120 lines
4.1 KiB
ReStructuredText
120 lines
4.1 KiB
ReStructuredText
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.. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later
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.. c:namespace:: V4L
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.. _VIDIOC_SUBDEV_G_FRAME_INTERVAL:
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********************************************************************
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ioctl VIDIOC_SUBDEV_G_FRAME_INTERVAL, VIDIOC_SUBDEV_S_FRAME_INTERVAL
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********************************************************************
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Name
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====
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VIDIOC_SUBDEV_G_FRAME_INTERVAL - VIDIOC_SUBDEV_S_FRAME_INTERVAL - Get or set the frame interval on a subdev pad
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Synopsis
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========
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.. c:macro:: VIDIOC_SUBDEV_G_FRAME_INTERVAL
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``int ioctl(int fd, VIDIOC_SUBDEV_G_FRAME_INTERVAL, struct v4l2_subdev_frame_interval *argp)``
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.. c:macro:: VIDIOC_SUBDEV_S_FRAME_INTERVAL
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``int ioctl(int fd, VIDIOC_SUBDEV_S_FRAME_INTERVAL, struct v4l2_subdev_frame_interval *argp)``
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Arguments
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=========
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``fd``
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File descriptor returned by :c:func:`open()`.
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``argp``
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Pointer to struct :c:type:`v4l2_subdev_frame_interval`.
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Description
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===========
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These ioctls are used to get and set the frame interval at specific
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subdev pads in the image pipeline. The frame interval only makes sense
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for sub-devices that can control the frame period on their own. This
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includes, for instance, image sensors and TV tuners. Sub-devices that
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don't support frame intervals must not implement these ioctls.
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To retrieve the current frame interval applications set the ``pad``
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field of a struct
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:c:type:`v4l2_subdev_frame_interval` to
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the desired pad number as reported by the media controller API. When
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they call the ``VIDIOC_SUBDEV_G_FRAME_INTERVAL`` ioctl with a pointer to
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this structure the driver fills the members of the ``interval`` field.
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To change the current frame interval applications set both the ``pad``
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field and all members of the ``interval`` field. When they call the
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``VIDIOC_SUBDEV_S_FRAME_INTERVAL`` ioctl with a pointer to this
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structure the driver verifies the requested interval, adjusts it based
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on the hardware capabilities and configures the device. Upon return the
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struct
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:c:type:`v4l2_subdev_frame_interval`
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contains the current frame interval as would be returned by a
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``VIDIOC_SUBDEV_G_FRAME_INTERVAL`` call.
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Calling ``VIDIOC_SUBDEV_S_FRAME_INTERVAL`` on a subdev device node that has been
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registered in read-only mode is not allowed. An error is returned and the errno
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variable is set to ``-EPERM``.
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Drivers must not return an error solely because the requested interval
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doesn't match the device capabilities. They must instead modify the
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interval to match what the hardware can provide. The modified interval
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should be as close as possible to the original request.
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Changing the frame interval shall never change the format. Changing the
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format, on the other hand, may change the frame interval.
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Sub-devices that support the frame interval ioctls should implement them
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on a single pad only. Their behaviour when supported on multiple pads of
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the same sub-device is not defined.
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.. c:type:: v4l2_subdev_frame_interval
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.. tabularcolumns:: |p{4.4cm}|p{4.4cm}|p{8.5cm}|
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.. flat-table:: struct v4l2_subdev_frame_interval
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:header-rows: 0
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:stub-columns: 0
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:widths: 1 1 2
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* - __u32
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- ``pad``
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- Pad number as reported by the media controller API.
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* - struct :c:type:`v4l2_fract`
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- ``interval``
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- Period, in seconds, between consecutive video frames.
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* - __u32
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- ``reserved``\ [9]
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- Reserved for future extensions. Applications and drivers must set
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the array to zero.
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Return Value
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============
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On success 0 is returned, on error -1 and the ``errno`` variable is set
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appropriately. The generic error codes are described at the
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:ref:`Generic Error Codes <gen-errors>` chapter.
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EBUSY
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The frame interval can't be changed because the pad is currently
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busy. This can be caused, for instance, by an active video stream on
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the pad. The ioctl must not be retried without performing another
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action to fix the problem first. Only returned by
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``VIDIOC_SUBDEV_S_FRAME_INTERVAL``
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EINVAL
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The struct
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:c:type:`v4l2_subdev_frame_interval`
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``pad`` references a non-existing pad, or the pad doesn't support
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frame intervals.
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EPERM
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The ``VIDIOC_SUBDEV_S_FRAME_INTERVAL`` ioctl has been called on a read-only
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subdevice.
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