[FlareCoding]

Summary

An output relit on a DisplayPort short pulse, the brief hotplug pulse by which a monitor asks for its DisplayPort registers to be read, named no monitor in gfxfb's GET_OUTPUT, as the relight left out the monitor's identity, the maker, name, product code and serial number its EDID gives.

Changes

• A relit output names its monitor again: relight_at_lit_timing copies the head's lit_monitor into the one-timing output_modes it builds from what the head kept, as every other light takes the identity from its EDID read. GET_OUTPUT then names the same monitor before and after the relight, so stlxdm, which finds its stored layouts by these identities, sees no new monitor.
• The new read is documented: lit_monitor's comment names set_up and the driver task as its only writers, so the driver task, on which the relight runs, may read it without the output lock.
• Checked by a mutation: with the copy dropped, the x86_64 suite fails only the extended test, whose two new checks find the relit output's maker and name empty.
• Tests: a_short_pulse_relights_an_output_whose_link_is_lost_at_the_timing_it_had also checks that the relit output is reported lit with its EDID's maker and name, AOC and AG241QG4.