[PATCH] ugly patch for DRM based XSync VBLANK support
jbarnes at virtuousgeek.org
Mon Mar 13 13:28:26 PST 2006
On Monday, March 13, 2006 3:41 am, Michel Dänzer wrote:
> > I hadn't even considered that... yeah it seems like a problem. We
> > could just disable it in a MergedFB environment and hope people use
> > something else (maybe that will become possible with a proper memory
> > manager?), or somehow provide per-head stuff anyway?
> Or maybe we could just make this Xinerama aware somehow. No idea if
> that's even possible with the driver-specific Xinerama implementations
I'll have to look around to see if that's doable. I don't know much
about Xinerama or its implementation.
> Anyway, thanks for finally attempting to put the DRM vblank signal
> interface to good use! I wonder if there wouldn't be a better way than
> the BlockHandler to 'get the word out' that the counter has increased,
> but maybe there is none without a poll/select interface from the DRM.
Well, right now it's in the Wakeup handler, but I agree that it's not
ideal. The Wakeup handler could be called a long time after the actual
signal was received, making it vulnerable to scheduling.
> You may want to determine the current vblank count by calling
> drmWaitVBlank() with vbl.request.type=DRM_VBLANK_RELATIVE and
> vbl.request.sequence=0 instead of just increasing it monotonically on
> each signal to avoid missing vblanks, e.g. due to scheduling latency.
Good point, I'll fix that. Scheduling latency is definitely a problem.
> Also, you don't seem to initialize the requested signal number. I
> wonder if that could be why you get EPERM instead of EINVAL.
Oops! That's definitely a bug, I'll fix it and see if anything changes
(though I won't be able to get to it until this weekend at the
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