namely, introduce a new device PM flag called smart_suspend that is only
set if the above conditions are met and update all DPM_FLAG_SMART_SUSPEND
users to check power.smart_suspend instead of directly checking the
latter.

At the same time, drop the power.set_active flage introduced recently
in commit 3775fc5 ("PM: sleep: core: Synchronize runtime PM status
of parents and children") because it is now sufficient to check
power.smart_suspend along with the dev_pm_skip_resume() return value
to decide whether or not pm_runtime_set_active() needs to be called
for the device.

Link: https://lore.kernel.org/linux-pm/CAPDyKFroyU3YDSfw_Y6k3giVfajg3NQGwNWeteJWqpW29BojhQ@mail.gmail.com/ [1]
Fixes: 7585946 ("PM: sleep: core: Restrict power.set_active propagation")
Signed-off-by: Rafael J. Wysocki <[email protected]>
Reviewed-by: Ulf Hansson <[email protected]>
Acked-by: Bjorn Helgaas <[email protected]> # drivers/pci
Link: https://patch.msgid.link/[email protected]

Author: rafaeljw

drivers/acpi/device_pm.c

@@ -1161,7 +1161,7 @@ EXPORT_SYMBOL_GPL(acpi_subsys_complete);
  */
 int acpi_subsys_suspend(struct device *dev)
 {
-	if (!dev_pm_test_driver_flags(dev, DPM_FLAG_SMART_SUSPEND) ||
+	if (!dev_pm_smart_suspend(dev) ||
 	    acpi_dev_needs_resume(dev, ACPI_COMPANION(dev)))
 		pm_runtime_resume(dev);
 
@@ -1320,7 +1320,7 @@ EXPORT_SYMBOL_GPL(acpi_subsys_restore_early);
  */
 int acpi_subsys_poweroff(struct device *dev)
 {
-	if (!dev_pm_test_driver_flags(dev, DPM_FLAG_SMART_SUSPEND) ||
+	if (!dev_pm_smart_suspend(dev) ||
 	    acpi_dev_needs_resume(dev, ACPI_COMPANION(dev)))
 		pm_runtime_resume(dev);
 

drivers/base/power/main.c

@@ -656,15 +656,13 @@ static void device_resume_noirq(struct device *dev, pm_message_t state, bool asy
 	 * so change its status accordingly.
 	 *
 	 * Otherwise, the device is going to be resumed, so set its PM-runtime
-	 * status to "active" unless its power.set_active flag is clear, in
+	 * status to "active" unless its power.smart_suspend flag is clear, in
 	 * which case it is not necessary to update its PM-runtime status.
 	 */
-	if (skip_resume) {
+	if (skip_resume)
 		pm_runtime_set_suspended(dev);
-	} else if (dev->power.set_active) {
+	else if (dev_pm_smart_suspend(dev))
 		pm_runtime_set_active(dev);
-		dev->power.set_active = false;
-	}
 
 	if (dev->pm_domain) {
 		info = "noirq power domain ";
@@ -1282,14 +1280,8 @@ static int device_suspend_noirq(struct device *dev, pm_message_t state, bool asy
 	      dev->power.may_skip_resume))
 		dev->power.must_resume = true;
 
-	if (dev->power.must_resume) {
-		if (dev_pm_test_driver_flags(dev, DPM_FLAG_SMART_SUSPEND)) {
-			dev->power.set_active = true;
-			if (dev->parent && !dev->parent->power.ignore_children)
-				dev->parent->power.set_active = true;
-		}
+	if (dev->power.must_resume)
 		dpm_superior_set_must_resume(dev);
-	}
 
 Complete:
 	complete_all(&dev->power.completion);
@@ -1797,6 +1789,49 @@ int dpm_suspend(pm_message_t state)
 	return error;
 }
 
