usb: typec: More API for cable handling

Thunderbolt 3, and probable USB4 too, will need to be able
to get details about the cables. Adding typec_cable_get()
function that the alternate mode drivers can use to gain
access to gain access to the cable.
Signed-off-by: Heikki Krogerus <heikki.krogerus@linux.intel.com>
Link: https://lore.kernel.org/r/20191230142611.24921-4-heikki.krogerus@linux.intel.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/typec/class.c

@@ -834,6 +834,52 @@ static const struct device_type typec_cable_dev_type = {
 	.release = typec_cable_release,
 };
 
+static int cable_match(struct device *dev, void *data)
+{
+	return is_typec_cable(dev);
+}
+
+/**
+ * typec_cable_get - Get a reference to the USB Type-C cable
+ * @port: The USB Type-C Port the cable is connected to
+ *
+ * The caller must decrement the reference count with typec_cable_put() after
+ * use.
+ */
+struct typec_cable *typec_cable_get(struct typec_port *port)
+{
+	struct device *dev;
+
+	dev = device_find_child(&port->dev, NULL, cable_match);
+	if (!dev)
+		return NULL;
+
+	return to_typec_cable(dev);
+}
+EXPORT_SYMBOL_GPL(typec_cable_get);
+
+/**
+ * typec_cable_get - Decrement the reference count on USB Type-C cable
+ * @cable: The USB Type-C cable
+ */
+void typec_cable_put(struct typec_cable *cable)
+{
+	put_device(&cable->dev);
+}
+EXPORT_SYMBOL_GPL(typec_cable_put);
+
+/**
+ * typec_cable_is_active - Check is the USB Type-C cable active or passive
+ * @cable: The USB Type-C Cable
+ *
+ * Return 1 if the cable is active or 0 if it's passive.
+ */
+int typec_cable_is_active(struct typec_cable *cable)
+{
+	return cable->active;
+}
+EXPORT_SYMBOL_GPL(typec_cable_is_active);
+
 /**
  * typec_cable_set_identity - Report result from Discover Identity command
  * @cable: The cable updated identity values

include/linux/usb/typec.h

@@ -230,6 +230,10 @@ struct typec_cable *typec_register_cable(struct typec_port *port,
 					 struct typec_cable_desc *desc);
 void typec_unregister_cable(struct typec_cable *cable);
 
+struct typec_cable *typec_cable_get(struct typec_port *port);
+void typec_cable_put(struct typec_cable *cable);
+int typec_cable_is_active(struct typec_cable *cable);
+
 struct typec_plug *typec_register_plug(struct typec_cable *cable,
 				       struct typec_plug_desc *desc);
 void typec_unregister_plug(struct typec_plug *plug);