AMD eGPU with VRR/FreeSync on LG C4 TV
I'm looking to add an eGPU to my Rog Ally X when docked (AOOSTAR AG02 with a 7900XT). I'd like to go AMD since I want to have Game mode and do couch gaming.
The cards I'm looking at support both Display Port and HDMI, but the TV has only 4 HDMI 2.1 ports. It does support VRR/G-SYNC/FreeSync Premium. From my understanding VRR won't work due to HDMI not approving AMD implementation of HDMI 2.1 but that should not matter because we can use AMD FreeSync using HDMI 2.0 at 4k 60Hz from what I can tell. The limitation would be that I cant go above 60Hz at 4K.
Would a DP1.4 to HDMI 2.1 adapter work to achieve both FreeSync and 4K120Hz? Am I missing anything on this setup?
13 Replies
unfortunately the only way is to try it and see
I am able to use VRR just fine (RX 6800), but not some other HDMI 2.1 features - in particular I can't use 4:4:4 display modes. But VRR and HDR seem to work fine. Granted, I can't get games to be as smooth as I can Windows, from in GameScope, which sucks...
(LG OLED C2, btw)
There are times/cases that I have not fully identified that do cause VRR to get disabled. Usually a quick restart will fix it. Also, sometimes the system (GameScope settings) will report a mode that the TV does not report. For example, it'll say I'm running at 4k@120 in system settings, but the TV will say 4k@60. (You can spam the green button on your remote to see what the TV is actually running at). This causes massive choppy frame pacing. Usually just toggling the mode in settings a few times will fix it.
Thanks for the insight, very helpful! I'll give it a try with a HDMI 2.1 cable once everything arrives and if it doesn't work then I'll see if a DP to HDMI might be worth it. If I can't get it to work maybe adding Windows as a second option wouldn't hurt.
Just to clarify: This is because AMD does not support HDMI 2.1 on Linux
A DP to HDMI (active cable) you will kill the VRR signal and with DP++ (passive cable) you get VRR but no HDMI 2.1. There's no perfect solution for TV use.
VRR does work though - it's not as smooth as it is on Windows, and I can't get 4:4:4 modes, but you can at least get VRR to work.
It works (and is enableable) in both Gnome desktop and GameScope mode
But with 4:2:0 you'll only have half the chroma resolution on both vertical and horizontal. Only the brightness information is full resolution. (The only reason why HDR on 4:2:0 can be worth it)
It's a YCbCr mode
Not full RGB
So if you want absolute full detail, that's not the way to go. If you just want HDR for automatic brightness control, then sure, this is just fine. HDR brightness control is nice on its own.
It's 4:2:2, but yeah, that sucks. Subjectively it looks pretty good
Er, actually you are right, it's 420, and the color difference between that and 444 is fairly noticeable. I switch to @60 to try out 444 and see the difference. In my case that's actually fine - the 6800 RX I have doesn't run fast enough anyway, most of the time at 4K (though adding 16GB of system RAM to a total of 32GB may have helped - need to do more testing)
I think I’ll do that as well. I’ll shoot for 4k@60.
Am I right in thinking that the only drawback with AMD and not having HDMI 2.1 is not being able to go beyond 60hz? (So freesync/VRR works and HDR 4:4:4 works on LG C2/4 with HDMI 2.0)
I am able to output 4:4:4 at 4k @60Hz, but not higher - I believe it has to do with greater available bandwidth in HDMI 2.1 - and the fact that we can't access that because of some feature no one wants, needs, or would even use on Linux, is beyond maddening...
Also super irritating that AMD can't just release an implementation that simply skips DRM - there should be a class action lawsuit over this
its HDMI forum gatekeeping AMD
they decided AMD is not allowed to open source their HDMI 2.1 driver
and thus its not included in kernel
Yeah - it's still super irritating
it might still eventually come to linux in form of a blob
aka binary firmware
From what I understand, AMD proposed a solution where the DRM part is a blob - but HDMI being complete piles of garbage, said no - and AMD rolled over.
I don't even want the DRM - everyone involved can take that blob and stuff it where the sun don't shine. I really don't care. I just want the hardware I bought to work.