DP-HDMI2.1 Protocol Converter Support Being Tackled For Intel Linux Graphics
This DP-HDMI2.1 PCON is protocol converter support as part of the VESA DisplayPort 2.0 specification for interfacing with HDMI 2.1 displays. This protocol converter support for DisplayPort to HDMI 2.1 is necessary even for use with converter chips like the Realtek RTD2173. With these tentative Linux kernel patches, the Intel graphics driver developers working on this code were able to drive an HDMI 2.1 panel via the RTD2173 chip with a Tigerlake laptop over DisplayPort.
From the driver side this DP-HDMI2.1 PCON support involves adding support for fixed rate link (FRL) training for use between the protocol converter chip and the HDMI 2.1 sink. For meeting HDMI 2.1 specifications, an extra lane is added by repurposing the TMDS clock channel. With fixed rate link training, it's possible to achieve 12 Gbps per lane.
More details via this patch series working on the DP-HDMI2.1 PCON support for the Intel i915 kernel driver. Unfortunately the VESA documentation on this feature is behind their membership wall and thus not generally available, but long story short this code is being worked on if you are looking to use a converter like the RTD2173 moving forward to achieve HDMI 2.1 over DisplayPort.