So I have been disappointed that in order to get 4K/120/VRR HDR running on Bazzite (and presumably any Linux distro) the chroma has to be set to 420, which is still OK, but there is very noticeable color banding in skys in games and it can look pretty bad at times.
Most people are aware that the hold up is the HDMI Forum is preventing full bandwidth 2.1 presumably due to the open source nature of the drives, which I do not understand and is a crime if you ask me. Apparently the HDMI forum belives open source drivers pose some sort of security riskā¦I dont know and dont get it.
However, this cable DP1.4 to HDMI 2.1 cable with a custom firmware will supposedly work on some setups. It clearly hasnāt been widely tested, but some users in reddit forums have reported it working.
My interest is solely on using my 9070XT Bazzite in Gamescope.
One thing that I am slightly optimistic about is that if this cable doesnāt work, I have slight hope I can use a future DP2.1 to HDMI 2.1 cable since it wonāt involve any form of DSC, while it may or may not work, but I see it as one less bit of processing it has to do.
Avoid HDMI only displays, it really not worth the headache. I regret i t also , but I dont have a choice.
There are no sanely priced 4k 120+hz oled displays, so stupid tv it is for me.
DP2.1 ā HDMI 2.1 is no easy task requiring specialized and performance active translation, so it will be either extremely expensive pro solution or unreliable consumer shit.
Display matters products are generally the best there is.
Unfortunately my LG C1 doesnāt give me any choice in the matter. Its HDMI or nothing. I have this PC for my living room so I can sit on my couch and play games, going to a monitor/desktop setup completely defeats the purpose as a I already have a 4090 gaming rig in my room.
Semi-relevant, but I use a CableMatters usb-c to HDMI 2.1 adapter to get 4k 120Hz 4:4:4 from my AMD iGPU in linux. Works quite well, but indeed no VRRā¦ I think this has to do with VRR working differently on DP and HDMI but not too sure. These use the VMM7100 chipset, which is the best one for DP->HDMI conversion as far as Iām aware. The advantage of the usb version is that the firmware is still flashable, and CableMatters does offer updates when relevant, and e.g. also a special firmware to expose 120Hz 4k on macs. That doesnāt help with a 7900XTX of course, but interesting nonetheless and it speaks for CableMatters IMO. I tried many adapters before finally landing on this.
I have no 10 bit though, not sure what the limitation there is. Perhaps that would only work with HDR, or itās an AMD driver thing. HDMI from my nvidia GPU can do 10 and even 12 bit on the same setup otherwise.
I wish AMD would just shift the relevant code to the firmware so we could have modern HDMI on linuxā¦
Okā¦well I received my cable and installed the custom firmware and I get VRR HDR and according to the readout from my C1 I am getting the full 10-but chroma subsampling.
Sounds great, right?
However, I am still getting banding in skys in game and I am wondering if maybe there is some setting that isnāt fixing it.
It works on nvidia (also on the open drivers), so I assume the ālicencedā HDMI code on the nvidia side is part of the firmware blob. I donāt know if there is something different about the amd architecture to prevent that, but at least in principle it seems possible.
Intel has support too:
So while HDMI forum seems to suck, 2 other manufacturers have a solution/workaround, and I find it disappointing AMD doesnāt have a solution even on the 9070XT. Thereās still some hope it can be fixed in software later on?
Extreme banding might be using a extremely high compression ratio for Display Stream Compression (because thatās how you get around using full FRL link speeds)
Iām not sure if you can tell the display which compression ratio to use unfortunately.
Generally with no name brands, there are no true UHBR20 to 48Gbps converters, only regular 32Gbps DP 1.4 to 24Gbps TMDS converters.
Cablematters isnāt a no name brand and I do agree that DP2.1 to HDMI 2.1 would likely yield better results since DSC is one less thing the cable has to account forā¦
Howeverā¦it appears this isnāt related to HDMI/DP or anything, but a glitch in Bazzite:
āThe banding seems to go away when the developer setting āDisable Color Managementā is enabled, which makes SDR content appear extremely dark, but makes HDR content look correct.ā
I tried this and all the banding in every game completely went away, which made me happy, but it made Gamescope look very bad so I had to toggle it off when it Gamescope and it certain other games and it made other games look horrible. I am also confused because that link said the issue was fixed.
