Documentation/userspace-api/media/v4l/ext-ctrls-dv.rst

Source file repositories/reference/linux-study-clean/Documentation/userspace-api/media/v4l/ext-ctrls-dv.rst

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Documentation/userspace-api/media/v4l/ext-ctrls-dv.rst
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Repository support layer: documentation, build tooling, samples, user-space helper tools, generated initramfs support, licenses, and validation utilities.

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.. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later
.. c:namespace:: V4L

.. _dv-controls:

*******************************
Digital Video Control Reference
*******************************

The Digital Video control class is intended to control receivers and
transmitters for `VGA <http://en.wikipedia.org/wiki/Vga>`__,
`DVI <http://en.wikipedia.org/wiki/Digital_Visual_Interface>`__
(Digital Visual Interface), HDMI (:ref:`hdmi`) and DisplayPort
(:ref:`dp`). These controls are generally expected to be private to
the receiver or transmitter subdevice that implements them, so they are
only exposed on the ``/dev/v4l-subdev*`` device node.

.. note::

   Note that these devices can have multiple input or output pads which are
   hooked up to e.g. HDMI connectors. Even though the subdevice will
   receive or transmit video from/to only one of those pads, the other pads
   can still be active when it comes to EDID (Extended Display
   Identification Data, :ref:`vesaedid`) and HDCP (High-bandwidth Digital
   Content Protection System, :ref:`hdcp`) processing, allowing the
   device to do the fairly slow EDID/HDCP handling in advance. This allows
   for quick switching between connectors.

These pads appear in several of the controls in this section as
bitmasks, one bit for each pad. Bit 0 corresponds to pad 0, bit 1 to pad
1, etc. The maximum value of the control is the set of valid pads.


.. _dv-control-id:

Digital Video Control IDs
=========================

``V4L2_CID_DV_CLASS (class)``
    The Digital Video class descriptor.

``V4L2_CID_DV_TX_HOTPLUG (bitmask)``
    Many connectors have a hotplug pin which is high if EDID information
    is available from the source. This control shows the state of the
    hotplug pin as seen by the transmitter. Each bit corresponds to an
    output pad on the transmitter. If an output pad does not have an
    associated hotplug pin, then the bit for that pad will be 0. This
    read-only control is applicable to DVI-D, HDMI and DisplayPort
    connectors.

``V4L2_CID_DV_TX_RXSENSE (bitmask)``
    Rx Sense is the detection of pull-ups on the TMDS clock lines. This
    normally means that the sink has left/entered standby (i.e. the
    transmitter can sense that the receiver is ready to receive video).
    Each bit corresponds to an output pad on the transmitter. If an
    output pad does not have an associated Rx Sense, then the bit for
    that pad will be 0. This read-only control is applicable to DVI-D
    and HDMI devices.

``V4L2_CID_DV_TX_EDID_PRESENT (bitmask)``
    When the transmitter sees the hotplug signal from the receiver it
    will attempt to read the EDID. If set, then the transmitter has read
    at least the first block (= 128 bytes). Each bit corresponds to an
    output pad on the transmitter. If an output pad does not support
    EDIDs, then the bit for that pad will be 0. This read-only control
    is applicable to VGA, DVI-A/D, HDMI and DisplayPort connectors.

``V4L2_CID_DV_TX_MODE``
    (enum)

Annotation

Implementation Notes