@@ -1,8 +1,14 @@
.. SPDX-License-Identifier: GPL-2.0
+.. _media_writing_camera_sensor_drivers:
+
Writing camera sensor drivers
=============================
+This document covers the in-kernel APIs only. For the best practices on
+userspace API implementation in camera sensor drivers, please see
+:ref:`media_using_camera_sensor_drivers`.
+
CSI-2 and parallel (BT.601 and BT.656) busses
---------------------------------------------
@@ -34,7 +40,8 @@ Devicetree
The preferred way to achieve this is using ``assigned-clocks``,
``assigned-clock-parents`` and ``assigned-clock-rates`` properties. See the
-`clock device tree bindings <https://github.com/devicetree-org/dt-schema/blob/main/dtschema/schemas/clock/clock.yaml>`_
+`clock device tree bindings
+<https://github.com/devicetree-org/dt-schema/blob/main/dtschema/schemas/clock/clock.yaml>`_
for more information. The driver then gets the frequency using
``clk_get_rate()``.
@@ -85,9 +92,7 @@ PM instead. If you feel you need to begin calling ``.s_power()`` from an ISP or
a bridge driver, instead add runtime PM support to the sensor driver you are
using and drop its ``.s_power()`` handler.
-See examples of runtime PM handling in e.g. ``drivers/media/i2c/ov8856.c`` and
-``drivers/media/i2c/ccs/ccs-core.c``. The two drivers work in both ACPI and DT
-based systems.
+Please also see :ref:`examples <media-camera-sensor-examples>`.
Control framework
~~~~~~~~~~~~~~~~~
@@ -104,99 +109,39 @@ 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.
-Frame size
-----------
-
-There are two distinct ways to configure the frame size produced by camera
-sensors.
-
-Freely configurable camera sensor drivers
-~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-
-Freely configurable camera sensor drivers expose the device's internal
-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 CCS driver (see ``drivers/media/i2c/ccs``).
-
-Register list based drivers
-~~~~~~~~~~~~~~~~~~~~~~~~~~~
-
-Register list based drivers generally, instead of able to configure the device
-they control based on user requests, are limited to a number of preset
-configurations that combine a number of different parameters that on hardware
-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.
-
-Frame interval configuration
-----------------------------
-
-There are two different methods for obtaining possibilities for different frame
-intervals as well as configuring the frame interval. Which one to implement
-depends on the type of the device.
-
-Raw camera sensors
-~~~~~~~~~~~~~~~~~~
-
-Instead of a high level parameter such as frame interval, the frame interval is
-a result of the configuration of a number of camera sensor implementation
-specific parameters. Luckily, these parameters tend to be the same for more or
-less all modern raw camera sensors.
-
-The frame interval is calculated using the following equation::
-
- frame interval = (analogue crop width + horizontal blanking) *
- (analogue crop height + vertical blanking) / pixel rate
-
-The formula is bus independent and is applicable for raw timing parameters on
-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 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
-device's internal processing pipeline.
-
-The first entity in the linear pipeline is the pixel array. The pixel array may
-be followed by other entities that are there to allow configuring binning,
-skipping, scaling or digital crop :ref:`v4l2-subdev-selections`.
-
-USB cameras etc. devices
-~~~~~~~~~~~~~~~~~~~~~~~~
-
-USB video class hardware, as well as many cameras offering a similar higher
-level interface natively, generally use the concept of frame interval (or frame
-rate) on device level in firmware or hardware. This means lower level controls
-implemented by raw cameras may not be used on uAPI (or even kAPI) to control the
-frame interval on these devices.
-
Rotation, orientation and flipping
----------------------------------
-Some systems have the camera sensor mounted upside down compared to its natural
-mounting rotation. In such cases, drivers shall expose the information to
-userspace with the :ref:`V4L2_CID_CAMERA_SENSOR_ROTATION
-<v4l2-camera-sensor-rotation>` control.
-
-Sensor drivers shall also report the sensor's mounting orientation with the
-:ref:`V4L2_CID_CAMERA_SENSOR_ORIENTATION <v4l2-camera-sensor-orientation>`.
-
Use ``v4l2_fwnode_device_parse()`` to obtain rotation and orientation
information from system firmware and ``v4l2_ctrl_new_fwnode_properties()`` to
register the appropriate controls.
-Sensor drivers that have any vertical or horizontal flips embedded in the
-register programming sequences shall initialize the V4L2_CID_HFLIP and
-V4L2_CID_VFLIP controls with the values programmed by the register sequences.
-The default values of these controls shall be 0 (disabled). Especially these
-controls shall not be inverted, independently of the sensor's mounting
-rotation.
+.. _media-camera-sensor-examples:
+
+Example drivers
+---------------
+
+Features implemented by sensor drivers vary, and depending on the set of
+supported features and other qualities, particular sensor drivers better serve
+the purpose of an example. The following drivers are known to be good examples:
+
+.. flat-table:: Example sensor drivers
+ :header-rows: 0
+ :widths: 1 1 1 2
+
+ * - Driver name
+ - File(s)
+ - Driver type
+ - Example topic
+ * - CCS
+ - ``drivers/media/i2c/ccs/``
+ - Freely configurable
+ - Power management (ACPI and DT), UAPI
+ * - imx219
+ - ``drivers/media/i2c/imx219.c``
+ - Register list based
+ - Power management (DT), UAPI, mode selection
+ * - imx319
+ - ``drivers/media/i2c/imx319.c``
+ - Register list based
+ - Power management (ACPI and DT)
new file mode 100644
@@ -0,0 +1,104 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+.. _media_using_camera_sensor_drivers:
+
+Using camera sensor drivers
+===========================
+
+This section describes common practices for how the V4L2 sub-device interface is
+used to control the camera sensor drivers.
+
+You may also find :ref:`media_writing_camera_sensor_drivers` useful.
+
+Frame size
+----------
+
+There are two distinct ways to configure the frame size produced by camera
+sensors.
+
+Freely configurable camera sensor drivers
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Freely configurable camera sensor drivers expose the device's internal
+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 CCS driver.
+
+Register list based drivers
+~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Register list based drivers generally, instead of able to configure the device
+they control based on user requests, are limited to a number of preset
+configurations that combine a number of different parameters that on hardware
+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.
+
+Frame interval configuration
+----------------------------
+
+There are two different methods for obtaining possibilities for different frame
+intervals as well as configuring the frame interval. Which one to implement
+depends on the type of the device.
+
+Raw camera sensors
+~~~~~~~~~~~~~~~~~~
+
+Instead of a high level parameter such as frame interval, the frame interval is
+a result of the configuration of a number of camera sensor implementation
+specific parameters. Luckily, these parameters tend to be the same for more or
+less all modern raw camera sensors.
+
+The frame interval is calculated using the following equation::
+
+ frame interval = (analogue crop width + horizontal blanking) *
+ (analogue crop height + vertical blanking) / pixel rate
+
+The formula is bus independent and is applicable for raw timing parameters on
+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 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
+device's internal processing pipeline.
+
+The first entity in the linear pipeline is the pixel array. The pixel array may
+be followed by other entities that are there to allow configuring binning,
+skipping, scaling or digital crop, see :ref:`VIDIOC_SUBDEV_G_SELECTION
+<VIDIOC_SUBDEV_G_SELECTION>`.
+
+USB cameras etc. devices
+~~~~~~~~~~~~~~~~~~~~~~~~
+
+USB video class hardware, as well as many cameras offering a similar higher
+level interface natively, generally use the concept of frame interval (or frame
+rate) on device level in firmware or hardware. This means lower level controls
+implemented by raw cameras may not be used on uAPI (or even kAPI) to control the
+frame interval on these devices.
+
+Rotation, orientation and flipping
+----------------------------------
+
+Some systems have the camera sensor mounted upside down compared to its natural
+mounting rotation. In such cases, drivers shall expose the information to
+userspace with the :ref:`V4L2_CID_CAMERA_SENSOR_ROTATION
+<v4l2-camera-sensor-rotation>` control.
+
+Sensor drivers shall also report the sensor's mounting orientation with the
+:ref:`V4L2_CID_CAMERA_SENSOR_ORIENTATION <v4l2-camera-sensor-orientation>`.
+
+Sensor drivers that have any vertical or horizontal flips embedded in the
+register programming sequences shall initialize the :ref:`V4L2_CID_HFLIP
+<v4l2-cid-hflip>` and :ref:`V4L2_CID_VFLIP <v4l2-cid-vflip>` controls with the
+values programmed by the register sequences. The default values of these
+controls shall be 0 (disabled). Especially these controls shall not be inverted,
+independently of the sensor's mounting rotation.
@@ -32,6 +32,7 @@ For more details see the file COPYING in the source distribution of Linux.
:numbered:
aspeed-video
+ camera-sensor
ccs
cx2341x-uapi
dw100
@@ -143,9 +143,13 @@ Control IDs
recognise the difference between digital and analogue gain use
controls ``V4L2_CID_DIGITAL_GAIN`` and ``V4L2_CID_ANALOGUE_GAIN``.
+.. _v4l2-cid-hflip:
+
``V4L2_CID_HFLIP`` ``(boolean)``
Mirror the picture horizontally.
+.. _v4l2-cid-vflip:
+
``V4L2_CID_VFLIP`` ``(boolean)``
Mirror the picture vertically.