[PATCH] PM / core: Fix supplier device runtime PM usage counter imbalance

[Rafael J. Wysocki]

From: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>

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 should
pass DL_FLAG_RPM_ACTIVE in flags to it anyway.

Fixes: 21d5c57b3726 (PM / runtime: Use device links)
Reported-by: Ulf Hansson <ulf.hansson@xxxxxxxxxx>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>
---

This is a replacement for commit 1e8378619841 (PM / runtime: Fixup
reference counting of device link suppliers at probe) that is going
to be reverted.

---
 drivers/base/core.c |   15 +++++++--------
 1 file changed, 7 insertions(+), 8 deletions(-)

Index: linux-pm/drivers/base/core.c
===================================================================
--- linux-pm.orig/drivers/base/core.c
+++ linux-pm/drivers/base/core.c
@@ -216,6 +216,13 @@ struct device_link *device_link_add(stru
 			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;
@@ -234,14 +241,6 @@ struct device_link *device_link_add(stru
 		case DL_DEV_DRIVER_BOUND:
 			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().
-				 */
-				if (flags & DL_FLAG_PM_RUNTIME)
-					pm_runtime_get_sync(supplier);
-
 				link->status = DL_STATE_CONSUMER_PROBE;
 				break;
 			case DL_DEV_DRIVER_BOUND: