Oh, and this was with acpi_idle. This machine already failed to resume from S3 with intel_idle since forever, as detailed in https://bugzilla.kernel.org/show_bug.cgi?id=107151 but acpi_idle worked fine until now.
can you disable (in sysfs) all C states other than C0/C1 and see if that makes it go away? that would point at the problem pretty clearly...
