4K @120Hz over HDMI on AMD GPUs?
Hello, after getting my Steam Deck and loving it I want to build a home theatre PC that runs Bazzite. I'd be looking at a high-end AMD graphics card (not decided yet) to play on my 4K 120Hz TV. However, I've seen that AMD GPUs don't support HDMI 2.1 on Linux, but I've seen you can get some DisplayPort adapters to fix this. Has anyone used any of these adapters successfully? And is it possible to have VRR support when running 4K 120Hz? I also have a reference model 7900XT which has a USB-C port as an output. Would it be possible to use that GPU and use a USB-C adapter instead?
I don't use Linux outside of my Steam Deck, so any help is appreciated. 🙂
48 Replies
Hey there. I've got my 4k 120hz TV properly working with one of these adapters. Works as you'd expect. You can see reports of people using this adapter here
GitLab
4k@120hz unavailable via HDMI 2.1 (#1417) · Issues · drm / amd · Gi...
Brief summary of the problem: I have a RX 6800 XT connected to a LG B9 TV via HDMI. As both...
Oh that's awesome. Did you have to flash a new firmware to get VRR working? Or does it work out of the box?
Nope, worked OOTB
I have an LG C2, 7900 XTX GPU and a CableMatters HDMI 2.1 to DP 1.4 adapter.
It's definitely not the greatest experience:
1. When the system goes to sleep, the TV doesn't know to shut off anymore
2. Sometimes when booting, certain screens don't show up (like the LUKS drive encryption password prompt)
3. HDR requires toggling on and off a lot in Plasma until the TV switches to HDR mode
4. Sometimes the screen glitches and it goes to a black screen in fullscreen applications, exiting fullscreen and re-entering fixes this
5. Potentially worse VRR stability? I'd have to test, but I feel like the TV's refresh rate doesn't follow the game's FPS as well anymore, but it could be placebo.
6. Not a real issue, but since it's DP 1.4, this means DSC has to be used as DP 1.4 does not natively have enough bandwidth for 4k 120hz, I believe. Still worth mentioning.
I haven't had any of these issues when using the HDMI cable. But of course, the screen looks awful because of not having HDMI 2.1 support.
I still think these issues are worth it in order to get proper colors and such, but they definitely are annoying.
I find most of the issues regarding display adapters are moot when using Steam game mode in a HTPC setup, which is what the OP is trying to do
I use the adapter in Steam game mode exclusively with no real issues
Definitely good caveats to note though for desktop use
Thank you so much to both of you for the help, so useful 😄. I think I will go for the CableMatters adapter as it’s easier for me to buy.
@RTK | PrussianPrince did you have to update the firmware on the CableMatters adapter to get it to work?
No. It worked out of the box, VRR included.
Technically it says the adapter doesn't support VRR, I believe, but it works for me and others have reported the same, so...
Right, I suppose they don’t want to deal with testing and RMA for VRR 😅. I’ll order one of the CableMatters adapters then to test it. Thanks for the help!
No problem, hope it works out well for you 😄
Glad to help! That adapter should work well too
Hmm @Geechan @RTK | PrussianPrince I’ve installed bazzite to test on my current PC (7900xt) and when plugging it via HDMI (no adapter) into my 4K 120Hz tv, it seems to recognise 4K @120Hz and can run it just fine with VRR working perfectly too. I thought that was impossible, but to my eyes it’s definitely running higher than 60 and VRR is definitely working. The TV also reports that it’s recieving a signal at 4K 120Hz with HDR and shows the correct VRR framerate. It’s a little janky sometimes but it seems to be managing it without an adapter. Is this normal?
When waking the PC the signal will cut out when using VRR and I have to restart the TV to reconnect and when changing resolutions there’s some audio garbling but it does seem to be able to run 4K 120Hz with HDR and VRR somewhat consistently?
Potentially the TV doesn’t seem to recognise that it’s HDMI 2.0 and just allows it to run 2.1 features? I’m not sure how this works, so I’m probably wrong.
You can get 4k 120hz, HDR and VRR without an adapter, yes. That's not the problem.
The problem is colors will be off.
For starters you will be stuck on 8 bit, and chroma subsampling 4:2:0 vs 4:4:4
I don't pretend to understand what that is, but if you can't notice it that's fine.
I can though.
I really don't believe the adapter is working properly regardless of firmware version.
I've tried multiple firmware versions and each of them has a problem.
VRR activates but does NOT work properly
The only solution working for me is HDMI 2.0 (4K120 @ YCbCr 4:2:0)
To be fair I can’t notice 😅 but after further testing I can’t seem to get VRR to hold properly. It works perfectly but when I put the PC to sleep and wake again VRR will refuse to activate saying the display doesn’t support it and I have to restart the whole PC to run VRR. So when it’s on, to me it’s perfect. But it seems to stop working pretty often.
