Most recent kernel where this bug did *NOT* occur: none
Distribution: Debian
Hardware Environment: IBM Thinkpad T20
Software Environment: Debian (mostly etch)
Problem Description:
This laptop contains two power resources:
 PSER and PSIO.
After boot, both are enabled, according to the boot messages. After S3,
/proc/acpi/power_resource/*/state indicates both resources as *OFF*. At least
for PSER, where the DSDT checks a register bit in an IBM-specific GPIO chip on
the mainboard, this is true. As this bit (called SSBY in IBM's DSDT) turns off
the power for the serial port driver, serial communication is not possible in
this state. The DSDT contains for the _SB_.PCI0.ISA_.UART._PR0 object a list
containing both PSER and PSIO. Setting this bit manually (on my thinkpad it is
outb -i 7 0x15EE 0x50, using XFree's outb, be carefull on other machines) does
enable serial communications again.

Steps to reproduce:
Boot a Thinkpad T20, suspend it to S3, resume it. Run
 cat /proc/acpi/power_resource/PSER/state
it reads "state: off" instead of "state: on"

Trackdown:
Not completely tracked. Somewhere in the pnp driver model, a suspend/resume
request should arrive, which should be passed to the acpi layer, finally ending
in acpi_power_transition.