media: Documentation: ccs: Add CCS driver documentation

Document the MIPI CCS driver and the C register definition generator.
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>

Documentation/driver-api/media/drivers/ccs/ccs.rst

+.. 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.
+
+Register definition generator
+-----------------------------
+
+The ccs-regs.txt 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.txt
+
+**Copyright** |copy| 2020 Intel Corporation

Documentation/driver-api/media/drivers/index.rst

@@ -26,6 +26,7 @@ Video4Linux (V4L) drivers
 	tuners
 	vimc-devel
 	zoran
+	ccs/ccs
 
 
 Digital TV drivers