Commit | Line | Data |
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da0df92b CE |
1 | In the good old days when graphics parameters were configured explicitly |
2 | in a file called xorg.conf, even broken hardware could be managed. | |
3 | ||
4 | Today, with the advent of Kernel Mode Setting, a graphics board is | |
5 | either correctly working because all components follow the standards - | |
6 | or the computer is unusable, because the screen remains dark after | |
7 | booting or it displays the wrong area. Cases when this happens are: | |
8 | - The graphics board does not recognize the monitor. | |
9 | - The graphics board is unable to detect any EDID data. | |
10 | - The graphics board incorrectly forwards EDID data to the driver. | |
11 | - The monitor sends no or bogus EDID data. | |
12 | - A KVM sends its own EDID data instead of querying the connected monitor. | |
13 | Adding the kernel parameter "nomodeset" helps in most cases, but causes | |
14 | restrictions later on. | |
15 | ||
16 | As a remedy for such situations, the kernel configuration item | |
17 | CONFIG_DRM_LOAD_EDID_FIRMWARE was introduced. It allows to provide an | |
18 | individually prepared or corrected EDID data set in the /lib/firmware | |
19 | directory from where it is loaded via the firmware interface. The code | |
20 | (see drivers/gpu/drm/drm_edid_load.c) contains built-in data sets for | |
21 | commonly used screen resolutions (1024x768, 1280x1024, 1680x1050, | |
22 | 1920x1080) as binary blobs, but the kernel source tree does not contain | |
23 | code to create these data. In order to elucidate the origin of the | |
24 | built-in binary EDID blobs and to facilitate the creation of individual | |
25 | data for a specific misbehaving monitor, commented sources and a | |
26 | Makefile environment are given here. | |
27 | ||
28 | To create binary EDID and C source code files from the existing data | |
29 | material, simply type "make". | |
30 | ||
31 | If you want to create your own EDID file, copy the file 1024x768.S and | |
32 | replace the settings with your own data. The CRC value in the last line | |
33 | #define CRC 0x55 | |
34 | is a bit tricky. After a first version of the binary data set is | |
35 | created, it must be be checked with the "edid-decode" utility which will | |
36 | most probably complain about a wrong CRC. Fortunately, the utility also | |
37 | displays the correct CRC which must then be inserted into the source | |
38 | file. After the make procedure is repeated, the EDID data set is ready | |
39 | to be used. |