[Bug 1716857] Re: nvidia-drm.modeset=1, gdm3 and optimus laptop results in no external monitors detected by Xorg

[Kai-Chuan Hsieh]

Test on Intel Tiger Lake platform with nvidia dGPU (N17S-G5
PCI\VEN_10DE&DEV_1C94).

Distribution: Ubuntu
Codename: focal
kernel: 5.6.0-1018-oem
NV driver: 440.100
nvidia_drm modeset=1
gdm3: 3.34.1-1ubuntu1
xserver-xorg-core: 2:1.20.8-2ubuntu2.1

The device can detect external 4K/UHD monitor sucessfully by HDMI or DP.
It seems the original issue is not able to reproduce on this machine.
However, the modeset has to be enabled for https://bugs.launchpad.net/ubuntu/+source/nvidia-graphics-drivers-390/+bug/1769857/comments/5, but it is disabled by default currently.

** Attachment added: "Attach my external monitors edid for reference"
   https://bugs.launchpad.net/ubuntu/+source/gdm3/+bug/1716857/+attachment/5392513/+files/philips-edid

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https://bugs.launchpad.net/bugs/1716857

Title:
  nvidia-drm.modeset=1, gdm3 and optimus laptop results in no external
  monitors detected by Xorg

Status in gdm3 package in Ubuntu:
  Opinion
Status in nvidia-graphics-drivers-375 package in Ubuntu:
  Confirmed
Status in nvidia-graphics-drivers-418 package in Ubuntu:
  Confirmed
Status in nvidia-graphics-drivers-430 package in Ubuntu:
  Confirmed
Status in nvidia-graphics-drivers-435 package in Ubuntu:
  Confirmed
Status in systemd package in Ubuntu:
  Confirmed

Bug description:
  Context:
  17.10 development packages, nvidia binary driver 375, modeset=1 for the nvidia driver.
  ubuntu desktop (gnome shell), fresh install
  ThinkPad W520 in Nvidia Optimus bios mode.
  Nvidia profile.

  Result:
  no external monitors are detected.
  xrandr does not even list them as disconnected (normally it would list five external disconnected monitors)

  
  lsmod 
  shows that nvidia driver is loaded
  and the modesetting is working at some level because there is no tearing on the laptop panel

  
  Note: modeset=1 is the only way to get flicker-free graphics on the laptop panel. modeset=1 is not the default setting but it is highly desirable. 

  It works if lightdm is used which is why I have reported this against gdm3
  My sessions in this configuration have mostly crashed after a few minutes with a gdm3 fail whale message in syslog but nothing else looks interesting.

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