There are some monitors, in my case Dell U2413, that report having YCbCr support when plugged in over HDMI. My AMD Radeon RX 570 Series video card sees this YCbCr pixel format and then prefers that over the RGB pixel format. The result is that fonts, graphics and other visuals are pixelated and not smooth in Ubuntu.
This actually is not just a Linux problem. A similar problem exists on macOS with the same monitor hooked up over HDMI. In fact an article by John Ruble on the Atomic Object blog called Fixing the External Monitor Color Problem with My 2018 MacBook Pro attempts to fix the exact same thing.
All of the articles I could find exploring this topic advocate patching the EDID for the monitor. Unfortunately the macOS solution would not work here. Luckily I found a Reddit post that covered how to get it working.
Install the patched EDID (this example uses the pre-patched EDID attached here) and modify GRUB to use the new EDID.
$ sudo mkdir -p /lib/firmware/edid
$ cd /lib/firmware/edid
$ wget https://gist.github.com/RLovelett/171c374be1ad4f14eb22fe4e271b7eeb/raw/edid.bin
$ sudo tee "/etc/initramfs-tools/hooks/edid" > /dev/null <<'EOF'
#!/bin/sh
PREREQ=""
prereqs()
{
echo "$PREREQ"
}
case $1 in
prereqs)
prereqs
exit 0
;;
esac
. /usr/share/initramfs-tools/hook-functions
# Begin real processing below this line
mkdir -p "${DESTDIR}/lib/firmware/edid"
cp -a /lib/firmware/edid/edid.bin "${DESTDIR}/lib/firmware/edid/edid.bin"
exit 0
EOF
$ chmod +x /etc/initramfs-tools/hooks/edid
$ sudo update-initramfs -u
Edit /etc/default/grub
and add drm_kms_helper.edid_firmware=edid/edid.bin
to the end of GRUB_CMDLINE_LINUX_DEFAULT
.
For example:
--- /etc/default/grub 2020-03-19 15:27:24.350222700 -0400
+++ /etc/default/grub 2020-03-19 14:22:58.052179120 -0400
@@ -7,7 +7,7 @@
GRUB_TIMEOUT_STYLE=hidden
GRUB_TIMEOUT=0
GRUB_DISTRIBUTOR=`lsb_release -i -s 2> /dev/null || echo Debian`
-GRUB_CMDLINE_LINUX_DEFAULT="quiet splash"
+GRUB_CMDLINE_LINUX_DEFAULT="quiet splash drm_kms_helper.edid_firmware=edid/edid.bin"
GRUB_CMDLINE_LINUX=""
# Uncomment to enable BadRAM filtering, modify to suit your needs
After saving the changes to /etc/default/grub
run sudo grub-mkconfig -o /boot/grub/grub.cfg
and reboot.
Find your current EDID and copy it to the current working directory.
$ sudo find /sys/devices/pci*/*/*/*/*/*HDMI* -name "*edid*" | head -1 | xargs -I{} cp {} edid.bin
$ sudo apt install -y libwxgtk3.0-dev
$ wget https://sourceforge.net/projects/wxedid/files/wxedid-0.0.19.tar.gz/download
$ tar xvf wxedid-0.0.19.tar.gz
$ cd wxedid-0.0.19
$ ./configure --prefix=$HOME
$ make
$ make install
$HOME/bin/wxEDID
- Open the
edid.bin
file with wxEDID - Find
SPF: Supported features
->vsig_format
-> replace0b01
wih0b00
- Find
CHD: CEA-861 header
-> change the value ofYCbCr420
andYCbCr444
to0
- Find
VSD: Vendor Specific Data Block
-> Change the value ofDC_Y444
to0
- Click
Option
on the panel->Recalc Checksum
- Save patched EDID and exit
Thank you! This has been bothering me for a year in a 4 identical monitor setup with 3xDP 1xHDMI. Finally decided to dig into the depths of the internet to find the answer, and even tried the EDID trick some days ago, but it was missing some of the flags you specified here. Going through the steps you described worked flawlessly.
I also noted the initramfs hook where someone was having a problem with cryptfs (which I have). And you have it here as well.
Worth noting they have a patch for this, but it never did end up in the mainline. https://www.spinics.net/lists/amd-gfx/msg53281.html
Thank you again.