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Guide: how to get HDMI 4K120 to work with Intel GPUs

edechamps
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Note: I originally posted this guide with proper links throughout. However that caused my post to be automatically marked as spam. As instructed, I tried to report my post to a moderator, but nothing happened despite trying again every day for a week. Therefore I am reposting this with links mangled in an attempt to get through the automatic antispam filter. Thanks, Intel.

Are you trying to get your Intel Xe GPU to output 4K (3840x2160) at 120 Hz RGB 4:4:4 to an HDMI display? If so, read on.

TL;DR: use this Cable Matters adapter[1] or this Satechi USB4 docking station[2] and make sure to update their firmware using this tool[3] (it's from Cable Matters but will work with the Satechi too). Other adapters are unlikely to work unless the manufacturer explicitly states that they support 4K120 with Intel 11th gen GPUs.

I just completed a long series of experiments and concluded that while outputting 4K120 to HDMI from an Intel GPU is indeed possible, due to various compatibility issues it requires very specific combinations of hardware that can be very tricky to get right. I spent a lot of time trying to make this work, and am writing this guide so that you don't have to.

Obviously, I'm going to assume that you have an HDMI 2.1-enabled display capable of 4K120 RGB 4:4:4. For example a LG G1 OLED TV which is what I use.

First of all, unless your case is atypical, you can't use the HDMI port on your computer to output 4K120. This is because Intel dropped the ball and decided to only provide an HDMI 2.0 port, but you need HDMI 2.1 for 4K120. Thanks Intel.

Fortunately, there is a way around this problem. DisplayPort over Thunderbolt 4 supports up to 40 Gbit/s of display bandwidth. So, assuming your computer has a Thunderbolt 4 port, we should be able to convert that to HDMI 2.1, right?

In theory yes. In practice, if you just try a random Thunderbolt 4 to HDMI 2.1 adapter, you'll find that it doesn't quite work properly. You will likely run into one of two issues:

  • Certain devices, such as this Cable Matters adapter[1] and this Satechi USB4 docking station[2] (note USB4 is basically a subset of Thunderbolt 4), have a firmware bug that prevents them from going above 1080p with Intel 11th Gen CPUs.
  • Other devices, such as this Lenovo dock[4] and this Sabrent adapter[5], have a different problem whose symptoms depend on your Intel GPU driver version:
    • If you try to use them with Intel GPU driver 30.0.101.1692, you will in fact get a picture in 4K120 RGB, but it is not stable - you will get random black screen flickers (which were already reported elsewhere[6]).
    • If you try to use them with Intel GPU driver 30.0.101.3111 or 30.0.101.3222, the GPU will output YCbCr420, not RGB 4:4:4, as soon as you try to go above 4K60. There is no way to force it to output RGB.
    • I have reported my findings to Lenovo[7] but they have yet to acknowledge the problem.

From the above you'd be tempted to think that the limitation is on the PC side and there's no way to get 4K120 to work. You'd be wrong. There is a way to make it work, but you need to use just the right adapter with just the right firmware.

Turns out that Cable Matters is a winner here, because they correctly identified the problem[8] and released a firmware update[3] to fix it. So one solution is to buy the Cable Matters adapter[1] I mentioned above - just make sure to update the firmware! With that approach, you should be able to select 3840x2160 at 120 Hz and it should work flawlessly in RGB 4:4:4. You can even go to 10-bit and enable HDR! (The only thing that doesn't work is Variable Refresh Rate (VRR) but I believe that is "normal".)

So, is Cable Matters the only game in town? Actually no. Other manufacturers might also provide adapters with working firmware, though I'm not aware of any. However, interestingly, some adapters use the same chip as the Cable Matters adapter and can be flashed with the same the firmware update tool that Cable Matters provides! Notably this is the case of the Satechi USB4 docking station[2] which can be made to work this way (but not the Sabrent nor the Lenovo dock).

Note that it is also possible to use a standard Thunderbolt 4 docking station and chain an adapter such as the Cable Matters adapter into one of its downstream TB4 ports - I have verified that it does work.

So there you have it. To conclude, and at the risk of stating the obvious, I'll just remind you that, if the adapter you use doesn't come with an HDMI cable, you need to make sure to use one that is HDMI 2.1 capable. Look for a Ultra High Speed certification[9].

Hope this helps!

Additional information

Experiments were carried out with the following hardware:

  • Host PC: Lenovo ThinkPad X1 Yoga Gen 6 (with latest firmware)
  • GPU: Intel® Core™ i7-1185G7 Processor (Intel® Iris® Xe Graphics)
  • OS: Windows 11 21H2 22000.832, fresh install. Also tried on Windows 10, same behaviour.
  • Display: LG G1 OLED TV (HDMI 2.1)
  • HDMI Cable: Stouchi HDMI 2.1 cable

Links (this forum antispam filter forced me to mangle them):

[1]: amazon.co.uk/Cable-Matters-48Gbps-Adapter-Supporting/dp/B08MSWMXT4
[2]: satechi.net/products/usb4-multiport-adapter-with-8k-hdmi
[3]: kb.cablematters.com/index.php?View=entry&EntryID=147
[4]: lenovo.com/gb/en/accessories-and-monitors/docking/thunderbolt-docks-universal-cable-docks/TP-TBT-4-Dock-UK/p/40B00135UK
[5]: sabrent.com/products/da-uch8
[6]: community.intel.com/t5/Graphics/Random-black-screen-4k120-Intel-Iris-Xe/m-p/1352070
[7]: forums.lenovo.com/t5/Displays-Options-and-Accessories/Please-update-the-firmware-of-Thunderbolt-4-Universal-dock-to-support-4K120-with-Intel-GPUs/m-p/5162817
[8]: kb.cablematters.com/index.php?View=entry&EntryID=136
[9]: hdmi.org/spec21sub/ultrahighspeedcable

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