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The HDMI Forum rejected AMD's open source HDMI 2.1 implementation

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If you were hoping at some point to see HDMI 2.1+ on Linux with AMD + Mesa, you're out of luck right now as it's simply not going to be happening.

There's been a bug report on the Mesa GitLab of "4k@120hz unavailable via HDMI 2.1" that's been open for a few years now, with lots of comments and chatter about the issue. The problem is that HDMI is a proprietary interface, whereas DisplayPort is run by the international non-profit VESA, so it's much more complicated for HDMI support.

In an update on the bug report, AMD engineer Alex Deucher commented: "The HDMI Forum has rejected our proposal unfortunately.  At this time an open source HDMI 2.1 implementation is not possible without running afoul of the HDMI Forum requirements."

So if you're on Linux, it's going to continue to be best to buy hardware that uses DisplayPort.

On the NVIDIA side though, it seems like it may not be an issue, as developer Karol Herbst wrote on Mastodon: "Even though AMD might not be able to add support for HDMI 2.1, nouveau certainly will as Nvidia's open source driver _also_ supports HDMI 2.1 so there is no reason to believe that at least some drivers can't support HDMI 2.1

It's quite backwards, but apparently having all the logic inside firmware (like Nvidia does) will probably help us implementing support for HDMI 2.1"

So perhaps in future AMD may be able to do something similar with their firmware.

Article taken from GamingOnLinux.com.
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maddovr Mar 1
Quoting: TheRiddick
Quoting: maddovrAre you sure you're getting 10-bit and 4:4:4 subsampling?

I don't have the card. I just checked under WAYLAND when I did and the display information app which I've forgotten the name of, said 10-bit colorspace!
Check your output information and paste them to see if there is any subsampling going on or not, it varies between compositors so I can't provide any command unless I know what yours is, but this is still very strange.
pete910 Mar 1
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Thing is, If all the major TV maufacures + AV OEMs turned round and said "From next year all equipment will drop HDMI in favour of Display port" the HDMI license ect would all of a sudden become next to nothing if not free!
F.Ultra Mar 1
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Quoting: maddovr
Quoting: F.UltraSave your money, you have no legal standing and your case would be thrown out of court.
There could possibly be a case against AMD however. I'm not in the legal field of studies, but AMD is advertising HDMI 2.1 on their RX 6000 and 7000 cards even on linux when that is not the case. So maybe...

AFAIK their closed drivers supports HDMI2.1

Quoting: pete910Thing is, If all the major TV maufacures + AV OEMs turned round and said "From next year all equipment will drop HDMI in favour of Display port" the HDMI license ect would all of a sudden become next to nothing if not free!

Small problem here is that it is the major TV manufacturers that make up the HDMI consortium, that is also why HDMI is on every TV while DP isn't.

Founding members of HDMI:

Hitachi, Ltd.
Panasonic Corporation
Sanyo Electric Co., Ltd.
Panasonic Corporation
Philips Electronics N.V.
Silicon Image, Inc.
Sony Corporation
Technicolor S.A. (formerly known as Thomson)
Toshiba Corporation


Last edited by F.Ultra on 1 March 2024 at 5:09 pm UTC
Quoting: F.Ultra
Quoting: maddovr
Quoting: F.UltraSave your money, you have no legal standing and your case would be thrown out of court.
There could possibly be a case against AMD however. I'm not in the legal field of studies, but AMD is advertising HDMI 2.1 on their RX 6000 and 7000 cards even on linux when that is not the case. So maybe...

AFAIK their closed drivers supports HDMI2.1

Quoting: pete910Thing is, If all the major TV maufacures + AV OEMs turned round and said "From next year all equipment will drop HDMI in favour of Display port" the HDMI license ect would all of a sudden become next to nothing if not free!

Small problem here is that it is the major TV manufacturers that make up the HDMI consortium, that is also why HDMI is on every TV while DP isn't.

Founding members of HDMI:

Hitachi, Ltd.
Panasonic Corporation
Sanyo Electric Co., Ltd.
Panasonic Corporation
Philips Electronics N.V.
Silicon Image, Inc.
Sony Corporation
Technicolor S.A. (formerly known as Thomson)
Toshiba Corporation
Which makes me wonder. Don't all their set-top boxes and smart TVs and stuff run Linux? So why fuck us around?
F.Ultra Mar 1
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Quoting: Purple Library Guy
Quoting: F.Ultra
Quoting: maddovr
Quoting: F.UltraSave your money, you have no legal standing and your case would be thrown out of court.
There could possibly be a case against AMD however. I'm not in the legal field of studies, but AMD is advertising HDMI 2.1 on their RX 6000 and 7000 cards even on linux when that is not the case. So maybe...

