No HDMI 2.1 Support in Linux Problem

I wrote earlier about the HDMI drama around Linux and HDMI 2.1 support.

Long story short, using Bazzite over HDMI to a 4K TV is limited to your TV’s HDMI 2.0 capability. Using a Cable Matters active Display Port -> HDMI 2.1 adaptor will allow a 4K 120Hz, 10-bit color depth, with High Dynamic Range (HDR) but no VRR.

How to Get HDMI 2.1 Support

It is possible to get HDMI 2.1 support in Linux that includes 4k 120HZ, 10-Bit color, HDR, and VRR. It works pretty well with my LG C1 OLED and a Gigabyte Radeon RX 7600 XT 16G, but there are some issues.

Cable Matters Display Port 1.4 -> HDMI 2.1 Adaptor

➡️ This Cable Matters active Display Port 1.4 -> HDMI 2.1 adaptor is the one to get.

If it has the newer firmware installed, you will only get a fixed refresh rate out. You will have to downgrade the firmware to get VRR. It didn’t work well enough for everyone, so Cable Matters removed VRR support.

The steps below are a hack and may not work for your setup. Check the return policy before buying.

Note: This adaptor is for Display Port 1.4. If your GPU is newer and has Display Port 2.1, then this adaptor will not work.

Flash the Old Firmware ⚡️

Cable Matters has provided the old firmware for the adaptor to enable VRR. You have to use their tool and flash the 7.02.120_forVRR firmware.

This is a Windows only tool and requires a full-sized Display Port connected to a working display to flash. It will not work through a dock. (I had to ask a friend to flash mine for me since the whole point of the Bazzite build is to avoid having Windows!)

Make Sure Your Setup Can Do HDMI 2.1

Once the adaptor is ready, double check your setup.

1. A TV capable of HDMI 2.1. Even if your TV can do HDMI 2.1, double check the HDMI port you use is capable. On some TVs not all of them are.
2. An HDMI cable capable of the bandwidth needed. You want an “Ultra High Speed” HDMI 2.1 cable. “High Speed” will not work. Look for the certified badge to be sure.

➡️ This is the HDMI 2.1 cable I used

Once all the pieces are together, hook everything up and se if it works! 🤞

TV Setup

I had to adjust a few things for the picture from the dongle to look good on my LG C1 OLED.

Be sure to enable VRR (AMD FreeSync for my setup).

Game Optimizer -> AMD FreeSync Premium 

This adaptor uses a different color space than the default HDMI out does. You may need to adjust some TV color settings to get things to look right. My picture was too dark, so I had to adjust HDR Tone Mapping.

All Settings -> Picture -> Advanced Settings -> Brightness -> HDR Tone Mapping -> On

I also had overscan with the Display Port adaptor that was cutting off the edges of the picture. You can turn that off in:

All Settings -> Picture -> Aspect Ratio -> Just Scan -> On

Remember This is a Hack

This adaptor seems to work well for me, but it is not without problems. Here are a few I’ve encountered:

• If I toggle HDR in Steam, my TV loses the signal and it won’t get it back unless I force a restart.
• Sometimes after the system wakes from sleep, the dongle no longer has audio. The HDMI/DP audio option in settings is gone. I can’t restore it unless I restart.

Once it’s set up and running, things seem stable for me. Remember, if this adaptor doesn’t work, there is always Windows. It has full HDMI 2.1 support. Good luck!