[Bug 1815275] [NEW] logind fails to detect amdgpu external displays as external.

[Mercury]

Public bug reported:

So, with a Dell Precision 7530 outfitted with an AMD GPU, I can run into
issues relating to systemd not detecting that my laptop is docked.

This results in my booting the system, getting the login prompt on my
external displays, logging in, and having the system immediately
suspend.

This only happens when the BIOS has the displays being driven by the AMD
GPU instead of the integrated Intel GPU.

And the reason why this happens is that the amdgpu driver names the
outputs differently, specifically I end up with names like
DisplayPort-1-7.

The problem is that src/login/logind-core.c, in function
manager_count_external_displays, uses the following to detect external
displays (starting at line 561 at the moment):

                  FOREACH_STRING(i, "VGA-", "DVI-I-", "DVI-D-", "DVI-A-"
                                 "Composite-", "SVIDEO-", "Component-",
                                 "DIN-", "DP-", "HDMI-A-", "HDMI-B-", "TV-") {
  
                          if (startswith(dash, i)) {
                                  external = true;
                                  break;
                          }
                  }


As "DisplayPort-" is not on the list, logind decides that I must not be using an external display, so I'm probably not docked.

This is somewhat sub-optimal.

This is on Ubuntu 18.04, systemd package version 237-3ubuntu10.12.

** Affects: systemd (Ubuntu)
     Importance: Undecided
         Status: New

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https://bugs.launchpad.net/bugs/1815275

Title:
  logind fails to detect amdgpu external displays as external.

Status in systemd package in Ubuntu:
  New

Bug description:
  So, with a Dell Precision 7530 outfitted with an AMD GPU, I can run
  into issues relating to systemd not detecting that my laptop is
  docked.

  This results in my booting the system, getting the login prompt on my
  external displays, logging in, and having the system immediately
  suspend.

  This only happens when the BIOS has the displays being driven by the
  AMD GPU instead of the integrated Intel GPU.

  And the reason why this happens is that the amdgpu driver names the
  outputs differently, specifically I end up with names like
  DisplayPort-1-7.

  The problem is that src/login/logind-core.c, in function
  manager_count_external_displays, uses the following to detect external
  displays (starting at line 561 at the moment):

                    FOREACH_STRING(i, "VGA-", "DVI-I-", "DVI-D-", "DVI-A-"
                                   "Composite-", "SVIDEO-", "Component-",
                                   "DIN-", "DP-", "HDMI-A-", "HDMI-B-", "TV-") {
    
                            if (startswith(dash, i)) {
                                    external = true;
                                    break;
                            }
                    }

  
  As "DisplayPort-" is not on the list, logind decides that I must not be using an external display, so I'm probably not docked.

  This is somewhat sub-optimal.

  This is on Ubuntu 18.04, systemd package version 237-3ubuntu10.12.

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