PM / Runtime: Respect autosuspend when idle triggers suspend

For devices which don't have a .runtime_idle() callback or if it
returns 0, rpm_idle() will end up in triggering a call to
rpm_suspend(), thus trying to carry out a runtime suspend directly
from runtime_idle().

In the above situation we want to respect devices which has enabled
autosuspend, we therfore append the flag sent to rpm_suspend with
RPM_AUTO.

Do note that drivers still needs to update the device last busy mark,
to control the delay for this circumstance.

Updated runtime PM documentation accordingly.

Signed-off-by: Ulf Hansson <[e-mail]>
Acked-by: Kevin Hilman <[e-mail]>
Acked-by: Alan Stern <[e-mail]>
Signed-off-by: Rafael J. Wysocki <[e-mail]>

Documentation/power/runtime_pm.txt

···
 if the device can be suspended (i.e. if all of the conditions necessary for
 suspending the device are satisfied) and to queue up a suspend request for the
 device in that case.  If there is no idle callback, or if the callback returns
-0, then the PM core will attempt to carry out a runtime suspend of the device;
-in essence, it will call pm_runtime_suspend() directly.  To prevent this (for
-example, if the callback routine has started a delayed suspend), the routine
-should return a non-zero value.  Negative error return codes are ignored by the
-PM core.
+0, then the PM core will attempt to carry out a runtime suspend of the device,
+also respecting devices configured for autosuspend.  In essence this means a
+call to pm_runtime_autosuspend() (do note that drivers needs to update the
+device last busy mark, pm_runtime_mark_last_busy(), to control the delay under
+this circumstance).  To prevent this (for example, if the callback routine has
+started a delayed suspend), the routine must return a non-zero value.  Negative
+error return codes are ignored by the PM core.
 
 The helper functions provided by the PM core, described in Section 4, guarantee
 that the following constraints are met with respect to runtime PM callbacks for
···
     - execute the subsystem-level idle callback for the device; returns an
       error code on failure, where -EINPROGRESS means that ->runtime_idle() is
       already being executed; if there is no callback or the callback returns 0
-      then run pm_runtime_suspend(dev) and return its result
+      then run pm_runtime_autosuspend(dev) and return its result
 
   int pm_runtime_suspend(struct device *dev);
     - execute the subsystem-level suspend callback for the device; returns 0 on

drivers/base/power/runtime.c

···
  * Check if the device's runtime PM status allows it to be suspended.  If
  * another idle notification has been started earlier, return immediately.  If
  * the RPM_ASYNC flag is set then queue an idle-notification request; otherwise
- * run the ->runtime_idle() callback directly.
+ * run the ->runtime_idle() callback directly. If the ->runtime_idle callback
+ * doesn't exist or if it returns 0, call rpm_suspend with the RPM_AUTO flag.
  *
  * This function must be called under dev->power.lock with interrupts disabled.
  */
···
 
  out:
 	trace_rpm_return_int(dev, _THIS_IP_, retval);
-	return retval ? retval : rpm_suspend(dev, rpmflags);
+	return retval ? retval : rpm_suspend(dev, rpmflags | RPM_AUTO);
 }
 
 /**