[PATCH v3 1/2] PM / sleep: Add power.direct_complete_default flag

[Tomeu Vizoso <tomeu.vizoso@collabora.com>]

Introduce a new per-device flag power.direct_complete_default that will
instruct the PM core to let that device remain in runtime suspend when
the system goes into a sleep power state, without it having to implement
the prepare() callback.

This is useful because otherwise it would be needed to get dozens of
drivers to implement the prepare() callback even if they don't have a
1-to-1 relationship with a piece of HW.

Signed-off-by: Tomeu Vizoso <tomeu.vizoso@collabora.com>

---

v3:	* Have the flag be a more direct substitute for prepare() as
suggested by Rafael
	* Inherit this flag from the parent device

v2:	* Fix wording as suggested by Kevin Hilman
---
 Documentation/power/runtime_pm.txt | 8 +++++++-
 drivers/base/power/main.c          | 5 +++++
 include/linux/pm.h                 | 1 +
 3 files changed, 13 insertions(+), 1 deletion(-)

diff --git a/Documentation/power/runtime_pm.txt b/Documentation/power/runtime_pm.txt
index e76dc0a..caf7b53 100644
--- a/Documentation/power/runtime_pm.txt
+++ b/Documentation/power/runtime_pm.txt
@@ -228,6 +228,12 @@ defined in include/linux/pm.h:
   unsigned int ignore_children;
     - if set, the value of child_count is ignored (but still updated)
 
+  bool direct_complete_default;
+    - if set, the device will be left runtime-suspended when the system
+      transitions to a sleep state, unless there's a .prepare() callback that
+      returns a non-positive value. This flag is inherited from the parent
+      device when a device is added to the PM core's list of active devices.
+
   unsigned int disable_depth;
     - used for disabling the helper functions (they work normally if this is
       equal to zero); the initial value of it is 1 (i.e. runtime PM is
@@ -669,7 +675,7 @@ system suspend and resume callbacks for all of those devices, except for the
 complete callback, which is then entirely responsible for handling the device
 as appropriate.  This only applies to system suspend transitions that are not
 related to hibernation (see Documentation/power/devices.txt for more
-information).
+information).  See also power.direct_complete_default.
 
 The PM core does its best to reduce the probability of race conditions between
 the runtime PM and system suspend/resume (and hibernation) callbacks by carrying
diff --git a/drivers/base/power/main.c b/drivers/base/power/main.c
index 3d874ec..175ddec 100644
--- a/drivers/base/power/main.c
+++ b/drivers/base/power/main.c
@@ -128,6 +128,9 @@ void device_pm_add(struct device *dev)
 	if (dev->parent && dev->parent->power.is_prepared)
 		dev_warn(dev, "parent %s should not be sleeping\n",
 			dev_name(dev->parent));
+	if (dev->parent)
+		dev->power.direct_complete_default =
+			dev->parent->power.direct_complete_default;
 	list_add_tail(&dev->power.entry, &dpm_list);
 	mutex_unlock(&dpm_list_mtx);
 }
@@ -1589,6 +1592,8 @@ static int device_prepare(struct device *dev, pm_message_t state)
 		trace_device_pm_callback_start(dev, info, state.event);
 		ret = callback(dev);
 		trace_device_pm_callback_end(dev, ret);
+	} else if (dev->power.direct_complete_default) {
+		ret = 1;
 	}
 
 	device_unlock(dev);
diff --git a/include/linux/pm.h b/include/linux/pm.h
index 4890743..fcb3451 100644
--- a/include/linux/pm.h
+++ b/include/linux/pm.h
@@ -565,6 +565,7 @@ struct dev_pm_info {
 	bool			ignore_children:1;
 	bool			early_init:1;	/* Owned by the PM core */
 	bool			direct_complete:1;	/* Owned by the PM core */
+	bool			direct_complete_default:1;	/* Ditto */
 	spinlock_t		lock;
 #ifdef CONFIG_PM_SLEEP
 	struct list_head	entry;
-- 
2.4.1