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Commit bac4b7c3 authored by Carsten Emde's avatar Carsten Emde Committed by Dave Airlie
Browse files

drm: Load EDID: Explain better how to write your own EDID firmware 



A description was lacking how to write an EDID firmware file that
corresponds to a given X11 setting.

Signed-off-by: default avatarCarsten Emde <C.Emde@osadl.org>
Reviewed-by: default avatarAdam Jackson <ajax@redhat.com>
Signed-off-by: default avatarDave Airlie <airlied@redhat.com>
parent b5cc6c03

Documentation/EDID/HOWTO.txt

+23 −4
Original line number Diff line number Diff line
@@ -28,11 +28,30 @@ 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 and

replace the settings with your own data. The CRC value in the last line

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

is a bit tricky. After a first version of the binary data set is

created, it must be be checked with the "edid-decode" utility which will

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