Hmm that’s a shame, to me VRR is a must-have. I’ll still buy an adapter to see what I can get working on my end.
It's really disappointing. HDR/VRR seems to be a complete mess on Linux.
To be fair, HDR on Windows is also a mess but at least VRR and HDMI 2.1 works
It’s odd because I’ve just seen it work perfectly without an adapter but the image just dies occasionally and when waking from sleep.
I haven't tested sleep/wake but I probably should 🙂
Ahh, yep. sleep/resume is causing it to completely freak out.
Looks like disabling/enabling VRR after it resumes works
Yeah I wonder if this is a bazzite issue rather than general Linux or if it happens on other OSs?
I think it's driver-related ... HDMI forum won't allow AMD to use HDMI 2.1 under Linux (and open source)
Yeah I suppose, just seems so fixable (thanks HDMI forum …)
Is that on your TV or through the performance window? I assume this is without an adapter? Also when I load up from power off with VRR on when I connect my controller, HDR turns on and off like 5 times before settling down and working fine, very strange.
I'm not really sure what you mean by that. The refresh rate of the TV I use definitely changes with the adapter, when VRR is on.
My only suspicion at the moment is that it's not as "stable" as the native HDMI connection (as in, it fluctuates more), but this could also be placebo.
I haven't really checked what happens on sleep though.
I made the computer sleep and then resumed (using wake on lan). After resuming I had to disable/re-enable VRR
Does gamescope framerate match your TV? (if you have an LG you can see it in the hidden menu)
Mine was not even close. It keeps jumping between 60 and 120 when gamescope was saying 74 fps solid.
Yeah, I have an LG C2. What hidden menu are you talking about? The one that shows the resolution/refresh rate/bits/whatever? If so, yes, that's what I've been following, and comparing with the game one.
I don't really use gamescope unless I play something in HDR.
Which is not very often at the moment so I'm not 100% sure what the behavior there is. But in regular games, it definitely does not jump between 60 and 120 as you say.
Yeah, I was using gamescope for everything so that might be the problem
I didn't check behavior in KDE (or Gnome/whatever)
There used to be an issue where moving the cursor forced the refresh rate to max, on KDE. I didn't have that with GNOME.
I used to have that issue too, but I don't have it anymore (I think it was related to using hardware vs software cursors or something of the sort).
But with a controller that shouldn't be a thing.
@Geechan are you able to do 4k120 in game mode? How about with HDR?
Yes, that all works for me. HDR and VRR also work with the adapter I brought. In fact, I only use it in game mode
I ordered mine today. Hopefully it works well. What's your GPU?
Everything works almost flawless for me with the cable matters adapter and a LG C2 ,except the singal is unstable and I sometimes get stuck on an invalid signal error. I have to restart the tv to fix it. Luckly I have ssh accses to my tv so I can reboot it with one command on my phone or PC but it is still anyoning.
It especialy happens with HDR. It's almost impossible for me to get a stable signal with hdr.
Once I get a working signal it will work until I power off /sleep the pc or tv so at least it's not going out in the middle of the game
not sure if this because I am running a really long HDMI cable I think 20ft so that could be part of the issue.
IIRC HDR requires about 2x the bandwidth so could be the long cable or the adapter (this is based on using HDR with gpu passthrough which doubles the bandwidth needed for looking-glass, so might not be the same)
FWIW this worked out of the box using an HDMI cable for me on an AMD 7900 XTX with a few caveats:
- Fixed resolution (4K@120), VRR disabled and HDR enabled causes flashing.
- Fixed resolution, VRR enabled and HDR enabled is fine out of the box.
No clue why. This is feeding into a Samsung Frame if that makes any difference.
No yeah you can do 4k120 VRR and HDR on HDMI 2.0b
so you don't need HDMI2.1 support or a adapter
but it won't be a full rgb signal it will be a commpresed YCbCR signal.
so I can connect my LG C2 to my 6700xt with just a HDMI cable but i will lose color accuracy.
the only problem with the adapter is the random invalid signal error, but like I said I can just ssh from my phone or something and reboot my tv to fix it
its rare though unless i use HDR (then its almost guaranteed it will fail) prob because of the higher bandwith and the really long cable legnth
I have the CableMatters adapter but can't get 4k120 in game mode.
So I'm going to try the AliExpress one.
This one?
https://www.amazon.com/gp/product/B08XFSLWQF
that's the one I am currently using with my LG C2 and my 6700XT
only thing is I somtimes have to reboot the tv like I mentioned to get a signal.
