[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 09:07:03 PDT 2011


--- Comment #7 from Klaus Kusche <klaus.kusche at computerix.info> 2011-08-09 09:07:03 PDT ---
(In reply to comment #6)
> (In reply to comment #5)
> > 
> > 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?
> We disable cloning of certain encoders in the driver.  At the hardware level,
> you can source multiple encoders to the same crtc, but there are too many
> encoder specific limitations in most cases that make it hard to support cloning
> from the same crtc.  DP and LVDS are not possible for example as they use
> different clocking for the encoders.  LVDS is direct clocked from the PPLL
> while DP uses fixed clock derived from the DCPLL, so you can't drive both off
> the same crtc easily, at least not the way the driver is currently structured.

That would also explain why I still have a moving tear line even when using
exactly the same modeline on both - their base clock seems to differ slightly.

> > 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.
> You might try assigning primary flag to the DP output.
> xrandr --output DisplayPort-0 --primary

That's what I tried, but both GL and Xv still sync to LVDS?

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