From 2335e2b817186cf79a07311f14560ef8b30f6a9a Mon Sep 17 00:00:00 2001 From: Hans Verkuil Date: Thu, 24 Feb 2011 06:28:46 -0300 Subject: [media] v4l2-framework.txt: document new v4l2_device release() callback Signed-off-by: Hans Verkuil Signed-off-by: Mauro Carvalho Chehab --- Documentation/video4linux/v4l2-framework.txt | 15 +++++++++++++++ 1 file changed, 15 insertions(+) (limited to 'Documentation/video4linux') diff --git a/Documentation/video4linux/v4l2-framework.txt b/Documentation/video4linux/v4l2-framework.txt index 1c8d4492f5c7..7d09114af00b 100644 --- a/Documentation/video4linux/v4l2-framework.txt +++ b/Documentation/video4linux/v4l2-framework.txt @@ -181,6 +181,21 @@ static int __devinit drv_probe(struct pci_dev *pdev, 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 ------------------ -- cgit v1.2.3