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baa293e9 | 1 | .. SPDX-License-Identifier: GPL-2.0 |
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2 | |
3 | ==== | |
4 | EDID | |
5 | ==== | |
6 | ||
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7 | In the good old days when graphics parameters were configured explicitly |
8 | in a file called xorg.conf, even broken hardware could be managed. | |
9 | ||
10 | Today, with the advent of Kernel Mode Setting, a graphics board is | |
11 | either correctly working because all components follow the standards - | |
12 | or the computer is unusable, because the screen remains dark after | |
13 | booting or it displays the wrong area. Cases when this happens are: | |
1733ec77 | 14 | |
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15 | - The graphics board does not recognize the monitor. |
16 | - The graphics board is unable to detect any EDID data. | |
17 | - The graphics board incorrectly forwards EDID data to the driver. | |
18 | - The monitor sends no or bogus EDID data. | |
19 | - A KVM sends its own EDID data instead of querying the connected monitor. | |
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21 | Adding the kernel parameter "nomodeset" helps in most cases, but causes |
22 | restrictions later on. | |
23 | ||
24 | As a remedy for such situations, the kernel configuration item | |
25 | CONFIG_DRM_LOAD_EDID_FIRMWARE was introduced. It allows to provide an | |
26 | individually prepared or corrected EDID data set in the /lib/firmware | |
27 | directory from where it is loaded via the firmware interface. The code | |
28 | (see drivers/gpu/drm/drm_edid_load.c) contains built-in data sets for | |
4cbe1bfa | 29 | commonly used screen resolutions (800x600, 1024x768, 1280x1024, 1600x1200, |
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30 | 1680x1050, 1920x1080) as binary blobs, but the kernel source tree does |
31 | not contain code to create these data. In order to elucidate the origin | |
32 | of the built-in binary EDID blobs and to facilitate the creation of | |
33 | individual data for a specific misbehaving monitor, commented sources | |
34 | and a Makefile environment are given here. | |
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35 | |
36 | To create binary EDID and C source code files from the existing data | |
b4ce545f | 37 | material, simply type "make" in tools/edid/. |
da0df92b | 38 | |
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39 | If you want to create your own EDID file, copy the file 1024x768.S, |
40 | replace the settings with your own data and add a new target to the | |
41 | Makefile. Please note that the EDID data structure expects the timing | |
42 | values in a different way as compared to the standard X11 format. | |
43 | ||
44 | X11: | |
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45 | HTimings: |
46 | hdisp hsyncstart hsyncend htotal | |
47 | VTimings: | |
48 | vdisp vsyncstart vsyncend vtotal | |
49 | ||
50 | EDID:: | |
51 | ||
52 | #define XPIX hdisp | |
53 | #define XBLANK htotal-hdisp | |
54 | #define XOFFSET hsyncstart-hdisp | |
55 | #define XPULSE hsyncend-hsyncstart | |
56 | ||
57 | #define YPIX vdisp | |
58 | #define YBLANK vtotal-vdisp | |
59 | #define YOFFSET vsyncstart-vdisp | |
60 | #define YPULSE vsyncend-vsyncstart |