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| -rw-r--r-- | Documentation/userspace-api/media/v4l/querycap.rst | 34 |
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diff --git a/Documentation/userspace-api/media/v4l/querycap.rst b/Documentation/userspace-api/media/v4l/querycap.rst new file mode 100644 index 000000000..15a90271a --- /dev/null +++ b/Documentation/userspace-api/media/v4l/querycap.rst @@ -0,0 +1,34 @@ +.. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later + +.. _querycap: + +********************* +Querying Capabilities +********************* + +Because V4L2 covers a wide variety of devices not all aspects of the API +are equally applicable to all types of devices. Furthermore devices of +the same type have different capabilities and this specification permits +the omission of a few complicated and less important parts of the API. + +The :ref:`VIDIOC_QUERYCAP` ioctl is available to +check if the kernel device is compatible with this specification, and to +query the :ref:`functions <devices>` and :ref:`I/O methods <io>` +supported by the device. + +Starting with kernel version 3.1, :ref:`VIDIOC_QUERYCAP` +will return the V4L2 API version used by the driver, with generally +matches the Kernel version. There's no need of using +:ref:`VIDIOC_QUERYCAP` to check if a specific ioctl +is supported, the V4L2 core now returns ``ENOTTY`` if a driver doesn't +provide support for an ioctl. + +Other features can be queried by calling the respective ioctl, for +example :ref:`VIDIOC_ENUMINPUT` to learn about the +number, types and names of video connectors on the device. Although +abstraction is a major objective of this API, the +:ref:`VIDIOC_QUERYCAP` ioctl also allows driver +specific applications to reliably identify the driver. + +All V4L2 drivers must support :ref:`VIDIOC_QUERYCAP`. +Applications should always call this ioctl after opening the device. |