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Due to a historical mishap, the v4l2_subdev_frame_interval structure is the only part of the V4L2 subdev userspace API that doesn't contain a 'which' field. This prevents trying frame intervals using the subdev 'TRY' state mechanism. Adding a 'which' field is simple as the structure has 8 reserved fields. This would however break userspace as the field is currently set to 0, corresponding to V4L2_SUBDEV_FORMAT_TRY, while the corresponding ioctls currently operate on the 'ACTIVE' state. We thus need to add a new subdev client cap, V4L2_SUBDEV_CLIENT_CAP_INTERVAL_USES_WHICH, to indicate that userspace is aware of this new field. All drivers that implement the subdev .get_frame_interval() and .set_frame_interval() operations are updated to return -EINVAL when operating on the TRY state, preserving the current behaviour. While at it, fix a bad copy&paste in the documentation of the struct v4l2_subdev_frame_interval_enum 'which' field. Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com> Reviewed-by: Philipp Zabel <p.zabel@pengutronix.de> # for imx-media Reviewed-by: Hans Verkuil <hverkuil-cisco@xs4all.nl> Reviewed-by: Luca Ceresoli <luca.ceresoli@bootlin.com> # for tegra-video Reviewed-by: Mauro Carvalho Chehab <mchehab@kernel.org> Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
89 lines
3.0 KiB
ReStructuredText
89 lines
3.0 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_CLIENT_CAP:
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************************************************************
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ioctl VIDIOC_SUBDEV_G_CLIENT_CAP, VIDIOC_SUBDEV_S_CLIENT_CAP
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************************************************************
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Name
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====
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VIDIOC_SUBDEV_G_CLIENT_CAP - VIDIOC_SUBDEV_S_CLIENT_CAP - Get or set client
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capabilities.
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Synopsis
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========
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.. c:macro:: VIDIOC_SUBDEV_G_CLIENT_CAP
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``int ioctl(int fd, VIDIOC_SUBDEV_G_CLIENT_CAP, struct v4l2_subdev_client_capability *argp)``
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.. c:macro:: VIDIOC_SUBDEV_S_CLIENT_CAP
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``int ioctl(int fd, VIDIOC_SUBDEV_S_CLIENT_CAP, struct v4l2_subdev_client_capability *argp)``
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Arguments
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=========
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``fd``
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File descriptor returned by :ref:`open() <func-open>`.
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``argp``
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Pointer to struct :c:type:`v4l2_subdev_client_capability`.
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Description
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===========
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These ioctls are used to get and set the client (the application using the
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subdevice ioctls) capabilities. The client capabilities are stored in the file
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handle of the opened subdev device node, and the client must set the
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capabilities for each opened subdev separately.
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By default no client capabilities are set when a subdev device node is opened.
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The purpose of the client capabilities are to inform the kernel of the behavior
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of the client, mainly related to maintaining compatibility with different
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kernel and userspace versions.
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The ``VIDIOC_SUBDEV_G_CLIENT_CAP`` ioctl returns the current client capabilities
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associated with the file handle ``fd``.
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The ``VIDIOC_SUBDEV_S_CLIENT_CAP`` ioctl sets client capabilities for the file
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handle ``fd``. The new capabilities fully replace the current capabilities, the
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ioctl can therefore also be used to remove capabilities that have previously
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been set.
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``VIDIOC_SUBDEV_S_CLIENT_CAP`` modifies the struct
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:c:type:`v4l2_subdev_client_capability` to reflect the capabilities that have
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been accepted. A common case for the kernel not accepting a capability is that
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the kernel is older than the headers the userspace uses, and thus the capability
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is unknown to the kernel.
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.. flat-table:: Client Capabilities
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:header-rows: 1
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* - Capability
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- Description
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* - ``V4L2_SUBDEV_CLIENT_CAP_STREAMS``
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- The client is aware of streams. Setting this flag enables the use
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of 'stream' fields (referring to the stream number) with various
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ioctls. If this is not set (which is the default), the 'stream' fields
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will be forced to 0 by the kernel.
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* - ``V4L2_SUBDEV_CLIENT_CAP_INTERVAL_USES_WHICH``
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- The client is aware of the :c:type:`v4l2_subdev_frame_interval`
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``which`` field. If this is not set (which is the default), the
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``which`` field is forced to ``V4L2_SUBDEV_FORMAT_ACTIVE`` by the
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kernel.
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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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ENOIOCTLCMD
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The kernel does not support this ioctl.
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