Thinkpad T410 and display port

[fluca1978]

Hi all,
I'm running FreeBSD 13 on Lenovo Thinkpad T410. I've enabled 915kms module, so far so good.
However, when I plug an HDMI external display to the display port, the screen is not detected. Or better: it is detected at boot, but not after the system is already running. A trick I've found is to switch to a textual console (ALT-F1) and switch back to the video (ALT-F9), at that point the external output is activated.
Is there a way to push the video output to the video port by hitting Fn-F5, the Lenovo keys to do that?
Also, for some reason, if I mirror the external display, it is somehow trimmed on the low side, where I cannot see the bottom of the screen I see on the laptop monitor, even if I try to change the resolution.

Any help is appreciated.

 

[fluca1978]

This is the output of dmesg:

% dmesg | grep drm
drmn0: <drmn> on vgapci0
vgapci0: child drmn0 requested pci_enable_io
vgapci0: child drmn0 requested pci_enable_io
[drm] Unable to create a private tmpfs mount, hugepage support will be disabled(-19).
[drm] Got stolen memory base 0xbe000000, size 0x2000000
[drm] Supports vblank timestamp caching Rev 2 (21.10.2013).
[drm] Driver supports precise vblank timestamp query.
[drm] Connector LVDS-1: get mode from tunables:
[drm]   - kern.vt.fb.modes.LVDS-1
[drm]   - kern.vt.fb.default_mode
[drm] Connector VGA-1: get mode from tunables:
[drm]   - kern.vt.fb.modes.VGA-1
[drm]   - kern.vt.fb.default_mode
[drm] Connector HDMI-A-1: get mode from tunables:
[drm]   - kern.vt.fb.modes.HDMI-A-1
[drm]   - kern.vt.fb.default_mode
[drm] Connector DP-1: get mode from tunables:
[drm]   - kern.vt.fb.modes.DP-1
[drm]   - kern.vt.fb.default_mode
[drm] Connector HDMI-A-2: get mode from tunables:
[drm]   - kern.vt.fb.modes.HDMI-A-2
[drm]   - kern.vt.fb.default_mode
[drm] Connector HDMI-A-3: get mode from tunables:
[drm]   - kern.vt.fb.modes.HDMI-A-3
[drm]   - kern.vt.fb.default_mode
[drm] Connector DP-2: get mode from tunables:
[drm]   - kern.vt.fb.modes.DP-2
[drm]   - kern.vt.fb.default_mode
[drm] Connector DP-3: get mode from tunables:
[drm]   - kern.vt.fb.modes.DP-3
[drm]   - kern.vt.fb.default_mode
[drm] RC6 disabled, disabling runtime PM support
[drm] Initialized i915 1.6.0 20190822 for drmn0 on minor 0
name=drmn0 flags=0x0 stride=5760 bpp=32

and what is puzzling me is that, as far as I understand, the display port is disconnected even when it is working:

% sysctl -a | grep  DP
sys.class.drm.card0-DP-3.modes:  
sys.class.drm.card0-DP-3.dpms: Off
sys.class.drm.card0-DP-3.enabled: disabled
sys.class.drm.card0-DP-3.status: disconnected
sys.class.drm.card0-DP-2.modes:  
sys.class.drm.card0-DP-2.dpms: Off
sys.class.drm.card0-DP-2.enabled: disabled
sys.class.drm.card0-DP-2.status: disconnected
sys.class.drm.card0-DP-1.modes:  
sys.class.drm.card0-DP-1.dpms: Off
sys.class.drm.card0-DP-1.enabled: disabled
sys.class.drm.card0-DP-1.status: disconnected
dev.pcm.3.%desc: Intel Ibex Peak (HDMI/DP 8ch)
dev.pcm.2.%desc: Intel Ibex Peak (HDMI/DP 8ch)
        Pin cap: 0x09000094 PDC OUT HDMI DP HBR
        Pin cap: 0x09000094 PDC OUT HDMI DP HBR
        Pin cap: 0x09000094 PDC OUT HDMI DP HBR

I confirm that switching from a X display to a virtual terminal activates the display port.