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diff --git a/Documentation/userspace-api/media/drivers/ccs.rst b/Documentation/userspace-api/media/drivers/ccs.rst new file mode 100644 index 000000000..161cb65f4 --- /dev/null +++ b/Documentation/userspace-api/media/drivers/ccs.rst @@ -0,0 +1,110 @@ +.. 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. + +Private controls +---------------- + +The MIPI CCS driver implements a number of private controls under +``V4L2_CID_USER_BASE_CCS`` to control the MIPI CCS compliant camera sensors. + +Analogue gain model +~~~~~~~~~~~~~~~~~~~ + +The CCS defines an analogue gain model where the gain can be calculated using +the following formula: + + gain = m0 * x + c0 / (m1 * x + c1) + +Either m0 or c0 will be zero. The constants that are device specific, can be +obtained from the following controls: + + V4L2_CID_CCS_ANALOGUE_GAIN_M0 + V4L2_CID_CCS_ANALOGUE_GAIN_M1 + V4L2_CID_CCS_ANALOGUE_GAIN_C0 + V4L2_CID_CCS_ANALOGUE_GAIN_C1 + +The analogue gain (``x`` in the formula) is controlled through +``V4L2_CID_ANALOGUE_GAIN`` in this case. + +Alternate analogue gain model +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +The CCS defines another analogue gain model called alternate analogue gain. In +this case, the formula to calculate actual gain consists of linear and +exponential parts: + + gain = linear * 2 ^ exponent + +The ``linear`` and ``exponent`` factors can be set using the +``V4L2_CID_CCS_ANALOGUE_LINEAR_GAIN`` and +``V4L2_CID_CCS_ANALOGUE_EXPONENTIAL_GAIN`` controls, respectively + +Shading correction +~~~~~~~~~~~~~~~~~~ + +The CCS standard supports lens shading correction. The feature can be controlled +using ``V4L2_CID_CCS_SHADING_CORRECTION``. Additionally, the luminance +correction level may be changed using +``V4L2_CID_CCS_LUMINANCE_CORRECTION_LEVEL``, where value 0 indicates no +correction and 128 indicates correcting the luminance in corners to 10 % less +than in the centre. + +Shading correction needs to be enabled for luminance correction level to have an +effect. + +**Copyright** |copy| 2020 Intel Corporation |