[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 08:56:35 PDT 2011


--- Comment #6 from Alex Deucher <agd5f at yahoo.com> 2011-08-09 08:56:34 PDT ---
(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.

> 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

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