keys: add lazy scheduling flags and docs

src/pipewire/impl-node.c

@@ -1123,6 +1123,8 @@ static void check_properties(struct pw_impl_node *node)
 			recalc_reason = "driver priority changed";
 		}
 	}
+	node->supports_lazy = pw_properties_get_uint32(node->properties, PW_KEY_NODE_SUPPORTS_LAZY, 0);
+	node->supports_request = pw_properties_get_uint32(node->properties, PW_KEY_NODE_SUPPORTS_REQUEST, 0);
 
 	if ((str = pw_properties_get(node->properties, PW_KEY_NODE_NAME)) &&
 	    (node->name == NULL || !spa_streq(node->name, str))) {

src/pipewire/keys.h

@@ -190,6 +190,15 @@ extern "C" {
 #define PW_KEY_NODE_DRIVER		"node.driver"		/**< node can drive the graph. When the node is
 								  *  selected as the driver, it needs to start
 								  *  the graph periodically. */
+#define PW_KEY_NODE_SUPPORTS_LAZY	"node.supports-lazy"	/**< the node can be a lazy driver. It will listen
+								  *  to RequestProcess commands and take them into
+								  *  account when deciding to start the graph.
+								  *  A value of 0 disables support, a value of > 0
+								  *  enables with increasing preference. */
+#define PW_KEY_NODE_SUPPORTS_REQUEST	"node.supports-request"	/**< The node supports emiting RequestProcess events
+								  *  when it wants the graph to be scheduled.
+								  *  A value of 0 disables support, a value of > 0
+								  *  enables with increasing preference. */
 #define PW_KEY_NODE_DRIVER_ID		"node.driver-id"	/**< the node id of the node assigned as driver
 								  *   for this node */
 #define PW_KEY_NODE_ASYNC		"node.async"		/**< the node wants async scheduling */

src/pipewire/private.h

@@ -752,6 +752,9 @@ struct pw_impl_node {
 
 	char *name;				/** for debug */
 
+	uint32_t supports_lazy;		/**< lazy driver preference */
+	uint32_t supports_request;	/**< request follower preference */
+
 	uint32_t priority_driver;	/** priority for being driver */
 	char **groups;			/** groups to schedule this node in */
 	char **link_groups;		/** groups this node is linked to */