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author | Sakari Ailus <sakari.ailus@linux.intel.com> | 2021-02-01 10:16:03 +0100 |
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committer | Mauro Carvalho Chehab <mchehab+huawei@kernel.org> | 2021-08-04 14:43:50 +0200 |
commit | b9a543364299e09ba236c69acb021ebbf7cebf1a (patch) | |
tree | c1bf41a74d88b37c9609ea0bae82442ce5eb2468 /Documentation/driver-api/media | |
parent | 0368e7d2cd84a90d0518753fac33795e13df553f (diff) | |
download | linux-stable-b9a543364299e09ba236c69acb021ebbf7cebf1a.tar.gz linux-stable-b9a543364299e09ba236c69acb021ebbf7cebf1a.tar.bz2 linux-stable-b9a543364299e09ba236c69acb021ebbf7cebf1a.zip |
media: Documentation: media: Improve camera sensor documentation
Modernise the documentation to make it more precise and update the use of
pixel rate control and various other changes. In particular:
- Use non-proportional font for file names, properties as well as
controls.
- The unit of the HBLANK control is pixels, not lines.
- The unit of PIXEL_RATE control is pixels per second, not Hz.
- Merge common requirements for CSI-2 and parallel busses.
- Include all DT properties needed for assigned clocks.
- Fix referencing the link rate control.
- SMIA driver's new name is CCS driver.
- The PIXEL_RATE control denotes pixel rate on the pixel array on camera
sensors. Do not suggest it is used to tell the maximum pixel rate on the
bus anymore.
- Improve ReST syntax (plain struct and function names).
- Remove the suggestion to use s_power() in receiver drivers.
- Make MIPI website URL use HTTPS, add Wikipedia links to BT.601 and
BT.656.
Fixes: e4cf8c58af75 ("media: Documentation: media: Document how to write camera sensor drivers")
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Reviewed-by: Jacopo Mondi <jacopo@jmondi.org>
Reviewed-by: Andrey Konovalov <andrey.konovalov@linaro.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Diffstat (limited to 'Documentation/driver-api/media')
-rw-r--r-- | Documentation/driver-api/media/camera-sensor.rst | 45 | ||||
-rw-r--r-- | Documentation/driver-api/media/csi2.rst | 94 | ||||
-rw-r--r-- | Documentation/driver-api/media/index.rst | 2 | ||||
-rw-r--r-- | Documentation/driver-api/media/tx-rx.rst | 117 |
4 files changed, 135 insertions, 123 deletions
diff --git a/Documentation/driver-api/media/camera-sensor.rst b/Documentation/driver-api/media/camera-sensor.rst index 7160336aa475..c7d4891bd24e 100644 --- a/Documentation/driver-api/media/camera-sensor.rst +++ b/Documentation/driver-api/media/camera-sensor.rst @@ -3,10 +3,10 @@ Writing camera sensor drivers ============================= -CSI-2 ------ +CSI-2 and parallel (BT.601 and BT.656) busses +--------------------------------------------- -Please see what is written on :ref:`MIPI_CSI_2`. +Please see :ref:`transmitter-receiver`. Handling clocks --------------- @@ -26,15 +26,16 @@ user. ACPI ~~~~ -Read the "clock-frequency" _DSD property to denote the frequency. The driver can -rely on this frequency being used. +Read the ``clock-frequency`` _DSD property to denote the frequency. The driver +can rely on this frequency being used. Devicetree ~~~~~~~~~~ -The currently preferred way to achieve this is using "assigned-clock-rates" -property. See Documentation/devicetree/bindings/clock/clock-bindings.txt for -more information. The driver then gets the frequency using clk_get_rate(). +The currently preferred way to achieve this is using ``assigned-clocks``, +``assigned-clock-parents`` and ``assigned-clock-rates`` properties. See +``Documentation/devicetree/bindings/clock/clock-bindings.txt`` for more +information. The driver then gets the frequency using ``clk_get_rate()``. This approach has the drawback that there's no guarantee that the frequency hasn't been modified directly or indirectly by another driver, or supported by @@ -55,7 +56,7 @@ processing pipeline as one or more sub-devices with different cropping and scaling configurations. The output size of the device is the result of a series of cropping and scaling operations from the device's pixel array's size. -An example of such a driver is the smiapp driver (see drivers/media/i2c/smiapp). +An example of such a driver is the CCS driver (see ``drivers/media/i2c/ccs``). Register list based drivers ~~~~~~~~~~~~~~~~~~~~~~~~~~~ @@ -67,7 +68,7 @@ level are independent. How a driver picks such configuration is based on the format set on a source pad at the end of the device's internal pipeline. Most sensor drivers are implemented this way, see e.g. -drivers/media/i2c/imx319.c for an example. +``drivers/media/i2c/imx319.c`` for an example. Frame interval configuration ---------------------------- @@ -94,9 +95,10 @@ large variety of devices beyond camera sensors. Devices that have no analogue crop, use the full source image size, i.e. pixel array size. Horizontal and vertical blanking are specified by ``V4L2_CID_HBLANK`` and -``V4L2_CID_VBLANK``, respectively. The unit of these controls are lines. The -pixel rate is specified by ``V4L2_CID_PIXEL_RATE`` in the same sub-device. The -unit of that control is Hz. +``V4L2_CID_VBLANK``, respectively. The unit of the ``V4L2_CID_HBLANK`` control +is pixels and the unit of the ``V4L2_CID_VBLANK`` is lines. The pixel rate in +the sensor's **pixel array** is specified by ``V4L2_CID_PIXEL_RATE`` in the same +sub-device. The unit of that control is pixels per second. Register list based drivers need to implement read-only sub-device nodes for the purpose. Devices that are not register list based need these to configure the @@ -125,14 +127,14 @@ general, the device must be powered on at least when its registers are being accessed and when it is streaming. Existing camera sensor drivers may rely on the old -:c:type:`v4l2_subdev_core_ops`->s_power() callback for bridge or ISP drivers to +struct v4l2_subdev_core_ops->s_power() callback for bridge or ISP drivers to manage their power state. This is however **deprecated**. If you feel you need to begin calling an s_power from an ISP or a bridge driver, instead please add runtime PM support to the sensor driver you are using. Likewise, new drivers should not use s_power. Please see examples in e.g. ``drivers/media/i2c/ov8856.c`` and -``drivers/media/i2c/smiapp/smiapp-core.c``. The two drivers work in both ACPI +``drivers/media/i2c/ccs/ccs-core.c``. The two drivers work in both ACPI and DT based systems. Control framework @@ -149,16 +151,3 @@ used to obtain device's power state after the power state transition: The function returns a non-zero value if it succeeded getting the power count or runtime PM was disabled, in either of which cases the driver may proceed to access the device. - -Controls --------- - -For camera sensors that are connected to a bus where transmitter and receiver -require common configuration set by drivers, such as CSI-2 or parallel (BT.601 -or BT.656) bus, the ``V4L2_CID_LINK_FREQ`` control is mandatory on transmitter -drivers. Receiver drivers can use the ``V4L2_CID_LINK_FREQ`` to query the -frequency used on the bus. - -The transmitter drivers should also implement ``V4L2_CID_PIXEL_RATE`` control in -order to tell the maximum pixel rate to the receiver. This is required on raw -camera sensors. diff --git a/Documentation/driver-api/media/csi2.rst b/Documentation/driver-api/media/csi2.rst deleted file mode 100644 index 11c52b0be8b8..000000000000 --- a/Documentation/driver-api/media/csi2.rst +++ /dev/null @@ -1,94 +0,0 @@ -.. SPDX-License-Identifier: GPL-2.0 - -.. _MIPI_CSI_2: - -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/ - -Media bus formats ------------------ - -See :ref:`v4l2-mbus-pixelcode` for details on which media bus formats should -be used for CSI-2 interfaces. - -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 -control 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 * 16 / k / 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. - * - k - - 16 for D-PHY and 7 for C-PHY - -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_get` 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. diff --git a/Documentation/driver-api/media/index.rst b/Documentation/driver-api/media/index.rst index 813d7db59da7..08e206567408 100644 --- a/Documentation/driver-api/media/index.rst +++ b/Documentation/driver-api/media/index.rst @@ -37,7 +37,7 @@ Documentation/userspace-api/media/index.rst rc-core mc-core cec-core - csi2 + tx-rx camera-sensor drivers/index diff --git a/Documentation/driver-api/media/tx-rx.rst b/Documentation/driver-api/media/tx-rx.rst new file mode 100644 index 000000000000..4c8584e7b6f2 --- /dev/null +++ b/Documentation/driver-api/media/tx-rx.rst @@ -0,0 +1,117 @@ +.. SPDX-License-Identifier: GPL-2.0 + +.. _transmitter-receiver: + +Pixel data transmitter and receiver drivers +=========================================== + +V4L2 supports various devices that transmit and receiver pixel data. Examples of +these devices include a camera sensor, a TV tuner and a parallel or a CSI-2 +receiver in an SoC. + +Bus types +--------- + +The following busses are the most common. This section discusses these two only. + +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`: https://www.mipi.org/ + +Parallel +^^^^^^^^ + +`BT.601`_ and `BT.656`_ are the most common parallel busses. + +.. _`BT.601`: https://en.wikipedia.org/wiki/Rec._601 +.. _`BT.656`: https://en.wikipedia.org/wiki/ITU-R_BT.656 + +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. + +Media bus pixel code +^^^^^^^^^^^^^^^^^^^^ + +See :ref:`v4l2-mbus-pixelcode`. + +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 +^^^^^^^^^^^^^^^^^^^^^^^^ + +The struct struct v4l2_subdev_video_ops->s_stream() callback is used by the +receiver driver to control the transmitter driver's streaming state. + + +CSI-2 transmitter drivers +------------------------- + +Pixel rate +^^^^^^^^^^ + +The pixel rate on the bus is calculated as follows:: + + pixel_rate = link_freq * 2 * nr_of_lanes * 16 / k / 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 + - 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 + +.. note:: + + The pixel rate calculated this way is **not** the same thing as the + 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 +^^^^^^^^^^^^^^^^^^^^^^ + +The transmitter drivers must, if possible, configure the CSI-2 transmitter to +*LP-11 or LP-111 mode* whenever the transmitter is powered on but not active, +and maintain *LP-11 or LP-111 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. + +The receiver thus need to be configured to expect LP-11 or LP-111 mode from the +transmitter before the transmitter driver's ``.s_stream()`` op is called. + +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. |