media: mc: Add num_links flag to media_pad

Maintain a counter of the links connected to a pad in the media_pad
structure. This helps checking if a pad is connected to anything, which
will be used in the pipeline building code.

Cc: [e-mail] # 6.1
Signed-off-by: Laurent Pinchart <[e-mail]>
Acked-by: Sakari Ailus <[e-mail]>
Signed-off-by: Hans Verkuil <[e-mail]>

drivers/media/mc/mc-entity.c

···
 
 	/* Remove the reverse links for a data link. */
 	if ((link->flags & MEDIA_LNK_FL_LINK_TYPE) == MEDIA_LNK_FL_DATA_LINK) {
+		link->source->num_links--;
+		link->sink->num_links--;
+
 		if (link->source->entity == entity)
 			remote = link->sink->entity;
 		else
···
 	sink->num_backlinks++;
 	sink->num_links++;
 	source->num_links++;
+
+	link->source->num_links++;
+	link->sink->num_links++;
 
 	return 0;
 }

include/media/media-entity.h

···
  * @graph_obj:	Embedded structure containing the media object common data
  * @entity:	Entity this pad belongs to
  * @index:	Pad index in the entity pads array, numbered from 0 to n
+ * @num_links:	Number of links connected to this pad
  * @sig_type:	Type of the signal inside a media pad
  * @flags:	Pad flags, as defined in
  *		:ref:`include/uapi/linux/media.h <media_header>`
···
 	struct media_gobj graph_obj;	/* must be first field in struct */
 	struct media_entity *entity;
 	u16 index;
+	u16 num_links;
 	enum media_pad_signal_type sig_type;
 	unsigned long flags;