Thanks Nico for your response.

> am expecting some register should set with eDP as interface and when
> display is connected
>
> any clue why the i915 OS driver was turning off DP display in case 2?
I assume the HPD signal doesn't get through to the software. 

[Rao]
You mean I need to check PORT_HOTPLUG_EN and PORT_HOTPLUG_STAT mmio offsets for this issue?
BIOS display is fine, Windows logo is also seen but there is no signal when "windows login" is reached 

It had similar behaviour w.r.t to ubuntu 18.04, I configured DDI1 to "DP with HDMI/DVI"

Can this issue be fixed with VBE data configured through BMP or it needs a fix from graphics MMIO?

Regards
Rao

On Fri, Jul 30, 2021 at 10:27 PM Nico Huber <nico.h@gmx.de> wrote:
On 30.07.21 18:59, Rao G wrote:
> Thanks Nico.
>
> HPD is active , measured the signal

Is your coreboot port public somewhere? If the hardware is fine, maybe
the firmware isn't?

>
> Configured Ports
> 1.DDI0- PortB - DP with HDMI/DVI is good in BIOS & OS
> 2.DDI1- PortC - DP with HDMI/DVI is good in BIOS, i915 was turning off the
> DP display (Never understood the reason)

It's very suspicious that these two behave differently. Does the HPD
signal (MMIO read) work for DDI0?

>
> So configured PortC with eDP
>
> If there is no way BIOS to detect the external display with MMIO registers
> when configured as eDP, Can i not turn off the DDI1/Port C at runtime in
> BIOS,

Maybe it's time to switch to an open-source solution? libgfxinit will
probably have the same issue, but it might be possible to get a rather
short delay.

> am expecting some register should set with eDP as interface and when
> display is connected
>
> any clue why the i915 OS driver was turning off DP display in case 2?

I assume the HPD signal doesn't get through to the software.

Nico