AFAIK their closed drivers supports HDMI2.1

Quoting: pete910Thing is, If all the major TV maufacures + AV OEMs turned round and said "From next year all equipment will drop HDMI in favour of Display port" the HDMI license ect would all of a sudden become next to nothing if not free!

Small problem here is that it is the major TV manufacturers that make up the HDMI consortium, that is also why HDMI is on every TV while DP isn't.

Founding members of HDMI:

Hitachi, Ltd.
Panasonic Corporation
Sanyo Electric Co., Ltd.
Panasonic Corporation
Philips Electronics N.V.
Silicon Image, Inc.
Sony Corporation
Technicolor S.A. (formerly known as Thomson)
Toshiba Corporation
Which makes me wonder. Don't all their set-top boxes and smart TVs and stuff run Linux? So why fuck us around?

Because they don't want the specs to be open, they have zero problems with AMD putting HDMI2.1 support in their closed drivers. Apparently the entire spec is behind severe NDA.
Quoting: maddovr
Quoting: alka.setzerI think, and may be wrong, that this only applies to the open source AMD stack, the closed source driver may not be subject to this limitation.
It does, unfortunately. Both mesa (gpu open drivers including amd's) and AMDGPU-PRO (amd's proprietary drivers) rely on the open source AMDGPU (part of the linux kernel), and this implementation was part of the kernel driver (and can't be anywhere but the kernel). So the HDMI forum rejecting this basically closed off hdmi 2.1 on amd for at least the existing gpus. It may yet be possible for next gpus to support hdmi 2.1 on linux by relying on a firmware level driver (like nvidia does) or on an internal chip that converts displayport signal to hdmi signal (like intel does).

Thank you for the insight. VRR on HDMI is an optional feature in any case. Though freesync/adaptivesync over hdmi is still possible with older versions of the spec. I have an Asus ProArt screen that according to the spec sheet is hdmi 1.4 but does support freesync/adaptivesync (and its working). It's only a 1920x1200, 75Hz display but it works. For people that want higher resolutions, refresh rates and bit rates without compression I guess it would not cut it. In any case for me one advantage of hdmi over display port is that audio always works.
maddovr Mar 2
Quoting: F.UltraAFAIK their closed drivers supports HDMI2.1
They don't, you can see my post above about it. They can't since even their proprietary drivers are based on the open AMDGPU in the kernel.
F.Ultra Mar 2
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Quoting: maddovr
Quoting: F.UltraAFAIK their closed drivers supports HDMI2.1
They don't, you can see my post above about it. They can't since even their proprietary drivers are based on the open AMDGPU in the kernel.

ok, that makes sense. Never used their closed drivers so thought that they perhaps also included a closed kernel module, but that was probably only back in their catalyst days.
pilk Mar 2
Well, making a note that when I finally upgrade this old 1080p60 monitor, I'll have to make completely sure it's one that uses DisplayPort.
Right now, I'm still rocking DVI like it's 2009 (through a DisplayPort to DVI adapter, though.)
Forge Mar 3
Quoting: TheRiddick
Quoting: maddovrAre you sure you're getting 10-bit and 4:4:4 subsampling?

I don't have the card. I just checked under WAYLAND when I did and the display information app which I've forgotten the name of, said 10-bit colorspace!

I have a 7900XTX and a 4K/144Hz panel on my wall. Under Windows, it runs 4K, 144Hz, 4:4:4, freesync and HDR. Under Arch Linux with newest Mesa (24.0.2), it maxes out at 4K, 120Hz, 4:2:0 color and sorta-not-really-HDR (the 4:2:0 subsampling and DSC make it look pretty terrible). I'm in the Github discussion, and it looks like AMD won't be able to do anything.

Just bought *another* 7900XTX to work around my issues, since I have two high res displays that need DP to work right under Linux, plus a DP-only HMD (Valve Index). Hopefully the new card with 3DP+1HDMI will get me working, and I'll be able to find a buyer for a slightly used 7900 XTX Nitro+ (2DP+2HDMI) without taking a major bath on cost.
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