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Diffstat (limited to 'Documentation/driver-api/media/tx-rx.rst')
| -rw-r--r-- | Documentation/driver-api/media/tx-rx.rst | 73 |
1 files changed, 42 insertions, 31 deletions
diff --git a/Documentation/driver-api/media/tx-rx.rst b/Documentation/driver-api/media/tx-rx.rst index e1e9258dd862..22e1b13ecde9 100644 --- a/Documentation/driver-api/media/tx-rx.rst +++ b/Documentation/driver-api/media/tx-rx.rst @@ -6,13 +6,13 @@ Pixel data transmitter and receiver drivers =========================================== V4L2 supports various devices that transmit and receive pixel data. Examples of -these devices include a camera sensor, a TV tuner and a parallel or a CSI-2 -receiver in an SoC. +these devices include a camera sensor, a TV tuner and a parallel, a BT.656 or a +CSI-2 receiver in an SoC. Bus types --------- -The following busses are the most common. This section discusses these two only. +The following buses are the most common. This section discusses these two only. MIPI CSI-2 ^^^^^^^^^^ @@ -22,12 +22,13 @@ the host SoC. It is defined by the `MIPI alliance`_. .. _`MIPI alliance`: https://www.mipi.org/ -Parallel -^^^^^^^^ +Parallel and BT.656 +^^^^^^^^^^^^^^^^^^^ -`BT.601`_ and `BT.656`_ are the most common parallel busses. +The parallel and `BT.656`_ buses transport one bit of data on each clock cycle +per data line. The parallel bus uses synchronisation and other additional +signals whereas BT.656 embeds synchronisation. -.. _`BT.601`: https://en.wikipedia.org/wiki/Rec._601 .. _`BT.656`: https://en.wikipedia.org/wiki/ITU-R_BT.656 Transmitter drivers @@ -35,7 +36,7 @@ Transmitter drivers Transmitter drivers generally need to provide the receiver drivers with the configuration of the transmitter. What is required depends on the type of the -bus. These are common for both busses. +bus. These are common for both buses. Media bus pixel code ^^^^^^^^^^^^^^^^^^^^ @@ -48,12 +49,31 @@ Link frequency The :ref:`V4L2_CID_LINK_FREQ <v4l2-cid-link-freq>` control is used to tell the receiver the frequency of the bus (i.e. it is not the same as the symbol rate). -``.s_stream()`` callback -^^^^^^^^^^^^^^^^^^^^^^^^ +Drivers that do not have user-configurable link frequency should report it +through the ``.get_mbus_config()`` subdev pad operation, in the ``link_freq`` +field of struct v4l2_mbus_config, instead of through controls. + +Receiver drivers should use :c:func:`v4l2_get_link_freq` helper to obtain the +link frequency from the transmitter sub-device. + +``.enable_streams()`` and ``.disable_streams()`` callbacks +^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ -The struct struct v4l2_subdev_video_ops->s_stream() callback is used by the -receiver driver to control the transmitter driver's streaming state. +The struct v4l2_subdev_pad_ops->enable_streams() and struct +v4l2_subdev_pad_ops->disable_streams() callbacks are used by the receiver driver +to control the transmitter driver's streaming state. These callbacks may not be +called directly, but by using ``v4l2_subdev_enable_streams()`` and +``v4l2_subdev_disable_streams()``. + +Stopping the transmitter +^^^^^^^^^^^^^^^^^^^^^^^^ +A transmitter stops sending the stream of images as a result of +calling the ``.disable_streams()`` callback. Some transmitters may stop the +stream at a frame boundary whereas others stop immediately, +effectively leaving the current frame unfinished. The receiver driver +should not make assumptions either way, but function properly in both +cases. CSI-2 transmitter drivers ------------------------- @@ -75,14 +95,15 @@ where * - link_freq - The value of the ``V4L2_CID_LINK_FREQ`` integer64 menu item. * - nr_of_lanes - - Number of data lanes used on the CSI-2 link. This can - be obtained from the OF endpoint configuration. + - Number of data lanes used on the CSI-2 link. * - 2 - Data is transferred on both rising and falling edge of the signal. * - bits_per_sample - Number of bits per sample. * - k - - 16 for D-PHY and 7 for C-PHY + - 16 for D-PHY and 7 for C-PHY. + +Information on whether D-PHY or C-PHY is used, and the value of ``nr_of_lanes``, can be obtained from the OF endpoint configuration. .. note:: @@ -90,8 +111,8 @@ where pixel rate on the camera sensor's pixel array which is indicated by the :ref:`V4L2_CID_PIXEL_RATE <v4l2-cid-pixel-rate>` control. -LP-11 and LP-111 modes -^^^^^^^^^^^^^^^^^^^^^^ +LP-11 and LP-111 states +^^^^^^^^^^^^^^^^^^^^^^^ As part of transitioning to high speed mode, a CSI-2 transmitter typically briefly sets the bus to LP-11 or LP-111 state, depending on the PHY. This period @@ -105,7 +126,7 @@ in software, especially when there is no interrupt telling something is happening. One way to address this is to configure the transmitter side explicitly to LP-11 -or LP-111 mode, which requires support from the transmitter hardware. This is +or LP-111 state, which requires support from the transmitter hardware. This is not universally available. Many devices return to this state once streaming is stopped while the state after power-on is LP-00 or LP-000. @@ -116,18 +137,8 @@ transitioning to streaming state, but not yet start streaming. Similarly, the to call ``.post_streamoff()`` for each successful call of ``.pre_streamon()``. In the context of CSI-2, the ``.pre_streamon()`` callback is used to transition -the transmitter to the LP-11 or LP-111 mode. This also requires powering on the +the transmitter to the LP-11 or LP-111 state. This also requires powering on the device, so this should be only done when it is needed. -Receiver drivers that do not need explicit LP-11 or LP-111 mode setup are waived -from calling the two callbacks. - -Stopping the transmitter -^^^^^^^^^^^^^^^^^^^^^^^^ - -A transmitter stops sending the stream of images as a result of -calling the ``.s_stream()`` callback. Some transmitters may stop the -stream at a frame boundary whereas others stop immediately, -effectively leaving the current frame unfinished. The receiver driver -should not make assumptions either way, but function properly in both -cases. +Receiver drivers that do not need explicit LP-11 or LP-111 state setup are +waived from calling the two callbacks. |