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60 lines
2.3 KiB
60 lines
2.3 KiB
.. SPDX-License-Identifier: GPL-2.0 |
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==== |
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EDID |
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==== |
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In the good old days when graphics parameters were configured explicitly |
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in a file called xorg.conf, even broken hardware could be managed. |
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Today, with the advent of Kernel Mode Setting, a graphics board is |
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either correctly working because all components follow the standards - |
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or the computer is unusable, because the screen remains dark after |
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booting or it displays the wrong area. Cases when this happens are: |
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- The graphics board does not recognize the monitor. |
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- The graphics board is unable to detect any EDID data. |
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- The graphics board incorrectly forwards EDID data to the driver. |
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- The monitor sends no or bogus EDID data. |
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- A KVM sends its own EDID data instead of querying the connected monitor. |
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Adding the kernel parameter "nomodeset" helps in most cases, but causes |
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restrictions later on. |
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As a remedy for such situations, the kernel configuration item |
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CONFIG_DRM_LOAD_EDID_FIRMWARE was introduced. It allows to provide an |
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individually prepared or corrected EDID data set in the /lib/firmware |
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directory from where it is loaded via the firmware interface. The code |
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(see drivers/gpu/drm/drm_edid_load.c) contains built-in data sets for |
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commonly used screen resolutions (800x600, 1024x768, 1280x1024, 1600x1200, |
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1680x1050, 1920x1080) as binary blobs, but the kernel source tree does |
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not contain code to create these data. In order to elucidate the origin |
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of the built-in binary EDID blobs and to facilitate the creation of |
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individual data for a specific misbehaving monitor, commented sources |
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and a Makefile environment are given here. |
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To create binary EDID and C source code files from the existing data |
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material, simply type "make" in tools/edid/. |
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If you want to create your own EDID file, copy the file 1024x768.S, |
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replace the settings with your own data and add a new target to the |
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Makefile. Please note that the EDID data structure expects the timing |
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values in a different way as compared to the standard X11 format. |
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X11: |
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HTimings: |
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hdisp hsyncstart hsyncend htotal |
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VTimings: |
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vdisp vsyncstart vsyncend vtotal |
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EDID:: |
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#define XPIX hdisp |
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#define XBLANK htotal-hdisp |
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#define XOFFSET hsyncstart-hdisp |
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#define XPULSE hsyncend-hsyncstart |
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#define YPIX vdisp |
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#define YBLANK vtotal-vdisp |
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#define YOFFSET vsyncstart-vdisp |
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#define YPULSE vsyncend-vsyncstart
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