media: add 'index' to struct media_v2_pad

The v2 pad structure never exposed the pad index, which made it impossible
to call the MEDIA_IOC_SETUP_LINK ioctl, which needs that information.

It is really trivial to just expose this information, so implement this.
Signed-off-by: Hans Verkuil <hansverk@cisco.com>
Acked-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>

drivers/media/media-device.c

@@ -331,6 +331,7 @@ static long media_device_get_topology(struct media_device *mdev, void *arg)
 		kpad.id = pad->graph_obj.id;
 		kpad.entity_id = pad->entity->graph_obj.id;
 		kpad.flags = pad->flags;
+		kpad.index = pad->index;
 
 		if (copy_to_user(upad, &kpad, sizeof(kpad)))
 			ret = -EFAULT;

include/uapi/linux/media.h

@@ -305,11 +305,21 @@ struct media_v2_interface {
 	};
 } __attribute__ ((packed));
 
+/*
+ * Appeared in 4.19.0.
+ *
+ * The media_version argument comes from the media_version field in
+ * struct media_device_info.
+ */
+#define MEDIA_V2_PAD_HAS_INDEX(media_version) \
+	((media_version) >= ((4 << 16) | (19 << 8) | 0))
+
 struct media_v2_pad {
 	__u32 id;
 	__u32 entity_id;
 	__u32 flags;
-	__u32 reserved[5];
+	__u32 index;
+	__u32 reserved[4];
 } __attribute__ ((packed));
 
 struct media_v2_link {