PM / Runtime: Add no_callbacks flag

Some devices, such as USB interfaces, cannot be power-managed
independently of their parents, i.e., they cannot be put in low power
while the parent remains at full power.  This patch (as1425) creates a
new "no_callbacks" flag, which tells the PM core not to invoke the
runtime-PM callback routines for the such devices but instead to
assume that the callbacks always succeed.  In addition, the
non-debugging runtime-PM sysfs attributes for the devices are removed,
since they are pretty much meaningless.

The advantage of this scheme comes not so much from avoiding the
callbacks themselves, but rather from the fact that without the need
for a process context in which to run the callbacks, more work can be
done in interrupt context.

Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>

1 files changed, 53 insertions, 1 deletions

diff --git a/drivers/base/power/runtime.c b/drivers/base/power/runtime.c
index ed227b7..5bd4daa 100644
--- a/drivers/base/power/runtime.c
+++ b/drivers/base/power/runtime.c
@@ -10,8 +10,10 @@
 #include <linux/sched.h>
 #include <linux/pm_runtime.h>
 #include <linux/jiffies.h>
+#include "power.h"
 
 static int rpm_resume(struct device *dev, int rpmflags);
+static int rpm_suspend(struct device *dev, int rpmflags);
 
 /**
  * update_pm_runtime_accounting - Update the time accounting of power states
@@ -148,6 +150,12 @@ static int rpm_idle(struct device *dev, int rpmflags)
 	/* Pending requests need to be canceled. */
 	dev->power.request = RPM_REQ_NONE;
 
+	if (dev->power.no_callbacks) {
+		/* Assume ->runtime_idle() callback would have suspended. */
+		retval = rpm_suspend(dev, rpmflags);
+		goto out;
+	}
+
 	/* Carry out an asynchronous or a synchronous idle notification. */
 	if (rpmflags & RPM_ASYNC) {
 		dev->power.request = RPM_REQ_IDLE;
@@ -254,6 +262,10 @@ static int rpm_suspend(struct device *dev, int rpmflags)
 		goto repeat;
 	}
 
+	dev->power.deferred_resume = false;
+	if (dev->power.no_callbacks)
+		goto no_callback;	/* Assume success. */
+
 	/* Carry out an asynchronous or a synchronous suspend. */
 	if (rpmflags & RPM_ASYNC) {
 		dev->power.request = RPM_REQ_SUSPEND;
@@ -265,7 +277,6 @@ static int rpm_suspend(struct device *dev, int rpmflags)
 	}
 
 	__update_runtime_status(dev, RPM_SUSPENDING);
-	dev->power.deferred_resume = false;
 
 	if (dev->bus && dev->bus->pm && dev->bus->pm->runtime_suspend) {
 		spin_unlock_irq(&dev->power.lock);
@@ -305,6 +316,7 @@ static int rpm_suspend(struct device *dev, int rpmflags)
 			pm_runtime_cancel_pending(dev);
 		}
 	} else {
+ no_callback:
 		__update_runtime_status(dev, RPM_SUSPENDED);
 		pm_runtime_deactivate_timer(dev);
 
@@ -409,6 +421,23 @@ static int rpm_resume(struct device *dev, int rpmflags)
 		goto repeat;
 	}
 
+	/*
+	 * See if we can skip waking up the parent.  This is safe only if
+	 * power.no_callbacks is set, because otherwise we don't know whether
+	 * the resume will actually succeed.
+	 */
+	if (dev->power.no_callbacks && !parent && dev->parent) {
+		spin_lock(&dev->parent->power.lock);
+		if (dev->parent->power.disable_depth > 0
+		    || dev->parent->power.ignore_children
+		    || dev->parent->power.runtime_status == RPM_ACTIVE) {
+			atomic_inc(&dev->parent->power.child_count);
+			spin_unlock(&dev->parent->power.lock);
+			goto no_callback;	/* Assume success. */
+		}
+		spin_unlock(&dev->parent->power.lock);
+	}
+
 	/* Carry out an asynchronous or a synchronous resume. */
 	if (rpmflags & RPM_ASYNC) {
 		dev->power.request = RPM_REQ_RESUME;
@@ -449,6 +478,9 @@ static int rpm_resume(struct device *dev, int rpmflags)
 		goto repeat;
 	}
 
+	if (dev->power.no_callbacks)
+		goto no_callback;	/* Assume success. */
+
 	__update_runtime_status(dev, RPM_RESUMING);
 
 	if (dev->bus && dev->bus->pm && dev->bus->pm->runtime_resume) {
@@ -482,6 +514,7 @@ static int rpm_resume(struct device *dev, int rpmflags)
 		__update_runtime_status(dev, RPM_SUSPENDED);
 		pm_runtime_cancel_pending(dev);
 	} else {
+ no_callback:
 		__update_runtime_status(dev, RPM_ACTIVE);
 		if (parent)
 			atomic_inc(&parent->power.child_count);
@@ -955,6 +988,25 @@ void pm_runtime_allow(struct device *dev)
 EXPORT_SYMBOL_GPL(pm_runtime_allow);
 
 /**
+ * pm_runtime_no_callbacks - Ignore run-time PM callbacks for a device.
+ * @dev: Device to handle.
+ *
+ * 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)
+{
+	spin_lock_irq(&dev->power.lock);
+	dev->power.no_callbacks = 1;
+	spin_unlock_irq(&dev->power.lock);
+	if (device_is_registered(dev))
+		rpm_sysfs_remove(dev);
+}
+EXPORT_SYMBOL_GPL(pm_runtime_no_callbacks);
+
+/**
  * pm_runtime_init - Initialize run-time PM fields in given device object.
  * @dev: Device object to initialize.
  */