[media] v4l2-framework.txt: document new v4l2_device release() callback

Signed-off-by: Hans Verkuil <hverkuil@xs4all.nl> Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>

[media] v4l2-framework.txt: document new v4l2_device release() callback
Signed-off-by: Hans Verkuil <hverkuil@xs4all.nl> Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>
Hans Verkuil · Mauro Carvalho Chehab
1 parent bedf8bcf6b
Showing 1 changed file with 15 additions and 0 deletions Side-by-side Diff
Documentation/video4linux/v4l2-framework.txt
@@ -181,6 +181,21 @@
 	state->instance = atomic_inc_return(&drv_instance) - 1;
 }
  
+If you have multiple device nodes then it can be difficult to know when it is
+safe to unregister v4l2_device. For this purpose v4l2_device has refcounting
+support. The refcount is increased whenever video_register_device is called and
+it is decreased whenever that device node is released. When the refcount reaches
+zero, then the v4l2_device release() callback is called. You can do your final
+cleanup there.
+
+If other device nodes (e.g. ALSA) are created, then you can increase and
+decrease the refcount manually as well by calling:
+
+void v4l2_device_get(struct v4l2_device *v4l2_dev);
+
+or:
+
+int v4l2_device_put(struct v4l2_device *v4l2_dev);
  
 struct v4l2_subdev
 ------------------
...	...	@@ -181,6 +181,21 @@
181	181	state->instance = atomic_inc_return(&drv_instance) - 1;
182	182	}
183	183
	184	+If you have multiple device nodes then it can be difficult to know when it is
	185	+safe to unregister v4l2_device. For this purpose v4l2_device has refcounting
	186	+support. The refcount is increased whenever video_register_device is called and
	187	+it is decreased whenever that device node is released. When the refcount reaches
	188	+zero, then the v4l2_device release() callback is called. You can do your final
	189	+cleanup there.
	190	+
	191	+If other device nodes (e.g. ALSA) are created, then you can increase and
	192	+decrease the refcount manually as well by calling:
	193	+
	194	+void v4l2_device_get(struct v4l2_device *v4l2_dev);
	195	+
	196	+or:
	197	+
	198	+int v4l2_device_put(struct v4l2_device *v4l2_dev);
184	199
185	200	struct v4l2_subdev
186	201	------------------