Arc B580 limited to 4k at 60hz refresh rate through HDMI with Ubuntu 25.10 on LG TV

[AndersA]

Hi,

I just purchased the Arc B850 (AsRock Challenger 12GB OC) and installed it into a new build running a fresh install of Ubuntu 25.10 (AM5 socket motherboard, running a Ryzen 5 7600). Unfortunately, I cannot seem to get the refresh rate to go above 60hz at 4k through HDMI to my LG TV. The highest resolution that allows 120hz is 2560 x 1440 (16:9), with neither 4096 x 2160 (9:5) nor 3840 x 2160 (16:9) offering a refresh above 60hz.

My previous GPU worked at 4k 120hz HDMI with the same TV, so I do not think it's the cable nor the TV that's at fault. I have tried updating to the latest Intel Arc drivers without any luck, although this shouldn't be necessary since the update page claims that "Ubuntu 25.10 provides native support for Lunar Lake and Battlemage". ReBAR and 4G decoding are enabled in BIOS. 

Any ideas as to what I can do to get it working? I only found one similar thread in the forum but it did not offer any solutions that worked for me. The user had the same issue with the refresh rate limited to 4k at 60 hz.

Kind regards,

AA 

[AndersA]

Hi,

Quick update!

On windows 11 the problem was the same until I switched the color depth from 8 bit to 12 bit using Intel Graphics Command Center (IGCC). Now it works. The default color depth was set to 8 bit and that appears to be why the display did not allow 120 hz at 4k. I also had the option of choosing 10 bit in IGCC but I have not tried if that works.

Since I do not have Ubuntu right now, and I do not know if Ubuntu allows switching between 8, 10, and/or 12 bit, I hope someone else with the issue on Ubuntu (or other Linux distro) can test it out. It might just work as a solution to them.

Kind regards,

AA

[AndersA]

Another update. I tried the latest version of Fedora (KDE) and despite Fedora allowing color bit depth above 8, I am unable to get 120 HZ at 4k. 

This is very unfortunate since Linux is on the way up and might be the future for the average end user.

[CaNeBuRy23]

well, you already did half the heavy lifting here. And good call on testing Windows too. So here’s the real tea, Your Arc B580 isn’t actually the problem, Ubuntu is defaulting your HDMI output to 8-bit color, and at 4K that caps the available bandwidth to 60 Hz. Once you bumped it to 12-bit on Windows, boom, suddenly 4K 120 Hz unlocked. That lines up perfectly with HDMI 2.1 bandwidth behavior on Arc cards. 

Linux doesn’t always expose color-depth options in GUI settings, but you can force the mode manually. Try these:

Check what color formats your TV is reporting. Open terminal:

xrandr --verbose  Look for the HDMI output block

Try forcing 10-bit/12-bit output. Intel GPUs usually accept this via xrandr:

xrandr --output HDMI-1 --set "max bpc" 12

(If your HDMI port uses a different name, replace HDMI-1 with what xrandr lists.)

Then re-apply the 4K 120 Hz mode:

xrandr --output HDMI-1 --mode 3840x2160 --rate 120

Force YCbCr 4:2:0 (higher efficiency, same visual look at 4K 120 Hz)

Some TVs especially LG unlock 120 Hz easier in this color format:

xrandr --output HDMI-1 --set "Broadcast RGB" "Limited 16:235"

Ubuntu 25.10 should support Battlemage, but sometimes it ships slightly older Mesa builds. Run:

sudo apt update && sudo apt upgrade

Keep in mind that Arc HDMI 2.1 supports 4K 120 Hz only when bandwidth is enough. 8-bit RGB at 4K is too heavy → capped at 60 Hz. 10/12-bit or YCbCr reduces bandwidth → unlocks 120 Hz. Windows IGCC auto-switches this. Ubuntu doesn’t, so you gotta tell it manually.

[RomanV]

hey @CaNeBuRy23, 

how to do this `Force YCbCr 4:2:0` and how to undo it? 😁

I am trying to get my setup work 7680x2160 @240 or 120Hz. So far got only 60Hz by this xrandr magic, I am new to it.

Also, is there difference in configuration for DP and HDMI of this parameters? (I'm starting to get a feeling there is)

Thanks in advance!

[Bruceee31]

Force YCbCr 4:2:0 basically tells your GPU to compress the color info a bit so it can push crazy resolutions or refresh rates without choking the cable. Think of it like squeezing the video to fit that 7680×2160 goodness at higher Hz. 

To turn it on, depends on your setup:

• NVIDIA on Linux? Hit up nvidia-settings or slap ForceYCbCr420=1 in your X config.

• AMD/Intel? Might be in your driver settings or through some xrandr magic.

To undo it, just disable that setting or remove the line and restart. About DP vs HDMI yeah, there’s a difference. DisplayPort’s got more bandwidth, so you might not even need 4:2:0 there. HDMI? Might have to force it if you’re pushing 120Hz/240Hz at 8K. To try 7680×2160 at 120Hz or 240Hz, first check your display name with xrandr, then generate a modeline using cvt 7680 2160 120 (or 240), add it with xrandr --newmode and attach it to your output using xrandr --addmode <DISPLAY> "7680x2160_120.00", then apply it with xrandr --output <DISPLAY> --mode "7680x2160_120.00"; if the refresh rate fails on HDMI, you may need to force YCbCr 4:2:0 via your driver settings to reduce bandwidth, and you can check results or errors with xrandr --verbose or dmesg | grep -i drm.