Hi,
I was wondering if a product from the store could solve my issue and when I clicked ask a question it directed me here.
My setup uses a 4k 120hz TV with VRR support, an AV receiver connected with eARC and a Linux Gaming PC with an AMD GPU running Arch with Hyprland as windowmanager and pipewire + wireplumber for audio…
I obviously want to use 120Hz and VRR since those are nice features and make Games feel a lot smoother. Now since you cannot just plugin an HDMI 2.1 cable and call it a day I did what several other people in the freedesktop gitlab issue for AMD HDMI 2.1 did and bought some janky DP 1.4 to HDMI 2.1 adapter that uses some VMM-7100 chip.
(the following paragraph is just background fluff on my setup and what I tried)
Connected to my AV receiver I did not get any sound. I had more important stuff to do but after 200 hours of Last Epoch I now finally wanted to tackel this. Yesterday I sat down and tried getting it to work. I started by connecting to the TV directly and was getting sound that way but after ~10 seconds it dropped for ~1 second. And while 120Hz was working, VRR was not, despite the Amazon product page explicitly claiming that it would support VRR several times. (An Amazon product description for a janky adaper being wrong, I know … totally unheard of 
) So I connected it to my old Windows PC, Sound was working without issues. While on Windows I flashed a firmware from a different adapter on mine and suddenly Windows reported that it found a VRR compatible display. Back on Linux I now was able to get 120 Hz with VRR showing me that it is possible with my current TV and GPU. (There is still some jank e.g. SDDM is now a black screen and in the window manager I got flickering which reconnecting reconnecting of the HDMI cable seemed to solve then starting gamescope resulted in a black screen but setting VRR to only be enabled when an application is in fullscreen seems to have solved that. I started Last Epoch and the TV said “freesync active” and it felt great. However the sound issues were still there. Switching to 5.1 sound I noticed that it now drops audio more frequently like every 1-2 seconds.
Current situation:
Audio over HDMI works fine
Audio over DP - HDMI drops a second in regular intervals where the interval length is determined by the number of channels (info screen on TV shows the PCM icon disappearing during second without sound)
Audio over DP - HDMI seems to work fine on Windows but I only tried stereo (last time I checked I was unable to tell Windows to output 5.1 sound cause it insisted that my TV is a stereo device and the only solution I found back then was to connect it to the AV receiver)
Since it seems to work under Windows I haven’t given up on the Adapter completely yet … So here are my questions:
Does anyone have an idea on what settings I could change?
(I have zero knowledge on how to configure pipewire properly and have never been this confused by config files … ALSA, pipewire and wireplumber all have config files containing the same things and each of them has multiple config files … tbh I wasn’t able to figure out where the actual used config comes from, any changes I tried had no effect and I was only able to switch from stereo to 5.1 after “giving up” and installing pavucontrol)
Is this most likely an bandwith issue (it is only DP1.4 which technically doesn’t have enough bandwidth for what I want if I am not mistaken) or just a crappy adapter issue? But then why is it working under Windows …
Is the EDID Feeder - HDMI 2.1 / DisplayPort 2.0 that I saw on the store (and that sent me here) the best solution for this issue? (from how I understand it it does all I want and by using DP 2.0 it should have enough bandwidth)
Is my adapter just a faulty and buying another of those random VMM-7100 chip adapters has a high chance to solve the issue? (I don’t want to end up with a collection of those things … the one I have did its job in the sense that it proved that it can work so I now am less hesitant of buying something of higher quality)
Potential workarounds I already thought of are:
using the onboard audio but that would be analog and not provide the option to passthrough digital audio that I want my receiver to decode
using an HDMI port of the graphics card for sound but since HDMI requires video it would create a display for applications and my mouse cursor to get lost on.
I don’t like the downsides so these would only work as temporary solutions … and since there is nothing more permanent than a temporary solution I am hesitant to use either of those.
Thanks for reading my rambling, I feel like I wrote it way too unstructured and confusing 
and too much text in general
So if anyone has some ideas on what I could try that would be awesome 
But I am also fine with reassuring words that the EDID Feeder - HDMI 2.1 / DisplayPort 2.0 will work great for my use case and that I will be as super happy with it … Then I’ll buy that and be as happy as someone can be when he spends over 200 bucks (with shipping and customs it will be more like 300 
) to have functionality that could just work without an adapter if the HDMI forum would allow AMD to add support for it to their driver …
edit:
update after further testing:
- With the AV receiver I don’t get VRR enabled. I am kinda sure that VRR over that port worked with the Xbox Series X cause Elden Ring felt smooth to me … but now I am starting to doubt my perception.
- There is no sound but under info it shows the input with the correct speaker setup (switching from stereo to 5.1 is correctly shown on the info screen)
- Opening the setup menu of the receiver suddenly lets it play sound, less choppy than with TV over eARC but still choppy, closing the menu so that the screen is shown again results in no sound again
- connecting to a PC monitor plays stereo sound without issues
This reminds me of my consolized GameBoy Advance, when testing it during assembly with my monitor it works with sound but when sound over HDMI was enabled the TV didn’t even show a picture and leads me to the assumptions that the main issue is that HDMI is a horrible standard 
But that it works on a different monitor and with Windows has me worrying that it is an issue with the signal itself, however sound is fine when connected over HDMI directly 
… so I wonder how likely the EDID Feeder - HDMI 2.1 / DisplayPort 2.0 would solve my issue.