How to fix low screen resolution

Sometimes when you connect a device to a monitor (external or integrated), you may experience an unexpected low resolution that you cannot change via system setting GUI of your desktop environment: only lower resolutions could be available.

This can happen especially if you are using a VGA-to-HDMI converter to connect an old pc to a newer monitor. If the comunication is unidirectional, from input (e.g., a mini pc supporting only VGA) to output (e.g. an external monitor supporting only HDMI), the monitor won't be able to send EDID data packets which containts info regarding its capabilities.

In such cases, you can have to grab the EDID data from another pc connected to this monitor or online, if you are lucky enough to find it.

Firstly, you should verify that the graphic card(s) of your pc can match the recommended resolution of your monitor: typically, 1920x1080 at 60 refresh rate (a standard also know as 1080p, Full HD or FHD,). For Intel cards, see here.

Once this is verified, you may try to just add the the intended resolution (let's tick to the default scenario, i.e. 1920x1080) with xrandr:

# show available resolutions for common display types (VGA, HDMI, etc.)
xrandr
# generate correct params for the target resolution
cvt 1920 1080 60
# pass the above params to the next command
xrandr --newmode "1920x1080_60.00"  173.00  1920 2048 2248 2576  1080 1083 1088 1120 -hsync +vsync
# make available the new resolution for the intended display type
xrandr --addmode VGA-1 "1920x1080_60.00"
xrandr --output VGA-1 --mode "1920x1080_60.00"
# go to the system settings GUI and select the resolution you have just configured if it's not still active after last command is executed

If this solved your problem, you have just to put these commands in an executable file sourced when the X session starts. Put this file in one of the following directories:

  • ~/.profile
  • /etc/profile.d

If this did not solve the problem for you, some extra work is needed: you will have to manually retrieve the EDID file and set it in a Xorg config file or append it to the kernel parameters in the boot loader's boot selection menu.

To parse EDID info, install the read-edid package: apt install read-edid

To retrieve the EDID file, you have two options:

  • find it in the EDID repository of the The Linux Hardware Project by searching for the model name of your monitor
  • grab it from another pc connected to the monitor by running the following command (substitute card1-HDMI-A-1 with the DRM device found on this second pc): 
    :~$ edid-decode </sys/class/drm/card1-HDMI-A-1/edid
edid-decode (hex):

00 ff ff ff ff ff ff 00 09 d1 51 79 45 54 00 00
1f 1d 01 03 80 35 1e 78 2a 05 61 a7 56 52 9c 27
0f 50 54 a5 6b 80 d1 c0 81 c0 81 00 81 80 a9 c0
b3 00 d1 cf 01 01 02 3a 80 18 71 38 2d 40 58 2c
45 00 0f 28 21 00 00 1e 00 00 00 ff 00 31 38 4b
30 30 30 33 33 30 31 51 0a 20 00 00 00 fd 00 30
4b 1e 53 15 00 0a 20 20 20 20 20 20 00 00 00 fc
00 42 65 6e 51 20 45 57 32 34 38 30 0a 20 01 ba

02 03 44 f1 4f 90 1f 05 14 04 13 03 12 07 16 15
01 06 11 02 23 09 07 07 83 01 00 00 e2 00 d5 68
03 0c 00 30 00 38 44 00 67 d8 5d c4 01 78 80 00
68 1a 00 00 01 01 30 4b e6 e3 05 c3 01 e6 06 05
01 61 5a 26 02 3a 80 18 71 38 2d 40 58 2c 45 00
0f 28 21 00 00 1e 01 1d 00 72 51 d0 1e 20 6e 28
55 00 0f 28 21 00 00 1e 8c 0a d0 8a 20 e0 2d 10
10 3e 96 00 0f 28 21 00 00 18 00 00 00 00 00 e8

----------------

Block 0, Base EDID:
EDID Structure Version & Revision: 1.3
Vendor & Product Identification:
    Manufacturer: BNQ
    Model: 31057
    Serial Number: 21573
    Made in: week 31 of 2019
[...]

Once you have it, use the first hexadecimal block at the beginning of the output of the command to generate the binary file:

$ HEXSTR="\
00 ff ff ff ff ff ff 00 09 d1 51 79 45 54 00 00\
1f 1d 01 03 80 35 1e 78 2a 05 61 a7 56 52 9c 27\
0f 50 54 a5 6b 80 d1 c0 81 c0 81 00 81 80 a9 c0\
b3 00 d1 cf 01 01 02 3a 80 18 71 38 2d 40 58 2c\
45 00 0f 28 21 00 00 1e 00 00 00 ff 00 31 38 4b\
30 30 30 33 33 30 31 51 0a 20 00 00 00 fd 00 30\
4b 1e 53 15 00 0a 20 20 20 20 20 20 00 00 00 fc\
00 42 65 6e 51 20 45 57 32 34 38 30 0a 20 01 ba";

$ echo -en $(echo "$HEXSTR" | sed -E 's/([0-9abcdef][0-9abcdef])[[:space:]]?/\\x\1/g') > edid.bin
# check that the file is readable
$ edid-decode edid.bin

In order to apply it only to a specific connector with a specific resolution, force this kernel mode setting (KMS) by copying the file (edid.bin in the example) into /usr/lib/firmware (create it if it does not exists) with a proper name and parent folder according to the following pattern: CONNECTOR:edid/RESOLUTION.bin (e.g. /usr/lib/firmware/VGA-1:edid/1920x1080.bin).

You now have two options to make this file available to the display manager (e.g. SDDM):

  • adding a config file to the xorg.conf.d directory with the relevant info, as described here
  • modifying the Linux Kernel parameters to include a directive for reading the EDID file at boot time.

The first option is lengthy and requires you to understand how to properly configure Xorg.

The second is quicker but error-prone, so be extra-careful if going through the following steps:

  • reboot the system, wait for the system to restart and then press and hold the Esc key until the GRUB menu appears
  • if it doesn't appear at all after multiple retries, chanches are that you must set a longer timeout for the GRUB
  • press e when the menu appears and add the drm.edid_firmware argument to the end of the line starting with linux:
linux /boot/vmlinuz-linux root=UUID=0a3407de-014b-458b-b5c1-848e92a327a3 rw [...] drm.edid_firmware=VGA-1:edid/1920x1080.bin

Boot the system to verify if the change had the desired effect.

If so, make the change permanent by editing the /etc/default/grub to set GRUB_CMDLINE_LINUX_DEFAULT option to the new parameter (e.g. GRUB_CMDLINE_LINUX_DEFAULT="drm.edid_firmware=VGA-1:edid/your_edid.bin") and then regenerating the GRUB config with: grub-mkconfig -o /boot/grub/grub.cfg.

Reboot to verify that the change works across system restarts.

References: