xref: /openbmc/linux/Documentation/driver-api/media/drivers/ccs/ccs.rst (revision 1ac731c529cd4d6adbce134754b51ff7d822b145)

.. SPDX-License-Identifier: GPL-2.0-only OR BSD-3-Clause

.. include:: <isonum.txt>

MIPI CCS camera sensor driver
=============================

The MIPI CCS camera sensor driver is a generic driver for `MIPI CCS
<https://www.mipi.org/specifications/camera-command-set>`_ compliant
camera sensors. It exposes three sub-devices representing the pixel array,
the binner and the scaler.

As the capabilities of individual devices vary, the driver exposes
interfaces based on the capabilities that exist in hardware.

Pixel Array sub-device
----------------------

The pixel array sub-device represents the camera sensor's pixel matrix, as well
as analogue crop functionality present in many compliant devices. The analogue
crop is configured using the ``V4L2_SEL_TGT_CROP`` on the source pad (0) of the
entity. The size of the pixel matrix can be obtained by getting the
``V4L2_SEL_TGT_NATIVE_SIZE`` target.

Binner
------

The binner sub-device represents the binning functionality on the sensor. For
that purpose, selection target ``V4L2_SEL_TGT_COMPOSE`` is supported on the
sink pad (0).

Additionally, if a device has no scaler or digital crop functionality, the
source pad (1) expses another digital crop selection rectangle that can only
crop at the end of the lines and frames.

Scaler
------

The scaler sub-device represents the digital crop and scaling functionality of
the sensor. The V4L2 selection target ``V4L2_SEL_TGT_CROP`` is used to
configure the digital crop on the sink pad (0) when digital crop is supported.
Scaling is configured using selection target ``V4L2_SEL_TGT_COMPOSE`` on the
sink pad (0) as well.

Additionally, if the scaler sub-device exists, its source pad (1) exposes
another digital crop selection rectangle that can only crop at the end of the
lines and frames.

Digital and analogue crop
-------------------------

Digital crop functionality is referred to as cropping that effectively works by
dropping some data on the floor. Analogue crop, on the other hand, means that
the cropped information is never retrieved. In case of camera sensors, the
analogue data is never read from the pixel matrix that are outside the
configured selection rectangle that designates crop. The difference has an
effect in device timing and likely also in power consumption.

CCS static data
---------------

The MIPI CCS driver supports CCS static data for all compliant devices,
including not just those compliant with CCS 1.1 but also CCS 1.0 and SMIA(++).
For CCS the file names are formed as

	ccs/ccs-sensor-vvvv-mmmm-rrrr.fw (sensor) and
	ccs/ccs-module-vvvv-mmmm-rrrr.fw (module).

For SMIA++ compliant devices the corresponding file names are

	ccs/smiapp-sensor-vv-mmmm-rr.fw (sensor) and
	ccs/smiapp-module-vv-mmmm-rrrr.fw (module).

For SMIA (non-++) compliant devices the static data file name is

	ccs/smia-sensor-vv-mmmm-rr.fw (sensor).

vvvv or vv denotes MIPI and SMIA manufacturer IDs respectively, mmmm model ID
and rrrr or rr revision number.

Register definition generator
-----------------------------

The ccs-regs.asc file contains MIPI CCS register definitions that are used
to produce C source code files for definitions that can be better used by
programs written in C language. As there are many dependencies between the
produced files, please do not modify them manually as it's error-prone and
in vain, but instead change the script producing them.

Usage
~~~~~

Conventionally the script is called this way to update the CCS driver
definitions:

.. code-block:: none

	$ Documentation/driver-api/media/drivers/ccs/mk-ccs-regs -k \
		-e drivers/media/i2c/ccs/ccs-regs.h \
		-L drivers/media/i2c/ccs/ccs-limits.h \
		-l drivers/media/i2c/ccs/ccs-limits.c \
		-c Documentation/driver-api/media/drivers/ccs/ccs-regs.asc

CCS PLL calculator
==================

The CCS PLL calculator is used to compute the PLL configuration, given sensor's
capabilities as well as board configuration and user specified configuration. As
the configuration space that encompasses all these configurations is vast, the
PLL calculator isn't entirely trivial. Yet it is relatively simple to use for a
driver.

The PLL model implemented by the PLL calculator corresponds to MIPI CCS 1.1.

.. kernel-doc:: drivers/media/i2c/ccs-pll.h

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