1.. SPDX-License-Identifier: GPL-2.0 2 3==== 4EDID 5==== 6 7In the good old days when graphics parameters were configured explicitly 8in a file called xorg.conf, even broken hardware could be managed. 9 10Today, with the advent of Kernel Mode Setting, a graphics board is 11either correctly working because all components follow the standards - 12or the computer is unusable, because the screen remains dark after 13booting or it displays the wrong area. Cases when this happens are: 14- The graphics board does not recognize the monitor. 15- The graphics board is unable to detect any EDID data. 16- The graphics board incorrectly forwards EDID data to the driver. 17- The monitor sends no or bogus EDID data. 18- A KVM sends its own EDID data instead of querying the connected monitor. 19Adding the kernel parameter "nomodeset" helps in most cases, but causes 20restrictions later on. 21 22As a remedy for such situations, the kernel configuration item 23CONFIG_DRM_LOAD_EDID_FIRMWARE was introduced. It allows to provide an 24individually prepared or corrected EDID data set in the /lib/firmware 25directory from where it is loaded via the firmware interface. The code 26(see drivers/gpu/drm/drm_edid_load.c) contains built-in data sets for 27commonly used screen resolutions (800x600, 1024x768, 1280x1024, 1600x1200, 281680x1050, 1920x1080) as binary blobs, but the kernel source tree does 29not contain code to create these data. In order to elucidate the origin 30of the built-in binary EDID blobs and to facilitate the creation of 31individual data for a specific misbehaving monitor, commented sources 32and a Makefile environment are given here. 33 34To create binary EDID and C source code files from the existing data 35material, simply type "make". 36 37If you want to create your own EDID file, copy the file 1024x768.S, 38replace the settings with your own data and add a new target to the 39Makefile. Please note that the EDID data structure expects the timing 40values in a different way as compared to the standard X11 format. 41 42X11: 43 HTimings: 44 hdisp hsyncstart hsyncend htotal 45 VTimings: 46 vdisp vsyncstart vsyncend vtotal 47 48EDID:: 49 50 #define XPIX hdisp 51 #define XBLANK htotal-hdisp 52 #define XOFFSET hsyncstart-hdisp 53 #define XPULSE hsyncend-hsyncstart 54 55 #define YPIX vdisp 56 #define YBLANK vtotal-vdisp 57 #define YOFFSET vsyncstart-vdisp 58 #define YPULSE vsyncend-vsyncstart 59