+static void device_prepare_smart_suspend(struct device *dev)
+{
+	struct device_link *link;
+	int idx;
+
+	/*
+	 * 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.
+	 *
+	 * 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);
+
+	if (!dev_pm_smart_suspend(dev))
+		return;
+
+	if (dev->parent && !dev_pm_smart_suspend(dev->parent) &&
+	    !dev->parent->power.ignore_children && !pm_runtime_blocked(dev->parent)) {
+		dev->power.smart_suspend = false;
+		return;
+	}
+
+	idx = device_links_read_lock();
+
+	list_for_each_entry_rcu_locked(link, &dev->links.suppliers, c_node) {
+		if (!(link->flags | DL_FLAG_PM_RUNTIME))
+			continue;
+
+		if (!dev_pm_smart_suspend(link->supplier) &&
+		    !pm_runtime_blocked(link->supplier)) {
+			dev->power.smart_suspend = false;
+			break;
+		}
+	}
+
+	device_links_read_unlock(idx);
+}
+
 /**
  * device_prepare - Prepare a device for system power transition.
  * @dev: Device to handle.
@@ -1858,6 +1893,7 @@ static int device_prepare(struct device *dev, pm_message_t state)
 		pm_runtime_put(dev);
 		return ret;
 	}
+	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
@@ -2033,6 +2069,5 @@ void device_pm_check_callbacks(struct device *dev)
 
 bool dev_pm_skip_suspend(struct device *dev)
 {
-	return dev_pm_test_driver_flags(dev, DPM_FLAG_SMART_SUSPEND) &&
-		pm_runtime_status_suspended(dev);
+	return dev_pm_smart_suspend(dev) && pm_runtime_status_suspended(dev);
 }

drivers/mfd/intel-lpss.c

@@ -480,7 +480,7 @@ EXPORT_SYMBOL_NS_GPL(intel_lpss_remove, "INTEL_LPSS");
 
 static int resume_lpss_device(struct device *dev, void *data)
 {
-	if (!dev_pm_test_driver_flags(dev, DPM_FLAG_SMART_SUSPEND))
+	if (!dev_pm_smart_suspend(dev))
 		pm_runtime_resume(dev);
 
 	return 0;

drivers/pci/pci-driver.c

@@ -812,8 +812,7 @@ static int pci_pm_suspend(struct device *dev)
 	 * suspend callbacks can cope with runtime-suspended devices, it is
 	 * better to resume the device from runtime suspend here.
 	 */
-	if (!dev_pm_test_driver_flags(dev, DPM_FLAG_SMART_SUSPEND) ||
-	    pci_dev_need_resume(pci_dev)) {
+	if (!dev_pm_smart_suspend(dev) || pci_dev_need_resume(pci_dev)) {
 		pm_runtime_resume(dev);
 		pci_dev->state_saved = false;
 	} else {
@@ -1151,8 +1150,7 @@ static int pci_pm_poweroff(struct device *dev)
 	}
 
 	/* The reason to do that is the same as in pci_pm_suspend(). */
-	if (!dev_pm_test_driver_flags(dev, DPM_FLAG_SMART_SUSPEND) ||
-	    pci_dev_need_resume(pci_dev)) {
+	if (!dev_pm_smart_suspend(dev) || pci_dev_need_resume(pci_dev)) {
 		pm_runtime_resume(dev);
 		pci_dev->state_saved = false;
 	} else {

include/linux/device.h

@@ -1025,6 +1025,15 @@ static inline bool dev_pm_test_driver_flags(struct device *dev, u32 flags)
 	return !!(dev->power.driver_flags & flags);
 }
 
+static inline bool dev_pm_smart_suspend(struct device *dev)
+{
+#ifdef CONFIG_PM_SLEEP
+	return dev->power.smart_suspend;
+#else
+	return false;
+#endif
+}
+
 static inline void device_lock(struct device *dev)
 {
 	mutex_lock(&dev->mutex);

include/linux/pm.h

@@ -680,8 +680,8 @@ struct dev_pm_info {
 	bool			syscore:1;
 	bool			no_pm_callbacks:1;	/* Owned by the PM core */
 	bool			async_in_progress:1;	/* Owned by the PM core */
+	bool			smart_suspend:1;	/* Owned by the PM core */
 	bool			must_resume:1;		/* Owned by the PM core */
-	bool			set_active:1;		/* Owned by the PM core */
 	bool			may_skip_resume:1;	/* Set by subsystems */
 #else
 	bool			should_wakeup:1;