The HDMI Forum, the body which creates, regulates and licenses that well established port, told AMD that they are not allowed to make an open source driver using version 2.1 of that standard.
As consequence this means that people using open source drivers for GPUs of any kind with HDMI will not have the same set of resolutions and frame rate available as Windows, instead they will have to use the proprietary ones under Linux/FreeBSD if available. Open source drivers therefore will only offer an inferior subset of what Windows can do.
Displayport on the other hand is not limiting access to similar resolutions/frame rates that for open source drivers of any kind.
arstechnica.com
As consequence this means that people using open source drivers for GPUs of any kind with HDMI will not have the same set of resolutions and frame rate available as Windows, instead they will have to use the proprietary ones under Linux/FreeBSD if available. Open source drivers therefore will only offer an inferior subset of what Windows can do.
Displayport on the other hand is not limiting access to similar resolutions/frame rates that for open source drivers of any kind.
HDMI Forum to AMD: No, you can’t make an open source HDMI 2.1 driver
Linux users can't hit the same resolutions and speeds as Windows—or DisplayPort.
arstechnica.com