PM / Runtime: Add synchronous runtime interface for interrupt handlers (v3)

This patch (as1431c) makes the synchronous runtime-PM interface
suitable for use in interrupt handlers.  Subsystems can call the new
pm_runtime_irq_safe() function to tell the PM core that a device's
runtime_suspend and runtime_resume callbacks should be invoked with
interrupts disabled and the spinlock held.  This permits the
pm_runtime_get_sync() and the new pm_runtime_put_sync_suspend()
routines to be called from within interrupt handlers.

When a device is declared irq-safe in this way, the PM core increments
the parent's usage count, so the parent will never be runtime
suspended.  This prevents difficult situations in which an irq-safe
device can't resume because it is forced to wait for its non-irq-safe
parent.
Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>

Documentation/power/runtime_pm.txt

@@ -50,6 +50,15 @@ type's callbacks are not defined) of given device.  The bus type, device type
 and device class callbacks are referred to as subsystem-level callbacks in what
 follows.
 
+By default, the callbacks are always invoked in process context with interrupts
+enabled.  However, subsystems can use the pm_runtime_irq_safe() helper function
+to tell the PM core that a device's ->runtime_suspend() and ->runtime_resume()
+callbacks should be invoked in atomic context with interrupts disabled
+(->runtime_idle() is still invoked the default way).  This implies that these
+callback routines must not block or sleep, but it also means that the
+synchronous helper functions listed at the end of Section 4 can be used within
+an interrupt handler or in an atomic context.
+
 The subsystem-level suspend callback is _entirely_ _responsible_ for handling
 the suspend of the device as appropriate, which may, but need not include
 executing the device driver's own ->runtime_suspend() callback (from the
@@ -237,6 +246,10 @@ defined in include/linux/pm.h:
       Section 8); it may be modified only by the pm_runtime_no_callbacks()
       helper function
 
+  unsigned int irq_safe;
+    - indicates that the ->runtime_suspend() and ->runtime_resume() callbacks
+      will be invoked with the spinlock held and interrupts disabled
+
   unsigned int use_autosuspend;
     - indicates that the device's driver supports delayed autosuspend (see
       Section 9); it may be modified only by the
@@ -344,6 +357,10 @@ drivers/base/power/runtime.c and include/linux/pm_runtime.h:
     - decrement the device's usage counter; if the result is 0 then run
       pm_runtime_idle(dev) and return its result
 
+  int pm_runtime_put_sync_suspend(struct device *dev);
+    - decrement the device's usage counter; if the result is 0 then run
+      pm_runtime_suspend(dev) and return its result
+
   int pm_runtime_put_sync_autosuspend(struct device *dev);
     - decrement the device's usage counter; if the result is 0 then run
       pm_runtime_autosuspend(dev) and return its result
@@ -397,6 +414,11 @@ drivers/base/power/runtime.c and include/linux/pm_runtime.h:
       PM attributes from /sys/devices/.../power (or prevent them from being
       added when the device is registered)
 
+  void pm_runtime_irq_safe(struct device *dev);
+    - set the power.irq_safe flag for the device, causing the runtime-PM
+      suspend and resume callbacks (but not the idle callback) to be invoked
+      with interrupts disabled
+
   void pm_runtime_mark_last_busy(struct device *dev);
     - set the power.last_busy field to the current time
 
@@ -438,6 +460,15 @@ pm_runtime_suspended()
 pm_runtime_mark_last_busy()
 pm_runtime_autosuspend_expiration()
 
+If pm_runtime_irq_safe() has been called for a device then the following helper
+functions may also be used in interrupt context:
+
+pm_runtime_suspend()
+pm_runtime_autosuspend()
+pm_runtime_resume()
+pm_runtime_get_sync()
+pm_runtime_put_sync_suspend()
+
 5. Run-time PM Initialization, Device Probing and Removal
 
 Initially, the run-time PM is disabled for all devices, which means that the

drivers/base/power/runtime.c

@@ -250,13 +250,16 @@ static int rpm_callback(int (*cb)(struct device *), struct device *dev)
 	if (!cb)
 		return -ENOSYS;
 
+	if (dev->power.irq_safe) {
+		retval = cb(dev);
+	} else {
 		spin_unlock_irq(&dev->power.lock);
 
 		retval = cb(dev);
 
 		spin_lock_irq(&dev->power.lock);
+	}
 	dev->power.runtime_error = retval;
-
 	return retval;
 }
 
@@ -404,7 +407,7 @@ static int rpm_suspend(struct device *dev, int rpmflags)
 		goto out;
 	}
 
