driver core: Add device link flag DL_FLAG_AUTOPROBE_CONSUMER

Add a new device link flag, DL_FLAG_AUTOPROBE_CONSUMER, to request the
driver core to probe for a consumer driver automatically after binding
a driver to the supplier device on a persistent managed device link.

As unbinding the supplier driver on a managed device link causes the
consumer driver to be detached from its device automatically, this
flag provides a complementary mechanism which is needed to address
some "composite device" use cases.
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Documentation/driver-api/device_link.rst

@@ -94,6 +94,15 @@ Similarly, when the device link is added from supplier's ``->probe`` callback,
 ``DL_FLAG_AUTOREMOVE_SUPPLIER`` causes the device link to be automatically
 purged when the supplier fails to probe or later unbinds.
 
+If neither ``DL_FLAG_AUTOREMOVE_CONSUMER`` nor ``DL_FLAG_AUTOREMOVE_SUPPLIER``
+is set, ``DL_FLAG_AUTOPROBE_CONSUMER`` can be used to request the driver core
+to probe for a driver for the consumer driver on the link automatically after
+a driver has been bound to the supplier device.
+
+Note, however, that any combinations of ``DL_FLAG_AUTOREMOVE_CONSUMER``,
+``DL_FLAG_AUTOREMOVE_SUPPLIER`` or ``DL_FLAG_AUTOPROBE_CONSUMER`` with
+``DL_FLAG_STATELESS`` are invalid and cannot be used.
+
 Limitations
 ===========
 

drivers/base/core.c

@@ -208,6 +208,12 @@ static void device_link_rpm_prepare(struct device *consumer,
  * the link will be maintained until one of the devices pointed to by it (either
  * the consumer or the supplier) is unregistered.
  *
+ * Also, if DL_FLAG_STATELESS, DL_FLAG_AUTOREMOVE_CONSUMER and
+ * DL_FLAG_AUTOREMOVE_SUPPLIER are not set in @flags (that is, a persistent
+ * managed device link is being added), the DL_FLAG_AUTOPROBE_CONSUMER flag can
+ * be used to request the driver core to automaticall probe for a consmer
+ * driver after successfully binding a driver to the supplier device.
+ *
  * The combination of DL_FLAG_STATELESS and either DL_FLAG_AUTOREMOVE_CONSUMER
  * or DL_FLAG_AUTOREMOVE_SUPPLIER set in @flags at the same time is invalid and
  * will cause NULL to be returned upfront.
@@ -228,7 +234,12 @@ struct device_link *device_link_add(struct device *consumer,
 
 	if (!consumer || !supplier ||
 	    (flags & DL_FLAG_STATELESS &&
-	     flags & (DL_FLAG_AUTOREMOVE_CONSUMER | DL_FLAG_AUTOREMOVE_SUPPLIER)))
+	     flags & (DL_FLAG_AUTOREMOVE_CONSUMER |
+		      DL_FLAG_AUTOREMOVE_SUPPLIER |
+		      DL_FLAG_AUTOPROBE_CONSUMER)) ||
+	    (flags & DL_FLAG_AUTOPROBE_CONSUMER &&
+	     flags & (DL_FLAG_AUTOREMOVE_CONSUMER |
+		      DL_FLAG_AUTOREMOVE_SUPPLIER)))
 		return NULL;
 
 	if (flags & DL_FLAG_PM_RUNTIME && flags & DL_FLAG_RPM_ACTIVE) {
@@ -589,6 +600,9 @@ void device_links_driver_bound(struct device *dev)
 
 		WARN_ON(link->status != DL_STATE_DORMANT);
 		WRITE_ONCE(link->status, DL_STATE_AVAILABLE);
+
+		if (link->flags & DL_FLAG_AUTOPROBE_CONSUMER)
+			driver_deferred_probe_add(link->consumer);
 	}
 
 	list_for_each_entry(link, &dev->links.suppliers, c_node) {

drivers/base/dd.c

@@ -116,7 +116,7 @@ static void deferred_probe_work_func(struct work_struct *work)
 }
 static DECLARE_WORK(deferred_probe_work, deferred_probe_work_func);
 
-static void driver_deferred_probe_add(struct device *dev)
+void driver_deferred_probe_add(struct device *dev)
 {
 	mutex_lock(&deferred_probe_mutex);
 	if (list_empty(&dev->p->deferred_probe)) {

include/linux/device.h

@@ -341,6 +341,7 @@ struct device *driver_find_device(struct device_driver *drv,
 				  struct device *start, void *data,
 				  int (*match)(struct device *dev, void *data));
 
+void driver_deferred_probe_add(struct device *dev);
 int driver_deferred_probe_check_state(struct device *dev);
 
 /**
@@ -827,12 +828,14 @@ enum device_link_state {
  * PM_RUNTIME: If set, the runtime PM framework will use this link.
  * RPM_ACTIVE: Run pm_runtime_get_sync() on the supplier during link creation.
  * AUTOREMOVE_SUPPLIER: Remove the link automatically on supplier driver unbind.
+ * AUTOPROBE_CONSUMER: Probe consumer driver automatically after supplier binds.
  */
 #define DL_FLAG_STATELESS		BIT(0)
 #define DL_FLAG_AUTOREMOVE_CONSUMER	BIT(1)
 #define DL_FLAG_PM_RUNTIME		BIT(2)
 #define DL_FLAG_RPM_ACTIVE		BIT(3)
 #define DL_FLAG_AUTOREMOVE_SUPPLIER	BIT(4)
+#define DL_FLAG_AUTOPROBE_CONSUMER	BIT(5)
 
 /**
  * struct device_link - Device link representation.