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diff --git a/Documentation/admin-guide/edid.rst b/Documentation/admin-guide/edid.rst new file mode 100644 index 000000000..80deeb21a --- /dev/null +++ b/Documentation/admin-guide/edid.rst @@ -0,0 +1,60 @@ +.. SPDX-License-Identifier: GPL-2.0 + +==== +EDID +==== + +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 (800x600, 1024x768, 1280x1024, 1600x1200, +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" in tools/edid/. + +If you want to create your own EDID file, copy the file 1024x768.S, +replace the settings with your own data and add a new target to the +Makefile. Please note that the EDID data structure expects the timing +values in a different way as compared to the standard X11 format. + +X11: + HTimings: + hdisp hsyncstart hsyncend htotal + VTimings: + vdisp vsyncstart vsyncend vtotal + +EDID:: + + #define XPIX hdisp + #define XBLANK htotal-hdisp + #define XOFFSET hsyncstart-hdisp + #define XPULSE hsyncend-hsyncstart + + #define YPIX vdisp + #define YBLANK vtotal-vdisp + #define YOFFSET vsyncstart-vdisp + #define YPULSE vsyncend-vsyncstart |