diff --git a/Documentation/DocBook/media/v4l/common.xml b/Documentation/DocBook/media/v4l/common.xml index b91d25313b63..73c6847436c9 100644 --- a/Documentation/DocBook/media/v4l/common.xml +++ b/Documentation/DocBook/media/v4l/common.xml @@ -564,7 +564,7 @@ automatically. To query and select the standard used by the current video input or output applications call the &VIDIOC-G-STD; and &VIDIOC-S-STD; ioctl, respectively. The received -standard can be sensed with the &VIDIOC-QUERYSTD; ioctl. Note parameter of all these ioctls is a pointer to a &v4l2-std-id; type (a standard set), not an index into the standard enumeration. +standard can be sensed with the &VIDIOC-QUERYSTD; ioctl. Note that the parameter of all these ioctls is a pointer to a &v4l2-std-id; type (a standard set), not an index into the standard enumeration. An alternative to the current scheme is to use pointers to indices as arguments of VIDIOC_G_STD and VIDIOC_S_STD, the &v4l2-input; and @@ -588,30 +588,28 @@ switch to a standard by &v4l2-std-id;. Drivers must implement all video standard ioctls when the device has one or more video inputs or outputs. - Special rules apply to USB cameras where the notion of video -standards makes little sense. More generally any capture device, -output devices accordingly, which is + Special rules apply to devices such as USB cameras where the notion of video +standards makes little sense. More generally for any capture or output device +which is: incapable of capturing fields or frames at the nominal rate of the video standard, or - where timestamps refer -to the instant the field or frame was received by the driver, not the -capture time, or - - - where sequence numbers -refer to the frames received by the driver, not the captured -frames. + that does not support the video standard formats at all. Here the driver shall set the std field of &v4l2-input; and &v4l2-output; -to zero, the VIDIOC_G_STD, +to zero and the VIDIOC_G_STD, VIDIOC_S_STD, VIDIOC_QUERYSTD and VIDIOC_ENUMSTD ioctls shall return the -&EINVAL;. +&ENOTTY;. + See for a rationale. + Applications can make use of the and + flags to determine whether the video standard ioctls +are available for the device. +&ENOTTY;. See for a rationale. Probably even USB cameras follow some well known video standard. It might have been better to explicitly indicate elsewhere if a device cannot live @@ -626,9 +624,9 @@ up to normal expectations, instead of this exception. &v4l2-standard; standard; if (-1 == ioctl (fd, &VIDIOC-G-STD;, &std_id)) { - /* Note when VIDIOC_ENUMSTD always returns EINVAL this + /* Note when VIDIOC_ENUMSTD always returns ENOTTY this is no video device or it falls under the USB exception, - and VIDIOC_G_STD returning EINVAL is no error. */ + and VIDIOC_G_STD returning ENOTTY is no error. */ perror ("VIDIOC_G_STD"); exit (EXIT_FAILURE);