tjh.dev
Linux kernel mirror (for testing)
git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
kernel
os
linux
1.. SPDX-License-Identifier: GPL-2.0
2
3DW100 dewarp driver
4===================
5
6The Vivante DW100 Dewarp Processor IP core found on i.MX8MP SoC applies a
7programmable geometrical transformation on the input image to correct distortion
8introduced by lenses.
9
10The transformation function is exposed by the hardware as a grid map with 16x16
11pixel macroblocks indexed using X, Y vertex coordinates.
12::
13
14 Image width
15 <--------------------------------------->
16
17 ^ .-------.-------.-------.-------.-------.
18 | | 16x16 | | | | |
19 I | | pixel | | | | |
20 m | | block | | | | |
21 a | .-------.-------.-------.-------.-------.
22 g | | | | | | |
23 e | | | | | | |
24 | | | | | | |
25 h | .-------.-------.-------.-------.-------.
26 e | | | | | | |
27 i | | | | | | |
28 g | | | | | | |
29 h | .-------.-------.-------.-------.-------.
30 t | | | | | | |
31 | | | | | | |
32 | | | | | | |
33 v '-------'-------'-------'-------'-------'
34
35 Grid of Image Blocks for Dewarping Map
36
37
38Each x, y coordinate register uses 16 bits to record the coordinate address in
39an unsigned 12.4 fixed point format (UQ12.4).
40::
41
42 .----------------------.--------..----------------------.--------.
43 | 31~20 | 19~16 || 15~4 | 3~0 |
44 | (integer) | (frac) || (integer) | (frac) |
45 '----------------------'--------''----------------------'--------'
46 <-------------------------------><------------------------------->
47 Y coordinate X coordinate
48
49 Remap Register Layout
50
51The dewarping map is set from applications using the
52V4L2_CID_DW100_DEWARPING_16x16_VERTEX_MAP control. The control contains
53an array of u32 values storing (x, y) destination coordinates for each
54vertex of the grid. The x coordinate is stored in the 16 LSBs and the y
55coordinate in the 16 MSBs.
56
57The number of elements in the array must match the image size:
58
59.. code-block:: C
60
61 elems = (DIV_ROUND_UP(width, 16) + 1) * (DIV_ROUND_UP(height, 16) + 1);
62
63If the control has not been set by the application, the driver uses an identity
64map.
65
66More details on the DW100 hardware operations can be found in
67*chapter 13.15 DeWarp* of IMX8MP_ reference manual.
68
69The Vivante DW100 m2m driver implements the following driver-specific control:
70
71``V4L2_CID_DW100_DEWARPING_16x16_VERTEX_MAP (__u32 array)``
72 Specifies to DW100 driver its dewarping map (aka LUT) blob as described in
73 *chapter 13.15.2.3 Dewarping Remap* of IMX8MP_ reference manual as an U32
74 dynamic array. The image is divided into many small 16x16 blocks. If the
75 width/height of the image is not divisible by 16, the size of the
76 rightmost/bottommost block is the remainder. The dewarping map only saves
77 the vertex coordinates of the block. The dewarping grid map is comprised of
78 vertex coordinates for x and y. Each x, y coordinate register uses 16 bits
79 (UQ12.4) to record the coordinate address, with the Y coordinate in the
80 upper bits and X in the lower bits. The driver modifies the dimensions of
81 this control when the sink format is changed, to reflect the new input
82 resolution.
83
84.. _IMX8MP: https://www.nxp.com/webapp/Download?colCode=IMX8MPRM