Implementation of https://lkml.org/lkml/2021/5/12/764 now feature complete albeit not fully tested.
I have not yet corrected the DSC behavior and double checked the dithering behavior. I release the feature complete patch series now anyways so that work on the userspace implementation can start.
I have no DP MST splitter at hand. I tried my best to not break anything, but if one who has one could test it would be very helpful.
amdgpu in the former implementation was full color range only, albeit there was a path prepared for limited color range on both rgb and ycbcr encoding, which was never selected however. With the Broadcast RGB property, a user can now select this program path.
On i915 Broadcast RGB still only affects rgb as ycbcr was and is always limited with this driver, which I didn't change.
gma500 driver still uses it's own implementation of the "Broadcast RGB" property, which doesn't have an "Automatic" setting. I too didn't touch this as I can't test a corresponding card.