PM / core: Fix supplier device runtime PM usage counter imbalance

If a device link is added via device_link_add() by the driver of the
link's consumer device, the supplier's runtime PM usage counter is
going to be dropped by the pm_runtime_put_suppliers() call in
driver_probe_device().  However, in that case it is not incremented
unless the supplier driver is already present and the link is not
stateless.  That leads to a runtime PM usage counter imbalance for
the supplier device in a few cases.

To prevent that from happening, bump up the supplier runtime
PM usage counter in device_link_add() for all links with the
DL_FLAG_PM_RUNTIME flag set that are added at the consumer probe
time.  Use pm_runtime_get_noresume() for that as the callers of
device_link_add() who want the supplier to be resumed by it are
expected to pass DL_FLAG_RPM_ACTIVE in flags to it anyway, but
additionally resume the supplier if the link is added during
consumer driver probe to retain the existing behavior for the
callers depending on it.

Fixes: 21d5c57b3726 (PM / runtime: Use device links)
Reported-by: Ulf Hansson <ulf.hansson@linaro.org>
Reviewed-by: Ulf Hansson <ulf.hansson@linaro.org>
Tested-by: Marek Szyprowski <m.szyprowski@samsung.com>
Cc: 4.10+ <stable@vger.kernel.org> # 4.10+
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

drivers/base/core.c

@@ -236,6 +236,13 @@ struct device_link *device_link_add(struct device *consumer,
 			link->rpm_active = true;
 		}
 		pm_runtime_new_link(consumer);
+		/*
+		 * If the link is being added by the consumer driver at probe
+		 * time, balance the decrementation of the supplier's runtime PM
+		 * usage counter after consumer probe in driver_probe_device().
+		 */
+		if (consumer->links.status == DL_DEV_PROBING)
+			pm_runtime_get_noresume(supplier);
 	}
 	get_device(supplier);
 	link->supplier = supplier;
@@ -255,12 +262,12 @@ struct device_link *device_link_add(struct device *consumer,
 			switch (consumer->links.status) {
 			case DL_DEV_PROBING:
 				/*
-				 * Balance the decrementation of the supplier's
-				 * runtime PM usage counter after consumer probe
-				 * in driver_probe_device().
+				 * Some callers expect the link creation during
+				 * consumer driver probe to resume the supplier
+				 * even without DL_FLAG_RPM_ACTIVE.
 				 */
 				if (flags & DL_FLAG_PM_RUNTIME)
-					pm_runtime_get_sync(supplier);
+					pm_runtime_resume(supplier);
 
 				link->status = DL_STATE_CONSUMER_PROBE;
 				break;