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2b455a551f
Invalid values for the 'which' field of structures passed to multiple
subdev ioctls result in an EINVAL error being returned. The
documentation of the corresponding ioctls indicates this with sentences
such as the following:
the ``which`` field references a non-existing format
This is confusing. Clarify the documentation.
Suggested-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
127 lines
4.5 KiB
ReStructuredText
127 lines
4.5 KiB
ReStructuredText
.. 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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If the subdev device node has been registered in read-only mode, calls to
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``VIDIOC_SUBDEV_S_FRAME_INTERVAL`` are only valid if the ``which`` field is set
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to ``V4L2_SUBDEV_FORMAT_TRY``, otherwise 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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- ``stream``
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- Stream identifier.
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* - __u32
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- ``which``
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- Active or try frame interval, from enum
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:ref:`v4l2_subdev_format_whence <v4l2-subdev-format-whence>`.
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* - __u32
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- ``reserved``\ [7]
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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 :c:type:`v4l2_subdev_frame_interval` ``pad`` references a
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non-existing pad, the ``which`` field has an unsupported value, or the pad
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doesn't support 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 and the ``which`` field is set to ``V4L2_SUBDEV_FORMAT_ACTIVE``.
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