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

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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>
This commit is contained in:
Sakari Ailus 2020-11-13 17:12:28 +01:00 committed by Mauro Carvalho Chehab
parent cd9f145dab
commit db08f69ef8
3 changed files with 61 additions and 0 deletions
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59
Documentation/userspace-api/media/drivers/ccs.rst Normal file
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.. 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

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

1
MAINTAINERS
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@ -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/