libddcutil behaves differently/fails after a hotplug compared to ddcutil

[digitaltrails]

I did a hotplug of the Beng BegQ T2200HD, after which libddcutil correctly detected the new monitor, but an attempt to use libddcutil getvcp failed returning DDCRC_INTERNAL_ERROR. The command-line ddcutil worked fine, both with detect and setvcp.

I traced this back to src/ddc/ddc_displays.c inside

ddc_validate_display_ref(Display_Ref * dref, bool basic_only, bool 
require_not_asleep)

Where it appear that the drm_connector was NULL:

else if (drm_enabled && !basic_only) {
              if (!dref->drm_connector)    <----------------------- NULL
                  ddcrc = DDCRC_INTERNAL_ERROR;

Suspecting the driver had not initialised some aspect of drm, I then hacked the call to ddc_validate_display_ref to force basic_only, and then the setvcp worked.

I then rebooted figuring drm would then be correctly initialised. Sure enough the basic_only hack was no longer required, a getvcp via libddcutil worked just fine.

I don't think you can trust the drm structures if the Nvidia driver is in play. I suppose this could be covered off with documentation. Or maybe an option to completely switch off drm.