[RFC Add no_suspend attribute V2] Let the driver know if it's in use

[Michael Trimarchi <trimarchi@gandalf.sssup.it>]

Drivers on embedded systems would be smart enough to know that some
of the devices _should_ remain powered up, because they could still
be useful even when the CPU wasn't running.  The only obstacle is
letting the drivers know when their devices actually _are_ in use
and sometimes this is apparent only at the application level.
The patch add the no_suspend attribute and it can be used by the
the drivers to stop power down during suspend.

Signed-off-by: Michael Trimarchi <trimarchi@gandalf.sssup.it>
Cc: "Alan Stern" <stern@rowland.harvard.edu>
Cc: "Rafael J. Wysocki" <rjw@sisk.pl>
Cc: "Pavel Mackek" <pavel@ucw.cz>
Cc: "Len Brown" <lenb@kernel.org>

---
 drivers/base/power/main.c  |   54 +++++++++++++++++++++++++++++++++++++++++++-
 drivers/base/power/power.h |    5 ++++
 include/linux/device.h     |    1 +
 include/linux/pm.h         |    3 ++
 4 files changed, 62 insertions(+), 1 deletions(-)

diff --git a/drivers/base/power/main.c b/drivers/base/power/main.c
index 69b4ddb..baae309 100644
--- a/drivers/base/power/main.c
+++ b/drivers/base/power/main.c
@@ -65,6 +65,45 @@ void device_pm_unlock(void)
 }
 
 /**
+ *	device_set_no_suspend_enable - Mark the device as used by userspace
+ *	application
+ */
+void device_set_no_suspend_enable(struct device *dev, bool enable)
+{
+	struct device *next;
+
+	mutex_lock(&dpm_list_mtx);
+
+	/* the new status is equal the old one */
+	if (dev->power.no_suspend == !!enable)
+		goto out;
+
+	/* change the device status */
+	dev->power.no_suspend = !!enable;
+	if (dev->power.no_suspend)
+		dev->power.subtree_no_suspend = 0;
+
+	list_for_each_entry_reverse(next, &dev->power.entry, power.entry) {
+		/* 
+		 * exit if we find a node with the same parent of the start
+		 * device
+		 */
+		if (dev->parent && next->parent == dev->parent)
+			break;
+
+		if (next->parent) {
+			/* Propagate the status */
+			next->power.subtree_no_suspend =
+				device_no_suspend_enable(next->parent);
+		}
+	}
+out:
+	mutex_unlock(&dpm_list_mtx);
+	return;
+}
+EXPORT_SYMBOL_GPL(device_set_no_suspend_enable);
+
+/**
  *	device_pm_add - add a device to the list of active devices
  *	@dev:	Device to be added to the list
  */
@@ -78,6 +117,11 @@ void device_pm_add(struct device *dev)
 		if (dev->parent->power.status >= DPM_SUSPENDING)
 			dev_warn(dev, "parent %s should not be sleeping\n",
 				 dev_name(dev->parent));
+		if (device_no_suspend_enable(dev->parent)) {
+			/* if the parent has suspend disable, propagate it
+			 * to the new child */
+			dev->power.subtree_no_suspend = 1;
+		}
 	} else if (transition_started) {
 		/*
 		 * We refuse to register parentless devices while a PM
@@ -87,7 +131,15 @@ void device_pm_add(struct device *dev)
 		dev_WARN(dev, "Parentless device registered during a PM transaction\n");
 	}
 
-	list_add_tail(&dev->power.entry, &dpm_list);
+	if (dev->parent) {
+		/*
+		 * if the device has a parent insert just before it.
+		 */
+		list_add_tail(&dev->power.entry, &(dev->parent)->power.entry);
+	}
+	else
+		list_add_tail(&dev->power.entry, &dpm_list);
+
 	mutex_unlock(&dpm_list_mtx);
 }
 
diff --git a/drivers/base/power/power.h b/drivers/base/power/power.h
index c7cb4fc..a997b20 100644
--- a/drivers/base/power/power.h
+++ b/drivers/base/power/power.h
@@ -3,6 +3,11 @@ static inline void device_pm_init(struct device *dev)
 	dev->power.status = DPM_ON;
 }
 
+static inline int device_no_suspend_enable(struct device *dev)
+{
+	return dev->power.no_suspend || dev->power.subtree_no_suspend;
+}
+
 #ifdef CONFIG_PM_SLEEP
 
 /*
diff --git a/include/linux/device.h b/include/linux/device.h
index 2918c0e..74ca60d 100644
--- a/include/linux/device.h
+++ b/include/linux/device.h
@@ -496,6 +496,7 @@ extern struct device *device_find_child(struct device *dev, void *data,
 extern int device_rename(struct device *dev, char *new_name);
 extern int device_move(struct device *dev, struct device *new_parent,
 		       enum dpm_order dpm_order);
+extern void device_set_no_suspend_enable(struct device *dev, bool enable);
 
 /*
  * Root device objects for grouping under /sys/devices
diff --git a/include/linux/pm.h b/include/linux/pm.h
index 1d4e2d2..e664d63 100644
--- a/include/linux/pm.h
+++ b/include/linux/pm.h
@@ -319,6 +319,9 @@ struct dev_pm_info {
 	pm_message_t		power_state;
 	unsigned		can_wakeup:1;
 	unsigned		should_wakeup:1;
+	unsigned		no_suspend:1;
+	unsigned		subtree_no_suspend:1;
+
 	enum dpm_state		status;		/* Owned by the PM core */
 #ifdef	CONFIG_PM_SLEEP
 	struct list_head	entry;
-- 
1.5.6.5