Comment 13 for bug 1998716

FYI, in case anyone wants to add their monitor (and whether it succeeds or fails at suspending with the Ubuntu raspi kernel) to this ticket:

$ cp /sys/devices/platform/gpu/drm/card1/card1-HDMI-A-1/edid hdmi0-monitor.edid
$ cp /sys/devices/platform/gpu/drm/card1/card1-HDMI-A-2/edid hdmi1-monitor.edid

As you may guess, hdmi0-monitor.edid is the EDID for the monitor plugged into HDMI0 (the socket closest to the USB-C power port on the Pi4, and the socket closest to the uSD slot on the Pi400), whilst hdmi1-monitor.edid is the EDID for the monitor plugged into HDMI1. If you have no monitor connected to a socket, you'll still get an EDID file but it'll be 0 bytes. A valid EDID file should be 256 bytes (or more? I forget the details of EDID, but there's some extended blocks I vaguely recall).

Upload valid EDID files to https://www.edid.tv/edid/upload/binary/ if you wish (bear in mind this will share the serial # of your monitor but I don't think there's any particular security risk in that), and add the link here along with whether or not this particular monitor suspends successfully or not.