111 lines
3.9 KiB
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111 lines
3.9 KiB
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.. SPDX-License-Identifier: GPL-2.0-only
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.. include:: <isonum.txt>
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MIPI CCS camera sensor driver
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=============================
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The MIPI CCS camera sensor driver is a generic driver for `MIPI CCS
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<https://www.mipi.org/specifications/camera-command-set>`_ compliant
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camera sensors. It exposes three sub-devices representing the pixel array,
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the binner and the scaler.
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As the capabilities of individual devices vary, the driver exposes
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interfaces based on the capabilities that exist in hardware.
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Pixel Array sub-device
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----------------------
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The pixel array sub-device represents the camera sensor's pixel matrix, as well
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as analogue crop functionality present in many compliant devices. The analogue
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crop is configured using the ``V4L2_SEL_TGT_CROP`` on the source pad (0) of the
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entity. The size of the pixel matrix can be obtained by getting the
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``V4L2_SEL_TGT_NATIVE_SIZE`` target.
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Binner
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------
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The binner sub-device represents the binning functionality on the sensor. For
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that purpose, selection target ``V4L2_SEL_TGT_COMPOSE`` is supported on the
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sink pad (0).
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Additionally, if a device has no scaler or digital crop functionality, the
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source pad (1) expses another digital crop selection rectangle that can only
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crop at the end of the lines and frames.
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Scaler
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------
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The scaler sub-device represents the digital crop and scaling functionality of
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the sensor. The V4L2 selection target ``V4L2_SEL_TGT_CROP`` is used to
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configure the digital crop on the sink pad (0) when digital crop is supported.
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Scaling is configured using selection target ``V4L2_SEL_TGT_COMPOSE`` on the
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sink pad (0) as well.
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Additionally, if the scaler sub-device exists, its source pad (1) exposes
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another digital crop selection rectangle that can only crop at the end of the
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lines and frames.
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Digital and analogue crop
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-------------------------
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Digital crop functionality is referred to as cropping that effectively works by
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dropping some data on the floor. Analogue crop, on the other hand, means that
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the cropped information is never retrieved. In case of camera sensors, the
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analogue data is never read from the pixel matrix that are outside the
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configured selection rectangle that designates crop. The difference has an
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effect in device timing and likely also in power consumption.
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Private controls
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----------------
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The MIPI CCS driver implements a number of private controls under
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``V4L2_CID_USER_BASE_CCS`` to control the MIPI CCS compliant camera sensors.
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Analogue gain model
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~~~~~~~~~~~~~~~~~~~
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The CCS defines an analogue gain model where the gain can be calculated using
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the following formula:
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gain = m0 * x + c0 / (m1 * x + c1)
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Either m0 or c0 will be zero. The constants that are device specific, can be
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obtained from the following controls:
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V4L2_CID_CCS_ANALOGUE_GAIN_M0
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V4L2_CID_CCS_ANALOGUE_GAIN_M1
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V4L2_CID_CCS_ANALOGUE_GAIN_C0
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V4L2_CID_CCS_ANALOGUE_GAIN_C1
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The analogue gain (``x`` in the formula) is controlled through
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``V4L2_CID_ANALOGUE_GAIN`` in this case.
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Alternate analogue gain model
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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The CCS defines another analogue gain model called alternate analogue gain. In
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this case, the formula to calculate actual gain consists of linear and
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exponential parts:
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gain = linear * 2 ^ exponent
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The ``linear`` and ``exponent`` factors can be set using the
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``V4L2_CID_CCS_ANALOGUE_LINEAR_GAIN`` and
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``V4L2_CID_CCS_ANALOGUE_EXPONENTIAL_GAIN`` controls, respectively
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Shading correction
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~~~~~~~~~~~~~~~~~~
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The CCS standard supports lens shading correction. The feature can be controlled
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using ``V4L2_CID_CCS_SHADING_CORRECTION``. Additionally, the luminance
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correction level may be changed using
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``V4L2_CID_CCS_LUMINANCE_CORRECTION_LEVEL``, where value 0 indicates no
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correction and 128 indicates correcting the luminance in corners to 10 % less
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than in the centre.
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Shading correction needs to be enabled for luminance correction level to have an
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effect.
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**Copyright** |copy| 2020 Intel Corporation
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