Documentation/EDID/HOWTO.txt - maze/linux - Git at Google

 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 (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".

 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 (63+(vsyncstart-vdisp))
 #define YPULSE (63+(vsyncend-vsyncstart))

 The CRC value in the last line
   #define CRC 0x55
 also is a bit tricky. After a first version of the binary data set is
 created, it must be checked with the "edid-decode" utility which will
 most probably complain about a wrong CRC. Fortunately, the utility also
 displays the correct CRC which must then be inserted into the source
 file. After the make procedure is repeated, the EDID data set is ready
 to be used.
	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 (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".

	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 (63+(vsyncstart-vdisp))
	#define YPULSE (63+(vsyncend-vsyncstart))

	The CRC value in the last line
	#define CRC 0x55
	also is a bit tricky. After a first version of the binary data set is
	created, it must be checked with the "edid-decode" utility which will
	most probably complain about a wrong CRC. Fortunately, the utility also
	displays the correct CRC which must then be inserted into the source
	file. After the make procedure is repeated, the EDID data set is ready
	to be used.