.. SPDX-License-Identifier: GPL-2.0 MIPI CSI-2 ========== CSI-2 is a data bus intended for transferring images from cameras to the host SoC. It is defined by the `MIPI alliance`_. .. _`MIPI alliance`: http://www.mipi.org/ Transmitter drivers ------------------- CSI-2 transmitter, such as a sensor or a TV tuner, drivers need to provide the CSI-2 receiver with information on the CSI-2 bus configuration. These include the V4L2_CID_LINK_FREQ and V4L2_CID_PIXEL_RATE controls and (:c:type:`v4l2_subdev_video_ops`->s_stream() callback). These interface elements must be present on the sub-device represents the CSI-2 transmitter. The V4L2_CID_LINK_FREQ control is used to tell the receiver driver the frequency (and not the symbol rate) of the link. The V4L2_CID_PIXEL_RATE is may be used by the receiver to obtain the pixel rate the transmitter uses. The :c:type:`v4l2_subdev_video_ops`->s_stream() callback provides an ability to start and stop the stream. The value of the V4L2_CID_PIXEL_RATE is calculated as follows:: pixel_rate = link_freq * 2 * nr_of_lanes / bits_per_sample where .. list-table:: variables in pixel rate calculation :header-rows: 1 * - variable or constant - description * - 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. * - 2 - Two bits are transferred per clock cycle per lane. * - bits_per_sample - Number of bits per sample. The transmitter drivers must, if possible, configure the CSI-2 transmitter to *LP-11 mode* whenever the transmitter is powered on but not active, and maintain *LP-11 mode* until stream on. Only at stream on should the transmitter activate the clock on the clock lane and transition to *HS mode*. Some transmitters do this automatically but some have to be explicitly programmed to do so, and some are unable to do so altogether due to hardware constraints. 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 ---------------- Before the receiver driver may enable the CSI-2 transmitter by using the :c:type:`v4l2_subdev_video_ops`->s_stream(), it must have powered the transmitter up by using the :c:type:`v4l2_subdev_core_ops`->s_power() callback. This may take place either indirectly by using :c:func:`v4l2_pipeline_pm_use` or directly. Formats ------- The media bus pixel codes document parallel formats. Should the pixel data be transported over a serial bus, the media bus pixel code that describes a parallel format that transfers a sample on a single clock cycle is used. |