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HOWTO.txt

HOWTO.txt 2.1 KB
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  1. In the good old days when graphics parameters were configured explicitly
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  2. in a file called xorg.conf, even broken hardware could be managed.
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  3. 

  4. Today, with the advent of Kernel Mode Setting, a graphics board is
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  5. either correctly working because all components follow the standards -
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  6. or the computer is unusable, because the screen remains dark after
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  7. booting or it displays the wrong area. Cases when this happens are:
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  8. - The graphics board does not recognize the monitor.
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  9. - The graphics board is unable to detect any EDID data.
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  10. - The graphics board incorrectly forwards EDID data to the driver.
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  11. - The monitor sends no or bogus EDID data.
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  12. - A KVM sends its own EDID data instead of querying the connected monitor.
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  13. Adding the kernel parameter "nomodeset" helps in most cases, but causes
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  14. restrictions later on.
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  15. 

  16. As a remedy for such situations, the kernel configuration item
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  17. CONFIG_DRM_LOAD_EDID_FIRMWARE was introduced. It allows to provide an
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  18. individually prepared or corrected EDID data set in the /lib/firmware
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  19. directory from where it is loaded via the firmware interface. The code
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  20. (see drivers/gpu/drm/drm_edid_load.c) contains built-in data sets for
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  21. commonly used screen resolutions (1024x768, 1280x1024, 1680x1050,
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  22. 1920x1080) as binary blobs, but the kernel source tree does not contain
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  23. code to create these data. In order to elucidate the origin of the
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  24. built-in binary EDID blobs and to facilitate the creation of individual
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  25. data for a specific misbehaving monitor, commented sources and a
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  26. Makefile environment are given here.
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  27. 

  28. To create binary EDID and C source code files from the existing data
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  29. material, simply type "make".
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  30. 

  31. If you want to create your own EDID file, copy the file 1024x768.S and
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  32. replace the settings with your own data. The CRC value in the last line
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  33.   #define CRC 0x55
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  34. is a bit tricky. After a first version of the binary data set is
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  35. created, it must be be checked with the "edid-decode" utility which will
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  36. most probably complain about a wrong CRC. Fortunately, the utility also
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  37. displays the correct CRC which must then be inserted into the source
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  38. file. After the make procedure is repeated, the EDID data set is ready
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  39. to be used.
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  40.