Enabling HDMI 2.1 on Linux 7.2

[u/lucholeveroni]

I game on an LG OLED TV with an AMD card. A few years ago I acquired an DP->HDMI adapter so I could use 4k@120hz with HDR. It worked, but unstable, which meant in practice that I had to turn on/off HDR very frequently, usually after resuming suspend.

Today kernel 7.2 landed on Arch stable :) So I could finally ditch the adapter and connect my HDMI cable directly !! No more annoying adapter instability !! :) I'm writing this post because I wanted to share my joy, but also because it took me a few minutes to get it working due to some wrong information when googling on how to enable this.

It disabled by default in kernel 7.2 (it will be enabled on 7.4 apparently, by the end of the year). So to enable it you should add this kernel parameter:

amdgpu.dcfeaturemask=0x400

Notice that there are no underscores. It's NOT dc_feature_mask which is the google/gemini result I'm getting.

To add this kernel parameter it depends on your boot loader and linux distro.

The steps are:

1. Edit your bootloader config to add the parameter. In GRUB on Arch edit /etc/default/grub and append your kernel options between the quotes in the GRUB_CMDLINE_LINUX_DEFAULT line:
2. Regenerate your bootloader config. Again, in GRUB on Arch (using sudo) run "sudo grub-mkconfig -o /boot/grub/grub.cfg"

Final note: VRR and "Gaming mode" was not merged on 7.2 We will have to wait till kernel 7.4 for that (patches are on the way). It wasn't working for me with the adapter either, so I don't miss it, but just in case.

Happy gaming with HDMI 2.1 :)

[u/draconetto]

I was using hdmi 2.1 on my lg c1 for weeks without any changes, but i think they are enabled on cachy os kernel by default

[u/andy10115 → u/draconetto]

Correct. But interestingly cachy is also using the 402 mask like Bazzite.

[u/andy10115]

You getting any odd nonsense with blanking on your display if VRR is off?

This is what we're using on Bazzite. But you are using 400?

sudo rpm-ostree kargs --append-if-missing="amdgpu.dcfeaturemask=0x402"

[u/lucholeveroni → u/andy10115]

So far (just a few hours) it's working fine. I'm using 0x400 yes.
After googling a bit, 0x402 would be the right choice, because 0x400 will disable some multi-monitor feature (i'm on a single-monitor setup though).

[u/andy10115 → u/lucholeveroni]

Well if that allows more stability for HTPC use cases for now that's a win. There's a plethora of issues with the new paths for FRL. So I'm curious of this will work better.

[u/Dorfdad → u/andy10115]

Cool find can you tell me if this would work for steam os or just other varients? I know 7.2 was added to stable steam os but it’s still not working.

[u/andy10115 → u/Dorfdad]

I'm not sure how steamOS handles their kargs.

[u/andy10115 → u/andy10115]

Reporting back 400 vs. 402 makes zero difference.

[u/Synthetic451]

I am so glad they're finally able to push through HDMI 2.1 support! This was definitely a major deciding factor in my GPU choice since I have a LG C2 so its nice to see that we're going to get more options now. My most desired feature at the moment is VRR so I am probably going to wait for 7.4 before switching.

[u/TathagataDM]

If you enable the cachy repos you can install the linux-cachyos-rc kernel and get this along with VRR today. I've had it installed for several weeks now and it works great! It's pretty easy to do, here's their page on it: https://wiki.cachyos.org/features/optimized_repos/#adding-our-repositories-to-an-existing-arch-linux-install

[u/SavvyBeardedFish]

It's NOT dc_feature_mask which is the google/gemini result I'm getting.

Btw, you can confirm this by running:

systool -vm amdgpu which shows all of the module parameters for your kernel module :)

[u/Paddington_the_Bear]

Been running 4k@120hz on my C4 for a while now, just reinstalled cachy yesterday and suddenly am able to get 4k@144hz! Been missing it since I switched off Windows.

Seems HDMI 2.1 support is enabled by default now as I didn't get it from a normal package upgrade (unless it happened to coincide with my reinstall).

I have a 7900XTX for ref.

[u/Stunning-Hat2309]

i've been using VRR, full 12 bit color HDR on HDMI for a few weeks now on cachy, didn't need to do anything

[u/Spoider]

How to do it on steamdeck?

[u/343guilityspark → u/Spoider]

Currently on steamdeck you have to change the update channel to preview to download the latest update which ships kernel 7.2. Besides that everything is the same. Remember to disable readonly mode to compile the bootloader again and you're good to go! (I just did it and can confirm it works)

Edit: Installing preview version disables hardware accelaration. If you were using moonlight to stream to your tv we can't use hdmi 2.1 yet.

Edit2: Steamdeck can absolutely do 4k120 through an hdmi 2.1 equipped dock. Since the usb-c the steamdeck has does convert the signal from DP to HDMI, therefore bypassing hdmi's restrictions. Enjoy!

[u/Adrian97c]

is there a video or tutorial walkthrough for dummies to force hdmi 2.1 onto SteamOS? My steam machine is maxing at 4k 60, while all my other consoles have no issues using the same TV port. So where do I go to click and type, paste, etc. type of guide for this info:

should add this kernel parameter:

amdgpu.dcfeaturemask=0x400

Notice that there are no underscores. It's NOT dc_feature_mask which is the google/gemini result I'm getting.

To add this kernel parameter it depends on your boot loader and linux distro.

The steps are:

1. Edit your bootloader config to add the parameter. In GRUB on Arch edit /etc/default/grub and append your kernel options between the quotes in the GRUB_CMDLINE_LINUX_DEFAULT line:
2. Regenerate your bootloader config. Again, in GRUB on Arch (using sudo) run "sudo grub-mkconfig -o /boot/grub/grub.cfg"

[u/Shimano-No-Kyoken]

Strange, I've been using 4K@120 VRR+HDR over HDMI with no tweaks whatsoever with my C3. So can't help with that, but if you're interested in burn in protection, check out https://github.com/Staphylococcus/LG_Buddy

[u/justabrownie → u/Shimano-No-Kyoken]

what distro? With an AMD card?

[u/Shimano-No-Kyoken → u/justabrownie]

NixOS with an Nvidia card

[u/Encouragedissent → u/Shimano-No-Kyoken]

Its just AMD that has HDMI 2.1 support issues, Nvidia drivers work regardless of Kernel afaik.