Cable Matters 8K DisplayPort 1.4 to HDMI 2.1 Adapter with 4K 120Hz ...
8K Flexibility Across Standards Bridge the gap between 8K DisplayPort and HDMI with the Cable Matters 8K DisplayPort to HDMI Adapter. Effortlessly convert a DisplayPort port on a gaming PC or multimedia system to an HDMI connector for a television or monitor. Maintain support for the latest HDMI ...
I've also used this one https://www.Amazon.Com/gp/product/B0B2933L7T but it died on me after a while and it's no longer available.
8K@60Hz DisplayPort to HDMI Adapter, Uni-Directional DP 1.4a to HDM...
8K@60Hz DisplayPort to HDMI Adapter, Uni-Directional DP 1.4a to HDMI 2.1 Converter Cable, Support 8K, 4K@120Hz, 2K@240Hz, VRR, HDR, HDCP 2.3, DSC 1.2a for HP, ASUS, DELL, GPU, AMD, NVIDIA
Intrestingly the second one mentions to only use HDMI cables shorter than 10FT while the first one doesn't specify that. mine is like 20 i think :clueless:
This is the one I'm currently using:
Cable Matters 8K DisplayPort 1.4 to HDMI Cable 6ft / 1.8m with 4K 1...
With 8K flexibility for all standards Connect the gap between the DisplayPort (8K) and HDMI to HDMI 2.1 (8K) with the Cable Matters Cable for DisplayPort1.4. Easily connect an HDMI TV or monitor to the DisplayPort port of a desktop PC. Continuous support for the latest HDMI standards including 4K...
Ah your using the one that has a built in cable. It should be more or less the same I think as the one I used except it comes with a cable on the other end. Mine you need to plug in ur own hdmi cable into the adapter.
i got it like that so i could run a longer cable
I ended up swapping to an adapter. I don’t get VRR, but 120@4K + HDR is working much better.
Without the adapter, I was able to enable 120 @ 4K with HDR and VRR…. But there was something wrong with the signal. Disabling VRR had the image flashing. With VRR, there was a slight “pulse” effect. A net improvement, but a reminder that the drivers aren’t perfect (this time due to legal nonsense with the HDMI forum, not technical issues. This is unlike the 5K / 8K display support).
I’m using this adapter: https://a.co/d/dfCIxTb
With a 25 foot cable, since there was some concern around cable length earlier in the thread.
Cable Matters 8K DisplayPort 1.4 to HDMI 2.1 Adapter with 4K 120Hz ...
8K Flexibility Across Standards Bridge the gap between 8K DisplayPort and HDMI with the Cable Matters 8K DisplayPort to HDMI Adapter. Effortlessly convert a DisplayPort port on a gaming PC or multimedia system to an HDMI connector for a television or monitor. Maintain support for the latest HDMI ...
Bit late, but I have it connected to a 7900 XTX
not sure why, but on my Sony X90L HDMI 4k@120hz just works when directly plugged in on the 7900XTX, it just doesn't do VRR
I have had no luck with any of the recommended displayport adapters, these seem to work on TVs like LG that say they support freesync out of the box, and not TVs like Sony which advertise HDMI-forum VRR
like it was said above you don't need a display port adapter to do 4k@120hz even with VRR and HDR. what you DO need a displayport adapter for is 4k@120 (with or without VRR and HDR) at full RGB
hdmi 2.0b (HDMI 2.1 gets downgraded to 2.0b without the propirtary 2.1 support) only has enough bandwith for 4k@120 YCbCR 4:2:2 chroma sub sampling (with or without VRR and HDR)
basicly that means the colors are compressed at 4k@120 unless you have displayport bandwith (through an DP 1.4 adapter and even then I think its still a DSC signal so its still compressed) OR propitary HDMI 2.1 bandwith (which does have enough bandwith for a completly uncrompressed 4k120 RGB signal)
TLDR
theortically you dont need any extra hardware for 4k@120 freesync (HDMI VRR is not the same as the older freesync and does recquire HDMI 2.1 also HDMI 2.1 does not imply the older freesync) and HDR over HDMI it should work ootb right now on linux but with compressed colors
dp 1.4 adapter does NOT have the same bandwith as HDMI 2.1 and can only achive 4k@120 through a DSC signal (DSC is supposedly lossless i think)
Got my adapter! It seems to work! Thanks!
Glad to hear!
does it work on reboots? mine works but only boots once, if i reboot and on subsequent coldboots i get a black screen
Did not have this issue, but when I initially changed resolutions in gaming mode I only saw a blank screen. I unplugged my cable and plugged it back in and then all was good.