PM: sleep: Suspend async parents after suspending children

In analogy with the previous change affecting the resume path,
make device_suspend() start the async suspend of the device's parent
after the device itself has been processed and make dpm_suspend() start
processing "async" leaf devices (that is, devices without children)
upfront so they don't need to wait for the "sync" devices they don't
depend on.

On the Dell XPS13 9360 in my office, this change reduces the total
duration of device suspend by approximately 100 ms (over 20%).

Suggested-by: Saravana Kannan <saravanak@google.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Link: https://patch.msgid.link/3541233.QJadu78ljV@rjwysocki.net

1 files changed, 63 insertions, 4 deletions

diff --git a/drivers/base/power/main.c b/drivers/base/power/main.c
index aec774c02ffc..7a767c8488dd 100644
--- a/drivers/base/power/main.c
+++ b/drivers/base/power/main.c
@@ -1236,6 +1236,41 @@ EXPORT_SYMBOL_GPL(dpm_resume_end);
 
 /*------------------------- Suspend routines -------------------------*/
 
+static bool dpm_leaf_device(struct device *dev)
+{
+	struct device *child;
+
+	lockdep_assert_held(&dpm_list_mtx);
+
+	child = device_find_any_child(dev);
+	if (child) {
+		put_device(child);
+
+		return false;
+	}
+
+	return true;
+}
+
+static void dpm_async_suspend_parent(struct device *dev, async_func_t func)
+{
+	guard(mutex)(&dpm_list_mtx);
+
+	/*
+	 * If the device is suspended asynchronously and the parent's callback
+	 * deletes both the device and the parent itself, the parent object may
+	 * be freed while this function is running, so avoid that by checking
+	 * if the device has been deleted already as the parent cannot be
+	 * deleted before it.
+	 */
+	if (!device_pm_initialized(dev))
+		return;
+
+	/* Start processing the device's parent if it is "async". */
+	if (dev->parent)
+		dpm_async_with_cleanup(dev->parent, func);
+}
+
 /**
  * resume_event - Return a "resume" message for given "suspend" sleep state.
  * @sleep_state: PM message representing a sleep state.
@@ -1661,6 +1696,8 @@ static void dpm_clear_superiors_direct_complete(struct device *dev)
 	device_links_read_unlock(idx);
 }
 
+static void async_suspend(void *data, async_cookie_t cookie);
+
 /**
  * device_suspend - Execute "suspend" callbacks for given device.
  * @dev: Device to handle.
@@ -1790,7 +1827,13 @@ static int device_suspend(struct device *dev, pm_message_t state, bool async)
 
 	complete_all(&dev->power.completion);
 	TRACE_SUSPEND(error);
-	return error;
+
+	if (error || async_error)
+		return error;
+
+	dpm_async_suspend_parent(dev, async_suspend);
+
+	return 0;
 }
 
 static void async_suspend(void *data, async_cookie_t cookie)
@@ -1808,6 +1851,7 @@ static void async_suspend(void *data, async_cookie_t cookie)
 int dpm_suspend(pm_message_t state)
 {
 	ktime_t starttime = ktime_get();
+	struct device *dev;
 	int error = 0;
 
 	trace_suspend_resume(TPS("dpm_suspend"), state.event, true);
@@ -1821,12 +1865,21 @@ int dpm_suspend(pm_message_t state)
 
 	mutex_lock(&dpm_list_mtx);
 
+	/*
+	 * Start processing "async" leaf devices upfront so they don't need to
+	 * wait for the "sync" devices they don't depend on.
+	 */
+	list_for_each_entry_reverse(dev, &dpm_prepared_list, power.entry) {
+		dpm_clear_async_state(dev);
+		if (dpm_leaf_device(dev))
+			dpm_async_with_cleanup(dev, async_suspend);
+	}
+
 	while (!list_empty(&dpm_prepared_list)) {
-		struct device *dev = to_device(dpm_prepared_list.prev);
+		dev = to_device(dpm_prepared_list.prev);
 
 		list_move(&dev->power.entry, &dpm_suspended_list);
 
-		dpm_clear_async_state(dev);
 		if (dpm_async_fn(dev, async_suspend))
 			continue;
 
@@ -1840,8 +1893,14 @@ int dpm_suspend(pm_message_t state)
 
 		mutex_lock(&dpm_list_mtx);
 
-		if (error || async_error)
+		if (error || async_error) {
+			/*
+			 * Move all devices to the target list to resume them
+			 * properly.
+			 */
+			list_splice(&dpm_prepared_list, &dpm_suspended_list);
 			break;
+		}
 	}
 
 	mutex_unlock(&dpm_list_mtx);