Waiting for vertical refresh on Intel 965 and 945 chips in recent git
xavier.bestel at free.fr
Fri Jun 8 08:44:04 PDT 2007
On Fri, 2007-06-08 at 08:27 -0700, Jesse Barnes wrote:
> > Why can't vblank be enabled only when the DRM_IOCTL_WAIT_VBLANK ioctl is
> > called ? Is that because OpenGL hangs on to it ?
> The problem is that GL exposes an absolute vblank event count to clients. So
> we have to keep an accurate count or applications could hang or refresh on
> the wrong event. Fortunately, some devices have internal vblank counters, so
> we can disable the interrupt and only enable it when some client is actively
> waiting, and use the register to keep track of the absolute number of events
> when interrupts were disabled.
Perfectly clear. I understand now the discussions about using some time-
based counters for some hardware (obviously the other kind of hw).
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