-	if (parent && !parent->power.ignore_children) {
+	if (parent && !parent->power.ignore_children && !dev->power.irq_safe) {
 		spin_unlock_irq(&dev->power.lock);
 
 		pm_request_idle(parent);
@@ -527,10 +530,13 @@ static int rpm_resume(struct device *dev, int rpmflags)
 
 	if (!parent && dev->parent) {
 		/*
-		 * Increment the parent's resume counter and resume it if
-		 * necessary.
+		 * Increment the parent's usage counter and resume it if
+		 * necessary.  Not needed if dev is irq-safe; then the
+		 * parent is permanently resumed.
 		 */
 		parent = dev->parent;
+		if (dev->power.irq_safe)
+			goto skip_parent;
 		spin_unlock(&dev->power.lock);
 
 		pm_runtime_get_noresume(parent);
@@ -553,6 +559,7 @@ static int rpm_resume(struct device *dev, int rpmflags)
 			goto out;
 		goto repeat;
 	}
+ skip_parent:
 
 	if (dev->power.no_callbacks)
 		goto no_callback;	/* Assume success. */
@@ -584,7 +591,7 @@ static int rpm_resume(struct device *dev, int rpmflags)
 		rpm_idle(dev, RPM_ASYNC);
 
  out:
-	if (parent) {
+	if (parent && !dev->power.irq_safe) {
 		spin_unlock_irq(&dev->power.lock);
 
 		pm_runtime_put(parent);
@@ -1065,7 +1072,6 @@ EXPORT_SYMBOL_GPL(pm_runtime_allow);
  * Set the power.no_callbacks flag, which tells the PM core that this
  * device is power-managed through its parent and has no run-time PM
  * callbacks of its own.  The run-time sysfs attributes will be removed.
- *
  */
 void pm_runtime_no_callbacks(struct device *dev)
 {
@@ -1077,6 +1083,27 @@ void pm_runtime_no_callbacks(struct device *dev)
 }
 EXPORT_SYMBOL_GPL(pm_runtime_no_callbacks);
 
+/**
+ * pm_runtime_irq_safe - Leave interrupts disabled during callbacks.
+ * @dev: Device to handle
+ *
+ * Set the power.irq_safe flag, which tells the PM core that the
+ * ->runtime_suspend() and ->runtime_resume() callbacks for this device should
+ * always be invoked with the spinlock held and interrupts disabled.  It also
+ * causes the parent's usage counter to be permanently incremented, preventing
+ * the parent from runtime suspending -- otherwise an irq-safe child might have
+ * to wait for a non-irq-safe parent.
+ */
+void pm_runtime_irq_safe(struct device *dev)
+{
+	if (dev->parent)
+		pm_runtime_get_sync(dev->parent);
+	spin_lock_irq(&dev->power.lock);
+	dev->power.irq_safe = 1;
+	spin_unlock_irq(&dev->power.lock);
+}
+EXPORT_SYMBOL_GPL(pm_runtime_irq_safe);
+
 /**
  * update_autosuspend - Handle a change to a device's autosuspend settings.
  * @dev: Device to handle.
@@ -1199,4 +1226,6 @@ void pm_runtime_remove(struct device *dev)
 	/* Change the status back to 'suspended' to match the initial status. */
 	if (dev->power.runtime_status == RPM_ACTIVE)
 		pm_runtime_set_suspended(dev);
+	if (dev->power.irq_safe && dev->parent)
+		pm_runtime_put_sync(dev->parent);
 }

include/linux/pm.h

@@ -486,6 +486,7 @@ struct dev_pm_info {
 	unsigned int		run_wake:1;
 	unsigned int		runtime_auto:1;
 	unsigned int		no_callbacks:1;
+	unsigned int		irq_safe:1;
 	unsigned int		use_autosuspend:1;
 	unsigned int		timer_autosuspends:1;
 	enum rpm_request	request;

include/linux/pm_runtime.h

@@ -40,6 +40,7 @@ extern int pm_generic_runtime_idle(struct device *dev);
 extern int pm_generic_runtime_suspend(struct device *dev);
 extern int pm_generic_runtime_resume(struct device *dev);
 extern void pm_runtime_no_callbacks(struct device *dev);
+extern void pm_runtime_irq_safe(struct device *dev);
 extern void __pm_runtime_use_autosuspend(struct device *dev, bool use);
 extern void pm_runtime_set_autosuspend_delay(struct device *dev, int delay);
 extern unsigned long pm_runtime_autosuspend_expiration(struct device *dev);
@@ -124,6 +125,7 @@ static inline int pm_generic_runtime_idle(struct device *dev) { return 0; }
 static inline int pm_generic_runtime_suspend(struct device *dev) { return 0; }
 static inline int pm_generic_runtime_resume(struct device *dev) { return 0; }
 static inline void pm_runtime_no_callbacks(struct device *dev) {}
+static inline void pm_runtime_irq_safe(struct device *dev) {}
 
 static inline void pm_runtime_mark_last_busy(struct device *dev) {}
 static inline void __pm_runtime_use_autosuspend(struct device *dev,
@@ -196,6 +198,11 @@ static inline int pm_runtime_put_sync(struct device *dev)
 	return __pm_runtime_idle(dev, RPM_GET_PUT);
 }
 
+static inline int pm_runtime_put_sync_suspend(struct device *dev)
+{
+	return __pm_runtime_suspend(dev, RPM_GET_PUT);
+}
+
 static inline int pm_runtime_put_sync_autosuspend(struct device *dev)
 {
 	return __pm_runtime_suspend(dev, RPM_GET_PUT | RPM_AUTO);