When Valve announced its upcoming Steam Machine hardware last month, some gamers may have been surprised to see that the official spec sheet lists support for HDMI 2.0 output instead of the updated, higher-bandwidth HDMI 2.1 standard introduced in 2017. Now, Valve tells Ars that, while the hardware does indeed support HDMI 2.1, the company is struggling to deliver full support for that standard due to Linux drivers that are “still a work in progress on the software side.”
As we noted last year, the HDMI Forum (which manages the official specifications for the HDMI standards) has officially blocked any open source implementations of HDMI 2.1. This means that the open source AMD drivers used by SteamOS may not fully implement some features that are specific to the updated output standard.
“An open source HDMI 2.1 implementation is not possible at this time without violating HDMI Forum requirements,” AMD engineer Alex Deuchter said at the time.
They are doing what they can
This situation has caused significant headaches for Valve, which tells Ars it has had to validate the Steam Machine’s HDMI 2.1 hardware through Windows during testing. And when it comes to HDMI performance through SteamOS, a Valve representative tells Ars that “we’re working on trying to unblock things there.”
This includes unblocking the resolution and frame-rate limits of HDMI 2.0, which is a maximum of 60Hz for 4K output as per the official standard. Valve tells Ars that it’s able to push that limit up to “4K @ 120Hz” listed on the Steam Machine spec sheet, however, thanks to a technology called chroma sub-sampling.
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