VIDIOC_SUBDEV_G_FMT, VIDIOC_SUBDEV_S_FMT — Get or set the data format on a subdev pad
int ioctl( | int fd, |
| int request, | |
struct v4l2_subdev_format *argp
); |
This is an experimental interface and may change in the future.
These ioctls are used to negotiate the frame format at specific subdev pads in the image pipeline.
To retrieve the current format applications set the
pad field of a struct v4l2_subdev_format to the
desired pad number as reported by the media API and the
which field to
V4L2_SUBDEV_FORMAT_ACTIVE. When they call the
VIDIOC_SUBDEV_G_FMT ioctl with a pointer to this
structure the driver fills the members of the format
field.
To change the current format applications set both the
pad and which fields
and all members of the format field. When they
call the VIDIOC_SUBDEV_S_FMT ioctl with a pointer to this
structure the driver verifies the requested format, adjusts it based on the
hardware capabilities and configures the device. Upon return the
struct v4l2_subdev_format contains the current format as would be returned by a
VIDIOC_SUBDEV_G_FMT call.
Applications can query the device capabilities by setting the
which to
V4L2_SUBDEV_FORMAT_TRY. When set, 'try' formats are not
applied to the device by the driver, but are changed exactly as active
formats and stored in the sub-device file handle. Two applications querying
the same sub-device would thus not interact with each other.
For instance, to try a format at the output pad of a sub-device,
applications would first set the try format at the sub-device input with the
VIDIOC_SUBDEV_S_FMT ioctl. They would then either
retrieve the default format at the output pad with the
VIDIOC_SUBDEV_G_FMT ioctl, or set the desired output
pad format with the VIDIOC_SUBDEV_S_FMT ioctl and check
the returned value.
Try formats do not depend on active formats, but can depend on the current links configuration or sub-device controls value. For instance, a low-pass noise filter might crop pixels at the frame boundaries, modifying its output frame size.
Drivers must not return an error solely because the requested format doesn't match the device capabilities. They must instead modify the format to match what the hardware can provide. The modified format should be as close as possible to the original request.
Table A.106. struct v4l2_subdev_format
| __u32 | pad | Pad number as reported by the media controller API. |
| __u32 | which | Format to modified, from enum v4l2_subdev_format_whence. |
| struct v4l2_mbus_framefmt | format | Definition of an image format, see Table 4.20, “struct v4l2_mbus_framefmt” for details. |
| __u32 | reserved[8] | Reserved for future extensions. Applications and drivers must set the array to zero. |
Table A.107. enum v4l2_subdev_format_whence
| V4L2_SUBDEV_FORMAT_TRY | 0 | Try formats, used for querying device capabilities. |
| V4L2_SUBDEV_FORMAT_ACTIVE | 1 | Active formats, applied to the hardware. |
On success 0 is returned, on error -1 and the errno variable is set appropriately. The generic error codes are described at the Generic Error Codes chapter.
The format can't be changed because the pad is currently busy.
This can be caused, for instance, by an active video stream on the
pad. The ioctl must not be retried without performing another action
to fix the problem first. Only returned by
VIDIOC_SUBDEV_S_FMT
The struct v4l2_subdev_format pad
references a non-existing pad, or the which
field references a non-existing format.
On success 0 is returned, on error -1 and the errno variable is set appropriately. The generic error codes are described at the Generic Error Codes chapter.