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

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

Signed-off-by: Carsten Emde <C.Emde@osadl.org>
Reviewed-by: Adam Jackson <ajax@redhat.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>
This commit is contained in:
Carsten Emde 2012-07-19 15:54:25 +00:00 committed by Dave Airlie
parent b5cc6c0387
commit bac4b7c3b5
1 changed files with 23 additions and 4 deletions
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27
Documentation/EDID/HOWTO.txt
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@ -28,11 +28,30 @@ Makefile environment are given here.
To create binary EDID and C source code files from the existing data To create binary EDID and C source code files from the existing data
material, simply type "make". material, simply type "make".
If you want to create your own EDID file, copy the file 1024x768.S and If you want to create your own EDID file, copy the file 1024x768.S,
replace the settings with your own data. The CRC value in the last line 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 #define CRC 0x55
is a bit tricky. After a first version of the binary data set is also 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 created, it must be checked with the "edid-decode" utility which will
most probably complain about a wrong CRC. Fortunately, the utility also most probably complain about a wrong CRC. Fortunately, the utility also
displays the correct CRC which must then be inserted into the source 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 file. After the make procedure is repeated, the EDID data set is ready