My Mac Mini has two monitors attached to it: a Mac Display one, on its thunderbolt port, and a small generic monitor attached to its HDMI port (using a HDMI-to-VGA adapter). This is how xrandr sees them:
user@mini:~$ xrandr
Screen 0: minimum 320 x 200, current 3584 x 1440, maximum 16384 x 16384
VGA-1 disconnected (normal left inverted right x axis y axis)
HDMI-1 disconnected (normal left inverted right x axis y axis)
DP-1 connected primary 2560x1440+1024+0 (normal left inverted right x axis y axis) 597mm x 336mm
2560x1440 59.95*+
1280x720 59.86
HDMI-2 disconnected (normal left inverted right x axis y axis)
HDMI-3 connected 1024x768+0+0 (normal left inverted right x axis y axis) 304mm x 228mm
1024x768 60.00*+ 75.03 70.07
1920x1080 60.00 59.94
1280x720 60.00 59.94
832x624 74.55
800x600 72.19 75.00 60.32
720x480 60.00 59.94
640x480 75.00 72.81 60.00 59.94
720x400 70.08
DP-2 disconnected (normal left inverted right x axis y axis)
DP-3 disconnected (normal left inverted right x axis y axis)
user@mini:~$
user@mini:~# uname -a
Linux mini 6.1.0-18-amd64 #1 SMP PREEMPT_DYNAMIC Debian 6.1.76-1 (2024-02-01) x86_64 GNU/Linux
user@mini:~#
The computer is configured (in xfce's power manager) to go into "suspend mode" after an hour. When that happens, dmesg tells me it cuts power to the thunderbolt controller:
[Tue Mar 12 20:40:56 2024] ata1.00: Entering standby power mode
[Tue Mar 12 20:40:56 2024] ACPI: EC: interrupt blocked
[Tue Mar 12 20:40:56 2024] pcieport 0000:04:00.0: quirk: cutting power to Thunderbolt controller...
[Tue Mar 12 20:40:56 2024] pcieport 0000:04:00.0: quirk_apple_poweroff_thunderbolt+0x0/0xf0 took 313017 usecs
[Tue Mar 12 20:40:56 2024] ACPI: PM: Preparing to enter system sleep state S3
[Tue Mar 12 20:40:56 2024] ACPI: EC: event blocked
[Tue Mar 12 20:40:56 2024] ACPI: EC: EC stopped
[Tue Mar 12 20:40:56 2024] ACPI: PM: Saving platform NVS memory
[Tue Mar 12 20:40:56 2024] Disabling non-boot CPUs ...
[Tue Mar 12 20:40:56 2024] smpboot: CPU 1 is now offline
[Tue Mar 12 20:40:56 2024] smpboot: CPU 2 is now offline
[Tue Mar 12 20:40:56 2024] smpboot: CPU 3 is now offline
[Tue Mar 12 20:40:56 2024] smpboot: CPU 4 is now offline
[Tue Mar 12 20:40:56 2024] smpboot: CPU 5 is now offline
[Tue Mar 12 20:40:56 2024] smpboot: CPU 6 is now offline
[Tue Mar 12 20:40:56 2024] smpboot: CPU 7 is now offline
[Tue Mar 12 20:40:56 2024] ACPI: PM: Low-level resume complete
[Tue Mar 12 20:40:56 2024] ACPI: EC: EC started
which in turn causes the Apple Display monitor connected to its mini-displayport to be listed as disconnected. Note my generic monitor is still being shown as connected. I do not know which monitor is in the DP-3 port. All I can say is the resolution (2560x1440) matches that of the Apple monitor.
user@mini:~$ xrandr
Screen 0: minimum 320 x 200, current 3584 x 1440, maximum 16384 x 16384
VGA-1 disconnected (normal left inverted right x axis y axis)
HDMI-1 disconnected (normal left inverted right x axis y axis)
DP-1 disconnected primary 2560x1440+1024+0 (normal left inverted right x axis y axis) 0mm x 0mm
HDMI-2 disconnected (normal left inverted right x axis y axis)
HDMI-3 connected 1024x768+0+0 (normal left inverted right x axis y axis) 304mm x 228mm
1024x768 60.00*+ 75.03 70.07
1920x1080 60.00 59.94
1280x720 60.00 59.94
832x624 74.55
800x600 72.19 75.00 60.32
720x480 60.00 59.94
640x480 75.00 72.81 60.00 59.94
720x400 70.08
DP-2 disconnected (normal left inverted right x axis y axis)
DP-3 disconnected (normal left inverted right x axis y axis)
2560x1440 (0x497) 241.500MHz +HSync -VSync
h: width 2560 start 2608 end 2640 total 2720 skew 0 clock 88.79KHz
v: height 1440 start 1443 end 1448 total 1481 clock 59.95Hz
user@mini:~$
When I log back into the mini, the host seems to wake up, and so does the monitor in the HDMI port, but the Apple Monitor is still being reported as disconnected. If I briefly unplug the Apple monitor's thunderbolt cable, this monitor will wake up.
Now, before I blame the thunderbolt port, I have placed the 1024x768 monitor, using a mini-displayport to VGA adapter, in the mini's thunderbolt port: that monitor will come out of its powersave mode just fine. The same goes for another monitor I have, which was connected using a mini-displayport to HDMI adapter.
Looking at some threads here, I found some old ones discussing this is a hotplugging issue. Given that unplugging and hotplugging the monitor turns it on I would say part of that must have been solved. I would like not to have to disconnect the monitor every time I come back after it was turned off for the same reasons I would rather avoid hotplugging a PCIe card. So, what can I do to emulate a hotplugging event while leaving the thunderbolt cable alone?
