[Bug 39696] dual head: different vert refresh freq, applications sync to the wrong one

bugzilla-daemon at freedesktop.org bugzilla-daemon at freedesktop.org
Tue Aug 9 07:28:25 PDT 2011


--- Comment #5 from Klaus Kusche <klaus.kusche at computerix.info> 2011-08-09 07:28:24 PDT ---
(In reply to comment #4)
> (In reply to comment #3)
> > > > and with synchronized vertical retrace?
> > > 
> > > There's no mechanism for that yet in general. However, if you manage to use the
> > > same mode for both displays, you might be able to source both of them off the
> > > same CRTC, in which case they should be perfectly synchronized.
> > 
> > Can this be set using xrandr or something else?
> Yeah, using the --crtc option. With xrandr --verbose you can see which CRTCs an
> output can use.

Doesn't work the way we would like it:
* All outputs can be connected to all CRTC's.
* Default is LVDS:0, DP: 1
* Even if the mode is exactly the same: As soon as I connect the DP to CRTC 0
using xrandr, xrandr automatically reconnects LVDS to CRTC 1 (and if I
reconnect the LVDS, DP is also switched). Hence, they can exchange CRTC's, but
running both from the same CRTC seems to be impossible.

However, according to xrandr -- verbose they are not clones. 
How do I set them to clone mode?

> > > > 2.) Is there a way to switch 3D and video application sync
> > > > from the internal to the external vsync rate?
> > > 
> > > There's no such mechanism for 3D yet.
> > 
> > From the user's point of view, xvattr would be expected to set both?
> Not sure how xvattr could be expected to affect anything but XVideo.

I didn't mean that I expect xvattr to do that,
I just wanted to say that the average user would expect that a single setting
controls both.

> Some random ideas: All other things being equal, the driver could synchronize
> to the CRTC of the primary output, which can be changed using xrandr --primary.
> Or if that's not good enough, we could add special RandR properties for this.

Currently both Xv and GL sync to LVDS by default,
no matter which output is primary,
and no matter which CRTC they use: 
Even if DP is primary and CRTC 0, sync is on LVDS.

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