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Based on kernel version 3.15.4. Page generated on 2014-07-07 09:02 EST.

1	In the good old days when graphics parameters were configured explicitly
2	in a file called xorg.conf, even broken hardware could be managed.
3	
4	Today, with the advent of Kernel Mode Setting, a graphics board is
5	either correctly working because all components follow the standards -
6	or the computer is unusable, because the screen remains dark after
7	booting 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.
13	Adding the kernel parameter "nomodeset" helps in most cases, but causes
14	restrictions later on.
15	
16	As a remedy for such situations, the kernel configuration item
17	CONFIG_DRM_LOAD_EDID_FIRMWARE was introduced. It allows to provide an
18	individually prepared or corrected EDID data set in the /lib/firmware
19	directory 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
21	commonly used screen resolutions (1024x768, 1280x1024, 1600x1200,
22	1680x1050, 1920x1080) as binary blobs, but the kernel source tree does
23	not contain code to create these data. In order to elucidate the origin
24	of the built-in binary EDID blobs and to facilitate the creation of
25	individual data for a specific misbehaving monitor, commented sources
26	and a Makefile environment are given here.
27	
28	To create binary EDID and C source code files from the existing data
29	material, simply type "make".
30	
31	If you want to create your own EDID file, copy the file 1024x768.S,
32	replace the settings with your own data and add a new target to the
33	Makefile. Please note that the EDID data structure expects the timing
34	values in a different way as compared to the standard X11 format.
35	
36	X11:
37	HTimings:  hdisp hsyncstart hsyncend htotal
38	VTimings:  vdisp vsyncstart vsyncend vtotal
39	
40	EDID:
41	#define XPIX hdisp
42	#define XBLANK htotal-hdisp
43	#define XOFFSET hsyncstart-hdisp
44	#define XPULSE hsyncend-hsyncstart
45	
46	#define YPIX vdisp
47	#define YBLANK vtotal-vdisp
48	#define YOFFSET (63+(vsyncstart-vdisp))
49	#define YPULSE (63+(vsyncend-vsyncstart))
50	
51	The CRC value in the last line
52	  #define CRC 0x55
53	also is a bit tricky. After a first version of the binary data set is
54	created, it must be checked with the "edid-decode" utility which will
55	most probably complain about a wrong CRC. Fortunately, the utility also
56	displays the correct CRC which must then be inserted into the source
57	file. After the make procedure is repeated, the EDID data set is ready
58	to be used.
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