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- .. SPDX-License-Identifier: GPL-2.0
- ====
- EDID
- ====
- 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 (800x600, 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" in tools/edid/.
- 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 vsyncstart-vdisp
- #define YPULSE vsyncend-vsyncstart
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