pyrox.dev
1# Customizing display configuration {#module-hardware-display}
2
3This section describes how to customize display configuration using:
4- kernel modes
5- EDID files
6
7Example situations it can help you with:
8- display controllers (external hardware) not advertising EDID at all,
9- misbehaving graphics drivers,
10- loading custom display configuration before the Display Manager is running,
11
12## Forcing display modes {#module-hardware-display-modes}
13
14In case of very wrong monitor controller and/or video driver combination you can
15[force the display to be enabled](https://mjmwired.net/kernel/Documentation/fb/modedb.txt#41)
16and skip some driver-side checks by adding `video=<OUTPUT>:e` to `boot.kernelParams`.
17This is exactly the case with [`amdgpu` drivers](https://gitlab.freedesktop.org/drm/amd/-/issues/615#note_1987392)
18
19```nix
20{
21 # force enabled output to skip `amdgpu` checks
22 hardware.display.outputs."DP-1".mode = "e";
23 # completely disable output no matter what is connected to it
24 hardware.display.outputs."VGA-2".mode = "d";
25
26 /* equals
27 boot.kernelParams = [ "video=DP-1:e" "video=VGA-2:d" ];
28 */
29}
30```
31
32## Crafting custom EDID files {#module-hardware-display-edid-custom}
33
34To make custom EDID binaries discoverable you should first create a derivation storing them at
35`$out/lib/firmware/edid/` and secondly add that derivation to `hardware.display.edid.packages` NixOS option:
36
37```nix
38{
39 hardware.display.edid.packages = [
40 (pkgs.runCommand "edid-custom" {} ''
41 mkdir -p $out/lib/firmware/edid
42 base64 -d > "$out/lib/firmware/edid/custom1.bin" <<'EOF'
43 <insert your base64 encoded EDID file here `base64 < /sys/class/drm/card0-.../edid`>
44 EOF
45 base64 -d > "$out/lib/firmware/edid/custom2.bin" <<'EOF'
46 <insert your base64 encoded EDID file here `base64 < /sys/class/drm/card1-.../edid`>
47 EOF
48 '')
49 ];
50}
51```
52
53There are 2 options significantly easing preparation of EDID files:
54- `hardware.display.edid.linuxhw`
55- `hardware.display.edid.modelines`
56
57## Assigning EDID files to displays {#module-hardware-display-edid-assign}
58
59To assign available custom EDID binaries to your monitor (video output) use `hardware.display.outputs."<NAME>".edid` option.
60Under the hood it adds `drm.edid_firmware` entry to `boot.kernelParams` NixOS option for each configured output:
61
62```nix
63{
64 hardware.display.outputs."VGA-1".edid = "custom1.bin";
65 hardware.display.outputs."VGA-2".edid = "custom2.bin";
66 /* equals:
67 boot.kernelParams = [ "drm.edid_firmware=VGA-1:edid/custom1.bin,VGA-2:edid/custom2.bin" ];
68 */
69}
70```
71
72## Pulling files from linuxhw/EDID database {#module-hardware-display-edid-linuxhw}
73
74`hardware.display.edid.linuxhw` utilizes `pkgs.linuxhw-edid-fetcher` to extract EDID files
75from https://github.com/linuxhw/EDID based on simple string/regexp search identifying exact entries:
76
77```nix
78{
79 hardware.display.edid.linuxhw."PG278Q_2014" = [ "PG278Q" "2014" ];
80
81 /* equals:
82 hardware.display.edid.packages = [
83 (pkgs.linuxhw-edid-fetcher.override {
84 displays = {
85 "PG278Q_2014" = [ "PG278Q" "2014" ];
86 };
87 })
88 ];
89 */
90}
91```
92
93
94## Using XFree86 Modeline definitions {#module-hardware-display-edid-modelines}
95
96`hardware.display.edid.modelines` utilizes `pkgs.edid-generator` package allowing you to
97conveniently use [`XFree86 Modeline`](https://en.wikipedia.org/wiki/XFree86_Modeline) entries as EDID binaries:
98
99```nix
100{
101 hardware.display.edid.modelines."PG278Q_60" = " 241.50 2560 2608 2640 2720 1440 1443 1448 1481 -hsync +vsync";
102 hardware.display.edid.modelines."PG278Q_120" = " 497.75 2560 2608 2640 2720 1440 1443 1448 1525 +hsync -vsync";
103
104 /* equals:
105 hardware.display.edid.packages = [
106 (pkgs.edid-generator.overrideAttrs {
107 clean = true;
108 modelines = ''
109 Modeline "PG278Q_60" 241.50 2560 2608 2640 2720 1440 1443 1448 1481 -hsync +vsync
110 Modeline "PG278Q_120" 497.75 2560 2608 2640 2720 1440 1443 1448 1525 +hsync -vsync
111 '';
112 })
113 ];
114 */
115}
116```
117
118## Complete example for Asus PG278Q {#module-hardware-display-pg278q}
119
120And finally this is a complete working example for a 2014 (first) batch of [Asus PG278Q monitor with `amdgpu` drivers](https://gitlab.freedesktop.org/drm/amd/-/issues/615#note_1987392):
121
122```nix
123{
124 hardware.display.edid.modelines."PG278Q_60" = " 241.50 2560 2608 2640 2720 1440 1443 1448 1481 -hsync +vsync";
125 hardware.display.edid.modelines."PG278Q_120" = " 497.75 2560 2608 2640 2720 1440 1443 1448 1525 +hsync -vsync";
126
127 hardware.display.outputs."DP-1".edid = "PG278Q_60.bin";
128 hardware.display.outputs."DP-1".mode = "e";
129}
130```