media: Documentation: ccs: Add user documentation for the CCS driver

Add user documentation for the CCS driver. This includes e.g. sub-devices
implemented by the driver.
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>

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

+.. SPDX-License-Identifier: GPL-2.0-only
+
+.. 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.
+
+**Copyright** |copy| 2020 Intel Corporation

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

@@ -31,6 +31,7 @@ For more details see the file COPYING in the source distribution of Linux.
 	:maxdepth: 5
 	:numbered:
 
+	ccs
 	cx2341x-uapi
 	imx-uapi
 	max2175

MAINTAINERS

@@ -11836,6 +11836,7 @@ L:	linux-media@vger.kernel.org
 S:	Maintained
 F:	Documentation/devicetree/bindings/media/i2c/mipi-ccs.yaml
 F:	Documentation/driver-api/media/drivers/ccs/
+F:	Documentation/userspace-api/media/drivers/ccs.rst
 F:	drivers/media/i2c/ccs-pll.c
 F:	drivers/media/i2c/ccs-pll.h
 F:	drivers/media/i2c/ccs/