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

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Signed-off-by: Hans Verkuil <hverkuil@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>
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Hans Verkuil 2011-02-24 06:28:46 -03:00 committed by Mauro Carvalho Chehab
parent bedf8bcf6b
commit 2335e2b817
1 changed files with 15 additions and 0 deletions
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15
Documentation/video4linux/v4l2-framework.txt
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@ -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
------------------