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 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. 20 21Adding the kernel parameter "nomodeset" helps in most cases, but causes 22restrictions later on. 23 24As a remedy for such situations, the kernel configuration item 25CONFIG_DRM_LOAD_EDID_FIRMWARE was introduced. It allows to provide an 26individually prepared or corrected EDID data set in the /lib/firmware 27directory 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 29commonly used screen resolutions (800x600, 1024x768, 1280x1024, 1600x1200, 301680x1050, 1920x1080) as binary blobs, but the kernel source tree does 31not contain code to create these data. In order to elucidate the origin 32of the built-in binary EDID blobs and to facilitate the creation of 33individual data for a specific misbehaving monitor, commented sources 34and a Makefile environment are given here. 35 36To create binary EDID and C source code files from the existing data 37material, simply type "make" in tools/edid/. 38 39If you want to create your own EDID file, copy the file 1024x768.S, 40replace the settings with your own data and add a new target to the 41Makefile. Please note that the EDID data structure expects the timing 42values in a different way as compared to the standard X11 format. 43 44X11: 45 HTimings: 46 hdisp hsyncstart hsyncend htotal 47 VTimings: 48 vdisp vsyncstart vsyncend vtotal 49 50EDID:: 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 61