mirror of
https://github.com/torvalds/linux.git
synced 2024-11-25 05:32:00 +00:00
40 lines
2.1 KiB
Plaintext
40 lines
2.1 KiB
Plaintext
|
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, 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 and
|
||
|
|
replace the settings with your own data. 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
|
||
|
|
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.
|