[Bug 73850] [gm45] allow cloning one display together with an extended desktop across two displays

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=73850

--- Comment #9 from Ville Syrjala <ville.syrjala at linux.intel.com> ---
(In reply to comment #8)
> I enabled cloning for my LVDS1 output as well (in the source) and this works
> correctly in combination with VGA.
> 
> When I try to clone LVDS1 with HDMI1, it appears that the HDMI1 output loses
> signal as soon as I switch on LVDS1. When I turn LVDS1 off, the signal to
> HDMI1 returns again.
> 
> Could there be a reason which would make cloning between HDMI1 and LVDS1
> impossible or could this work with another trick? The resolutions which my
> LVDS1 screen and HDMI1 output support are much closer to each other than the
> screen I have on VGA1, so if it would be possible to clone HDMI1 and LVDS1
> it would be the most useful to me.

The spec for gen4 hardware is a bit confused whether LVDS+HDMI should work. It
says that the following note applies to the LVDS+HDMI combination:
"No internal LVDS and sDVO or DP on same pipe"
So the note that's supposed to apply to HDMI doesn't mentiond HDMI :)
I think this was just an oversight and the LVDS+HDMI combination is in fact not
supported. The fact that it is listed as unsupported in the spec for more
recent hardware supports this conclusion as well.

So I think what we can do is enable cloning for LVDS+VGA and HDMI+VGA.

The HDMI+HDMI case is a bit more complicated since we run into problems with
the infoframes. But on g4x hardware we anyway have that problem already even if
we don't clone between the HDMI outputs. So I think we won't lose anything by
allowing that too on g4x. Whether we should allow it for more recent hardware
is an open question.

I'll try to come up with a sane patch for this soon.

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