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[media] v4l2-framework.txt: document debug attribute

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The debug attribute in /sys/class/video4linux/<devX>/debug was never
documented. Add this.

Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Acked-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>
This commit is contained in:
Hans Verkuil 2014-12-01 10:10:45 -03:00 committed by Mauro Carvalho Chehab
parent 17028cdb74
commit 88f414f476
1 changed files with 23 additions and 2 deletions
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25
Documentation/video4linux/v4l2-framework.txt
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@ -793,8 +793,10 @@ video_register_device_no_warn() instead.
Whenever a device node is created some attributes are also created for you. Whenever a device node is created some attributes are also created for you.
If you look in /sys/class/video4linux you see the devices. Go into e.g. If you look in /sys/class/video4linux you see the devices. Go into e.g.
video0 and you will see 'name' and 'index' attributes. The 'name' attribute video0 and you will see 'name', 'debug' and 'index' attributes. The 'name'
is the 'name' field of the video_device struct. attribute is the 'name' field of the video_device struct. The 'debug' attribute
can be used to enable core debugging. See the next section for more detailed
information on this.
The 'index' attribute is the index of the device node: for each call to The 'index' attribute is the index of the device node: for each call to
video_register_device() the index is just increased by 1. The first video video_register_device() the index is just increased by 1. The first video
@ -816,6 +818,25 @@ video_device was embedded in it. The vdev->release() callback will never
be called if the registration failed, nor should you ever attempt to be called if the registration failed, nor should you ever attempt to
unregister the device if the registration failed. unregister the device if the registration failed.
video device debugging
----------------------
The 'debug' attribute that is created for each video, vbi, radio or swradio
device in /sys/class/video4linux/<devX>/ allows you to enable logging of
file operations.
It is a bitmask and the following bits can be set:
0x01: Log the ioctl name and error code. VIDIOC_(D)QBUF ioctls are only logged
if bit 0x08 is also set.
0x02: Log the ioctl name arguments and error code. VIDIOC_(D)QBUF ioctls are
only logged if bit 0x08 is also set.
0x04: Log the file operations open, release, read, write, mmap and
get_unmapped_area. The read and write operations are only logged if
bit 0x08 is also set.
0x08: Log the read and write file operations and the VIDIOC_QBUF and
VIDIOC_DQBUF ioctls.
0x10: Log the poll file operation.
video_device cleanup video_device cleanup
-------------------- --------------------