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