Xserver driver merging pros & cons

[Dave Airlie]

> If you're talking enterprise distros though, that means committing to at
> least one long-term support stable branch, that you backport new driver
> support to
> for years, not just the 6 months until the next one.

Just a note from an enterprise distro maintainer, we are currently
rebasing the X server/Mesa stacks as much as we can.

The problem with doing backports is you end up running combinations of
totally untested variants from upstream. Like does anyone upstream run
Xorg ATI 6.14.2 against Xserver 1.1? of course not. The thing is that
although <x= random percentage> of the driver code that is compatible
with older servers, there is <100-x> of the code that has subtle bugs
that aren't obvious ABI breaks. Inherent reliance on fixes in the fb
layer, EXA layer, damage, randr layers etc is nearly impossible to
find in advance. Like if Intel made SNA the default, the number of
server fixes it requires to operate correctly is major, whereas it'll
build against any of those servers at an ABI level.

Dave.