..
When I rebuilt with all debug stuff on, the kernel was worse than
before, and just gave the "black screen of nothing" on resume,
with a hung system.
At least before the system didn't hang.
Now I've just booted with a differently configured kernel,
with only about half of the debug flags turned on.
This one resumes from suspend, and *with* working USB too.
Ugh. Gotta love it when the bug is so subtle that turning on
the debug flags makes it (1) get worse, and/or (2) get cured.
Here's the abbreviated diff between broken (no USB on resume, no hang),
and working (good USB, no hang) .config files.
-CONFIG_RTC_CLASS=y
+# CONFIG_RTC_CLASS is not set