Most likely the hotplug detect line from your display.
The firmware would try reading the display EDID even if HPD wasn't asserted, and would accept an answer if it was forthcoming.
The vc4 DRM driver follows the HDMI spec more closely and will only try reading the EDID if HPD is asserted.
It's slightly odd that /dev/fb0 disappears - DRM will create the framebuffer when the first output of the DRM card provides a resolution, but doesn't delete it again if the output becomes disabled.
The firmware would try reading the display EDID even if HPD wasn't asserted, and would accept an answer if it was forthcoming.
The vc4 DRM driver follows the HDMI spec more closely and will only try reading the EDID if HPD is asserted.
It's slightly odd that /dev/fb0 disappears - DRM will create the framebuffer when the first output of the DRM card provides a resolution, but doesn't delete it again if the output becomes disabled.
Statistics: Posted by 6by9 — Tue Mar 18, 2025 1:52 pm