85 lines
3.6 KiB
ReStructuredText
85 lines
3.6 KiB
ReStructuredText
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.. SPDX-License-Identifier: GPL-2.0
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DW100 dewarp driver
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===================
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The Vivante DW100 Dewarp Processor IP core found on i.MX8MP SoC applies a
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programmable geometrical transformation on the input image to correct distortion
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introduced by lenses.
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The transformation function is exposed by the hardware as a grid map with 16x16
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pixel macroblocks indexed using X, Y vertex coordinates.
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::
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Image width
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<--------------------------------------->
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^ .-------.-------.-------.-------.-------.
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| | 16x16 | | | | |
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I | | pixel | | | | |
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m | | block | | | | |
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a | .-------.-------.-------.-------.-------.
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g | | | | | | |
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e | | | | | | |
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h | .-------.-------.-------.-------.-------.
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e | | | | | | |
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i | | | | | | |
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g | | | | | | |
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h | .-------.-------.-------.-------.-------.
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t | | | | | | |
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v '-------'-------'-------'-------'-------'
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Grid of Image Blocks for Dewarping Map
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Each x, y coordinate register uses 16 bits to record the coordinate address in
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an unsigned 12.4 fixed point format (UQ12.4).
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::
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.----------------------.--------..----------------------.--------.
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| 31~20 | 19~16 || 15~4 | 3~0 |
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| (integer) | (frac) || (integer) | (frac) |
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'----------------------'--------''----------------------'--------'
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<-------------------------------><------------------------------->
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Y coordinate X coordinate
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Remap Register Layout
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The dewarping map is set from applications using the
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V4L2_CID_DW100_DEWARPING_16x16_VERTEX_MAP control. The control contains
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an array of u32 values storing (x, y) destination coordinates for each
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vertex of the grid. The x coordinate is stored in the 16 LSBs and the y
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coordinate in the 16 MSBs.
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The number of elements in the array must match the image size:
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.. code-block:: C
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elems = (DIV_ROUND_UP(width, 16) + 1) * (DIV_ROUND_UP(height, 16) + 1);
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If the control has not been set by the application, the driver uses an identity
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map.
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More details on the DW100 hardware operations can be found in
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*chapter 13.15 DeWarp* of IMX8MP_ reference manual.
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The Vivante DW100 m2m driver implements the following driver-specific control:
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``V4L2_CID_DW100_DEWARPING_16x16_VERTEX_MAP (__u32 array)``
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Specifies to DW100 driver its dewarping map (aka LUT) blob as described in
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*chapter 13.15.2.3 Dewarping Remap* of IMX8MP_ reference manual as an U32
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dynamic array. The image is divided into many small 16x16 blocks. If the
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width/height of the image is not divisible by 16, the size of the
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rightmost/bottommost block is the remainder. The dewarping map only saves
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the vertex coordinates of the block. The dewarping grid map is comprised of
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vertex coordinates for x and y. Each x, y coordinate register uses 16 bits
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(UQ12.4) to record the coordinate address, with the Y coordinate in the
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upper bits and X in the lower bits. The driver modifies the dimensions of
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this control when the sink format is changed, to reflect the new input
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resolution.
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.. _IMX8MP: https://www.nxp.com/webapp/Download?colCode=IMX8MPRM
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