PM / runtime: Use device links

Modify the runtime PM framework to use device links to ensure that
supplier devices will not be suspended if any of their consumer
devices are active.

The idea is to reference count suppliers on the consumer's resume
and drop references to them on its suspend.  The information on
whether or not the supplier has been reference counted by the
consumer's (runtime) resume is stored in a new field (rpm_active)
in the link object for each link.

It may be necessary to clean up those references when the
supplier is unbinding and that's why the links whose status is
DEVICE_LINK_SUPPLIER_UNBIND are skipped by the runtime suspend
and resume code.

The above means that if the consumer device is probed in the
runtime-active state, the supplier has to be resumed and reference
counted by device_link_add() so the code works as expected on its
(runtime) suspend.  There is a new flag, DEVICE_LINK_RPM_ACTIVE,
to tell device_link_add() about that (in which case the caller
is responsible for making sure that the consumer really will
be runtime-active when runtime PM is enabled for it).

The other new link flag, DEVICE_LINK_PM_RUNTIME, tells the core
whether or not the link should be used for runtime PM at all.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 26 insertions, 1 deletions

diff --git a/drivers/base/core.c b/drivers/base/core.c
index 3c5ff17f578f..876c62b12462 100644
--- a/drivers/base/core.c
+++ b/drivers/base/core.c
@@ -152,6 +152,14 @@ static int device_reorder_to_tail(struct device *dev, void *not_used)
  * @supplier: Supplier end of the link.
  * @flags: Link flags.
  *
+ * The caller is responsible for the proper synchronization of the link creation
+ * with runtime PM.  First, setting the DL_FLAG_PM_RUNTIME flag will cause the
+ * runtime PM framework to take the link into account.  Second, if the
+ * DL_FLAG_RPM_ACTIVE flag is set in addition to it, the supplier devices will
+ * be forced into the active metastate and reference-counted upon the creation
+ * of the link.  If DL_FLAG_PM_RUNTIME is not set, DL_FLAG_RPM_ACTIVE will be
+ * ignored.
+ *
  * If the DL_FLAG_AUTOREMOVE is set, the link will be removed automatically
  * when the consumer device driver unbinds from it.  The combination of both
  * DL_FLAG_AUTOREMOVE and DL_FLAG_STATELESS set is invalid and will cause NULL
@@ -193,10 +201,19 @@ struct device_link *device_link_add(struct device *consumer,
 		if (link->consumer == consumer)
 			goto out;
 
-	link = kmalloc(sizeof(*link), GFP_KERNEL);
+	link = kzalloc(sizeof(*link), GFP_KERNEL);
 	if (!link)
 		goto out;
 
+	if ((flags & DL_FLAG_PM_RUNTIME) && (flags & DL_FLAG_RPM_ACTIVE)) {
+		if (pm_runtime_get_sync(supplier) < 0) {
+			pm_runtime_put_noidle(supplier);
+			kfree(link);
+			link = NULL;
+			goto out;
+		}
+		link->rpm_active = true;
+	}
 	get_device(supplier);
 	link->supplier = supplier;
 	INIT_LIST_HEAD(&link->s_node);
@@ -213,6 +230,14 @@ struct device_link *device_link_add(struct device *consumer,
 		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: