From 76cb841cb886eef6b3bee341a2266c76578724ad Mon Sep 17 00:00:00 2001 From: Daniel Baumann Date: Mon, 6 May 2024 03:02:30 +0200 Subject: Adding upstream version 4.19.249. Signed-off-by: Daniel Baumann --- Documentation/media/uapi/v4l/querycap.rst | 34 +++++++++++++++++++++++++++++++ 1 file changed, 34 insertions(+) create mode 100644 Documentation/media/uapi/v4l/querycap.rst (limited to 'Documentation/media/uapi/v4l/querycap.rst') diff --git a/Documentation/media/uapi/v4l/querycap.rst b/Documentation/media/uapi/v4l/querycap.rst new file mode 100644 index 000000000..c19cce7a8 --- /dev/null +++ b/Documentation/media/uapi/v4l/querycap.rst @@ -0,0 +1,34 @@ +.. -*- coding: utf-8; mode: rst -*- + +.. _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 ` and :ref:`I/O methods ` +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. -- cgit v1.2.3