[Intel-gfx] i915: LVDS display (or LVDS->DVI) via eDP as 2nd display

[Ville Syrjälä]

On Fri, Nov 11, 2016 at 02:19:36PM +0100, Stefan Roese wrote:
> Hi!
> 
> I'm currently trying to enable the 2nd display on our Bay Trail
> Atom E3845 SoC. This is on the Congatec SoM "conga-QA3":
> 
> http://www.congatec.com/en/products/qseven/conga-qa3.html
> 
> On this SoM, the eDP is converted to LVDS via an NXP PTN3460
> and available as LVDS on the baseboard. My current setup is that
> the 1st display is connected to HDMI1. This works just fine.
> In the production version I would like to use a LVDS display
> connected via eDP from the Bay Trail Atom. Since we don't have
> this LVDS display yet, I'm currently testing with this
> LVDS -> DVI adapter board:
> 
> http://www.congatec.com/de/produkte/zubehoer/conga-ldvi.html
> 
> So my current setup for this 2nd display is:
> 
> eDP -> LVDS -> DVI
> 
> which does not work.
> 
> Here my xrandr output:
> 
> Screen 0: minimum 8 x 8, current 1920 x 1200, maximum 32767 x 32767
> DP1 disconnected (normal left inverted right x axis y axis)
> DP2 disconnected (normal left inverted right x axis y axis)
> HDMI1 connected primary 1920x1200+0+0 (normal left inverted right x axis y axis) 597mm x 336mm
>    1920x1200     59.95* 
>    1920x1080     60.00  
>    1600x1200     60.00  
>    1680x1050     59.88  
>    1280x1024     75.02    60.02  
>    1280x800      59.91  
>    1152x864      75.00  
>    1024x768      75.03    60.00  
>    800x600       75.00    60.32  
>    640x480       75.00    59.94  
>    720x400       70.08  
> HDMI2 disconnected (normal left inverted right x axis y axis)
> VGA1 disconnected (normal left inverted right x axis y axis)
> VIRTUAL1 disconnected (normal left inverted right x axis y axis)
> 
> 
> When I now try to add and enable DP1 (this is the correct port for
> the eDP, right?), then I get these errors / warnings:

Not sure how the panel power for the LVDS output is hooked up, but if it
depends on the panel power pin from the soc, then you'll need to modify
the VBT to indicate that the port is really an eDP port as opposed to a
regular DP port (see intel_bios_is_port_edp()). Or you can of course just
hack up the driver to behave as if the VBT had indicated an eDP port
(good enough to confirm the theory at least).

-- 
Ville Syrjälä
Intel OTC