driver core: Allow a device to wait on optional suppliers

Before this change, if a device is waiting on suppliers, it's assumed
that all those suppliers are needed for the device to probe
successfully. This change allows marking a devices as waiting only on
optional suppliers. This allows a device to wait on suppliers (and link
to them as soon as they are available) without preventing the device
from being probed.

Signed-off-by: Saravana Kannan <saravanak@google.com>
Link: https://lore.kernel.org/r/20191028220027.251605-3-saravanak@google.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/base/core.c

@@ -480,13 +480,25 @@ EXPORT_SYMBOL_GPL(device_link_add);
  * This function is NOT meant to be called from the probe function of the
  * consumer but rather from code that creates/adds the consumer device.
  */
-static void device_link_wait_for_supplier(struct device *consumer)
+static void device_link_wait_for_supplier(struct device *consumer,
+					  bool need_for_probe)
 {
 	mutex_lock(&wfs_lock);
 	list_add_tail(&consumer->links.needs_suppliers, &wait_for_suppliers);
+	consumer->links.need_for_probe = need_for_probe;
 	mutex_unlock(&wfs_lock);
 }
 
+static void device_link_wait_for_mandatory_supplier(struct device *consumer)
+{
+	device_link_wait_for_supplier(consumer, true);
+}
+
+static void device_link_wait_for_optional_supplier(struct device *consumer)
+{
+	device_link_wait_for_supplier(consumer, false);
+}
+
 /**
  * device_link_add_missing_supplier_links - Add links from consumer devices to
  *					    supplier devices, leaving any
@@ -656,7 +668,8 @@ int device_links_check_suppliers(struct device *dev)
 	 * probe.
 	 */
 	mutex_lock(&wfs_lock);
-	if (!list_empty(&dev->links.needs_suppliers)) {
+	if (!list_empty(&dev->links.needs_suppliers) &&
+	    dev->links.need_for_probe) {
 		mutex_unlock(&wfs_lock);
 		return -EPROBE_DEFER;
 	}
@@ -760,6 +773,15 @@ void device_links_driver_bound(struct device *dev)
 {
 	struct device_link *link;
 
+	/*
+	 * If a device probes successfully, it's expected to have created all
+	 * the device links it needs to or make new device links as it needs
+	 * them. So, it no longer needs to wait on any suppliers.
+	 */
+	mutex_lock(&wfs_lock);
+	list_del_init(&dev->links.needs_suppliers);
+	mutex_unlock(&wfs_lock);
+
 	device_links_write_lock();
 
 	list_for_each_entry(link, &dev->links.consumers, s_node) {
@@ -2393,7 +2415,7 @@ int device_add(struct device *dev)
 
 	if (fwnode_has_op(dev->fwnode, add_links)
 	    && fwnode_call_int_op(dev->fwnode, add_links, dev))
-		device_link_wait_for_supplier(dev);
+		device_link_wait_for_mandatory_supplier(dev, true);
 
 	bus_probe_device(dev);
 	if (parent)

include/linux/device.h

@@ -1155,13 +1155,16 @@ enum dl_dev_state {
  * @consumers: List of links to consumer devices.
  * @needs_suppliers: Hook to global list of devices waiting for suppliers.
  * @defer_sync: Hook to global list of devices that have deferred sync_state.
+ * @need_for_probe: If needs_suppliers is on a list, this indicates if the
+ *		    suppliers are needed for probe or not.
  * @status: Driver status information.
  */
 struct dev_links_info {
 	struct list_head suppliers;
 	struct list_head consumers;
 	struct list_head needs_suppliers;
 	struct list_head defer_sync;
+	bool need_for_probe;
 	enum dl_dev_state status;
 };