xf86-video-modesetting TearFree Gets Fixed Up For A/V De-Synchronization Issue

A few months back the generic xf86-video-modesetting X.Org driver added TearFree page-flipping support. The option eliminates screen tearing without the use of a compositor and was seen as a win by many for this generic DDX driver that works atop the modern DRM/KMS kernel drivers. But a rather annoying issue was discovered that could lead to audio/video synchronization problems was uncovered and is now fixed in the latest driver code.

When the TearFree mode for xf86-video-modesetting is enabled, it was discovered there could be inaccurate event timing and in turn causing audio/video de-synchronization with clients relying on the X.Org Server's Present extension.

These synchronization issues were traced back to some faulty assumptions in the Present code. The xf86-video-modesetting driver has fixed the "PresentCompleteNotify" timing for TearFree across the span of 11 driver patches.

This was worked on by Sultan Alsawaf who also took care of the TearFree implementation for the DDX driver. As of this morning that code has been merged to the X.Org Server.