PM: wakeup: Add out-of-band system wakeup support for devices

Some devices can wake up the system from suspend even when their power
domains are turned off. This is possible because their system-wakeup logic
resides in an always-on power domain - indicating that they support
out-of-band system wakeup.

Currently, PM domain core doesn't power off such devices if they are marked
as system wakeup sources. To better represent devices with out-of-band
wakeup capability, this patch introduces a new flag out_band_wakeup in
'struct dev_pm_info'.

Two helper APIs are added:
- device_set_out_band_wakeup() - to mark a device as having out-of-band
wakeup capability.
- device_out_band_wakeup() - to query the flag.

Allow the PM core and drivers to distinguish between regular and
out-of-band wakeup sources, enable more accurate power management decision.

Signed-off-by: Peng Fan <[e-mail]>
Reviewed-by: Dhruva Gole <[e-mail]>
Signed-off-by: Ulf Hansson <[e-mail]>

drivers/base/power/main.c

···
 	device_lock(dev);
 
 	dev->power.wakeup_path = false;
+	dev->power.out_band_wakeup = false;
 
 	if (dev->power.no_pm_callbacks)
 		goto unlock;

include/linux/pm.h

···
 	bool			smart_suspend:1;	/* Owned by the PM core */
 	bool			must_resume:1;		/* Owned by the PM core */
 	bool			may_skip_resume:1;	/* Set by subsystems */
+	bool			out_band_wakeup:1;
 	bool			strict_midlayer:1;
 #else
 	bool			should_wakeup:1;

include/linux/pm_wakeup.h

···
 	dev->power.wakeup_path = true;
 }
 
+static inline void device_set_out_band_wakeup(struct device *dev)
+{
+	dev->power.out_band_wakeup = true;
+}
+
+static inline bool device_out_band_wakeup(struct device *dev)
+{
+	return dev->power.out_band_wakeup;
+}
+
 /* drivers/base/power/wakeup.c */
 extern struct wakeup_source *wakeup_source_register(struct device *dev,
 						    const char *name);
···
 }
 
 static inline void device_set_wakeup_path(struct device *dev) {}
+
+static inline void device_set_out_band_wakeup(struct device *dev) {}
+
+static inline bool device_out_band_wakeup(struct device *dev)
+{
+	return false;
+}
 
 static inline void __pm_stay_awake(struct wakeup_source *ws) {}