linux/Documentation/EDID/HOWTO.txt
<<
>>
Prefs
   1In the good old days when graphics parameters were configured explicitly
   2in a file called xorg.conf, even broken hardware could be managed.
   3
   4Today, with the advent of Kernel Mode Setting, a graphics board is
   5either correctly working because all components follow the standards -
   6or the computer is unusable, because the screen remains dark after
   7booting 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.
  13Adding the kernel parameter "nomodeset" helps in most cases, but causes
  14restrictions later on.
  15
  16As a remedy for such situations, the kernel configuration item
  17CONFIG_DRM_LOAD_EDID_FIRMWARE was introduced. It allows to provide an
  18individually prepared or corrected EDID data set in the /lib/firmware
  19directory 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
  21commonly used screen resolutions (1024x768, 1280x1024, 1680x1050,
  221920x1080) as binary blobs, but the kernel source tree does not contain
  23code to create these data. In order to elucidate the origin of the
  24built-in binary EDID blobs and to facilitate the creation of individual
  25data for a specific misbehaving monitor, commented sources and a
  26Makefile environment are given here.
  27
  28To create binary EDID and C source code files from the existing data
  29material, simply type "make".
  30
  31If you want to create your own EDID file, copy the file 1024x768.S and
  32replace the settings with your own data. The CRC value in the last line
  33  #define CRC 0x55
  34is a bit tricky. After a first version of the binary data set is
  35created, it must be be checked with the "edid-decode" utility which will
  36most probably complain about a wrong CRC. Fortunately, the utility also
  37displays the correct CRC which must then be inserted into the source
  38file. After the make procedure is repeated, the EDID data set is ready
  39to be used.
  40
lxr.linux.no kindly hosted by Redpill Linpro AS, provider of Linux consulting and operations services since 1995.