[Nouveau] nouveau-ddx: Improvements to DRI2 kms pageflip and swapbuffers support.

[Mario Kleiner]

Hi. The following series of three patches provides some
improvements and bug fixes to DRI2 swap scheduling, kms pageflipping and
pageflip completion timestamping. And a fix for desktop corruption
when switching between redirected and unredirected fullscreen windows.

These are mostly direct translations of similar functionality and bug-fixes
from the intel ddx and ati ddx. All successfully tested on a GeForce-7800
GTX and QuadroFX-570 in single display mode and dual-display modes (xinerama
desktop spanning and clone mode).

I'll send another separate patch for the Linux nouveau-kms driver's pageflip
completion routine, so it reports back proper pageflip completion events
with correct timestamp and vblank count (according to OML_sync_control spec).

Lucas Stach has an almost finished patch for the nouveau-kms driver to implement
the drm high-precision vblank timestamping hook. All patches taken together
were tested on NV-47 with high precision measurement equipment. Results show
that the pageflip completion timestamps reported with these patches are accurate
with respect to reality, with a residual error of less than 40 microseconds.

Please review and apply as you see fit.

thanks,
-mario