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author | Mauro Carvalho Chehab <mchehab+huawei@kernel.org> | 2020-03-04 12:21:39 +0300 |
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committer | Mauro Carvalho Chehab <mchehab+huawei@kernel.org> | 2020-04-14 11:31:49 +0300 |
commit | 54f38fcae536ea202ce7d6a359521492fba30c1f (patch) | |
tree | dd1a2b36d8de0b13702f2716526ad3b91650e090 /Documentation/userspace-api/media/v4l/querycap.rst | |
parent | 5dfb8db56b273740a76e8687ee7efb4b2c0ec83b (diff) | |
download | linux-54f38fcae536ea202ce7d6a359521492fba30c1f.tar.xz |
media: docs: move uAPI book to userspace-api/media
Since 2017, there is an space reserved for userspace API,
created by changeset 1d596dee3862 ("docs: Create a user-space API guide").
As the media subsystem was one of the first subsystems to use
Sphinx, until this patch, we were keeping things on a separate
place.
Let's just use the new location, as having all uAPI altogether
will likely make things easier for developers.
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Diffstat (limited to 'Documentation/userspace-api/media/v4l/querycap.rst')
-rw-r--r-- | Documentation/userspace-api/media/v4l/querycap.rst | 41 |
1 files changed, 41 insertions, 0 deletions
diff --git a/Documentation/userspace-api/media/v4l/querycap.rst b/Documentation/userspace-api/media/v4l/querycap.rst new file mode 100644 index 000000000000..35fba2a9e09b --- /dev/null +++ b/Documentation/userspace-api/media/v4l/querycap.rst @@ -0,0 +1,41 @@ +.. Permission is granted to copy, distribute and/or modify this +.. document under the terms of the GNU Free Documentation License, +.. Version 1.1 or any later version published by the Free Software +.. Foundation, with no Invariant Sections, no Front-Cover Texts +.. and no Back-Cover Texts. A copy of the license is included at +.. Documentation/userspace-api/media/fdl-appendix.rst. +.. +.. TODO: replace it to GFDL-1.1-or-later WITH no-invariant-sections + +.. _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. |