Xdamage isn’t a thing if you’re using a compositor for what it’s worth. It’s more expensive to try to incrementally render than to just render the entire scene (for a GPU anyway).

And regardless, the HW path still involves copying the entire frame buffer - it’s literally in the name.

At the software level yes, but it seems nobody has taken the time to do this at the hardware level as well. This is LG's stab at it.

What’s your metal model of what happens when a dirty region is updated and now we need to get that buffer on the display?

You forget that all modern UI toolkits brag about who has the highest frame rate, instead of updating only what's changed and only when it changes.