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