The TV reading still showed RGB 10FRL with full VRR.
I will probably hook the HDMI cable back up and see how those areas look eventhough I will be back to being limited to 420. If I am not bothered by how it looks then I may just stick to the HDMI cable, return the DP-to-HDMI and get my money back.
Bottom line: If you crave 4K/120 w/VRR 10-bit 444 RGB then this cable with the custom firmware installed has so far been a MASSIVE success. No dropouts. I plugged it in and everything just worked like it was a full bandwidth HDMI cable.
Huh, so this could work if we just source the chip and flashed the firmware ourselves, and used a female HDMI port. This can absolutely be a L1 store product
I personally would add a USB-C for firmware flashing and supplemental USB power to the adapter. I would not solely rely on DP port power, in fact, I would require a USB power source to power the adapter.
I donāt think so. Thereās nothing in that thread that specifically mentions this working with an DP-to-HDMI active adapter in play. Sounds like they are referring to a straight through HDMI cable. Also CalDigit and Cable Matters are among the two best companies making these adapters, IMO. So you arenāt dealing with cheap junk.
Those adapters to my understanding all have ICs that convert the signal from DP to HDMI. Once you try and throw VRR in the mix that ups the complexity probably too much. So i doubt youāll ever see an active adapter any time soon that actually supports VRR. Even then youād probably end up with serious latency issues if you tried.
If you want VRR at the very least you need to stick with pure DP or pure HDMI. As for trying it with USB-C: Iām pretty sure USB-C alternative mode HDMI support was basically abandoned as it hasnāt been update since HDMI 1.4b (also probably why you see many USB-C to HDMI adapters maxing out at 4k@30hz). Best I can tell is the adapters that support anything greater actually incorporate an active DP to HDMI adapter. Then you run into the same issues again with VRR.
It was working wonders yesterday and truly seemed like a miracle solution.
This morning when I turned on the computer it wouldnāt work. It would default to 12-bit at 4K/60 and I could not get it back to 4K/120 444 HDR/VRR like I had it yesterday. Maybe there was a command console to force it, but I couldnāt figure it out.
So I gave up and went back to regular old HDMI with 4K/120 HDR/VRR and 420 chroma. That works well enough and while I can see color banding if I am really looking for it, sitting my couch and gaming makes it almost a non-issueā¦Almost.
I returned the cable. It was fun while it lasted, but I was sensing that this would be something that I was constantly having to troubleshoot and I built this Bazzite gaming PC to have fun and relax.
Normally, if something works and you donāt change the configuration, it works until something breaks, or in the case of your cable, if the signal quality is just at the limit, then it might work sometimes and sometimes not.
But if youāre sure you had 120Hz, VRR, and 444, then Iāll try it with that cable.
I would be happy with 100Hz VRR and 444 and for older games I donāt need Freesync/VRR because I use Radeon Chill anyway.
Edit: e.g HDR, I virtualized libreelec with VFIO on my system some time ago and with it the HDR logo of my LGC1 is displayed briefly when I start an HDR movie, this does not happen with CachyOS or Kubuntu, but I have to take a closer look at it.
Like I said, I am done with it for the time being. I just want to have fun with my living room gaming PC.
The good news is that we now know that it CAN be done and hopefully a little more effort will be put in to make a more permanent solution and other companies (with AMDs support) can make far more reliable cables.
The 9070XT supports DP 2.1 at (I believe) UHBR 13.5, which comes out to 54 GBps total bandwidth, which obviously isnāt the full 80GBps spec. I donāt know if that is 100% true or not, but either way that should make it such that the DP to HDMI conversion wont require any form of DSC. I am no expert, but I would guess that eliminating DSC could make for a much smoother conversion and potentially eliminate any issues.
That is totally a guess, but having one less thing to account for (DSC) can only be a good thing.
Of courseā¦all of this would be irrelevant if HDMI Forum would quit screwing Linux users over.
