Mythtv playing way to fast using DRM VBlank ioctl

Michel Dänzer michel at
Fri Mar 31 07:30:48 PST 2006

On Thu, 2006-03-30 at 13:57 -0500, Greg Stark wrote:
> "Alex Deucher" <alexdeucher at> writes:
> > On 30 Mar 2006 11:58:59 -0500, Greg Stark <gsstark at> wrote:
> > >
> > > I'm still having trouble getting mythtv running displaying on my R350 Radeon.
> > > I've defeated the bogus mergedfb dot clocks with an LD_PRELOAD hack but now I
> > > have a new problem.
> > 
> > Once again if you are using mergedfb the drm vblank won't work for you
> > on crtc2 since it only applies to the first crtc.  AFAIK, there's no
> > drm support for vblank on crtc2.

Indeed, but it shouldn't be hard to add it. Of course, apps would then
still have to know which CRTC they need to sync to.

> It seems like it would be better to fail in some way, perhaps printk'ing a
> message, than to silently return immediately if that's what it's doing.

MythTV does check for it not returning -EINVAL (which means waiting for
vblank is not supported, at least not with the arguments supplied to the
ioctl), doesn't it?

Earthling Michel Dänzer      |     Debian (powerpc), X and DRI developer
Libre software enthusiast    |

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