[Bug 104072] [GFX][SNB] Connecting three monitors one of them lost video signal

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=104072

Ville Syrjala <ville.syrjala at linux.intel.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEEDINFO                    |RESOLVED
         Resolution|---                         |NOTABUG

--- Comment #6 from Ville Syrjala <ville.syrjala at linux.intel.com> ---
(In reply to Elizabeth from comment #4)
> This is still easily reproduce with 4.16.0-rc7-commit617cddf0. Whenever SNB
> laptop has DP and VGA connected the video signal will be lost in both
> monitors.
> If i use 
>    
>      $ xrandr --output VGA-1 --auto 
> 
> I'll get video in the VGA monitor, but if I do 
> 
>      $ xrandr --output DP-1 --auto
> 
> It will return:
> 
>       xrandr: cannot find crtc for output DP-1
> 
> If only is used one output at the time, besides the laptop's display
> (LVDS-1), it works properly.

SNB only has two pipes so you can only drive two independent displays. To get
three outputs at the same time you need to make sure two of the outputs are VGA
and HDMI, and that they are using the exact same mode.

Ie. you can simply never enable DP+VGA+LVDS simultaneously on SNB.

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