ThinkPad R40 hangs during ACPI power down

I've got an IBM ThinkPad R40 that hangs when I do a "shutdown -p".  It s
wedges after printing "Powering system off using ACPI".  The display
stays on, and judging by the heat, it seems that the CPU is on as well.
It doesn't respond to the keyboard, so I haven't been able to get into
DDB.  The only thing I can do at this point is to hold the power button
down to force it to power off.  The next boot is clean.

I've seen the same behaviour with September 8th and September 21st
versions of 5.1-CURRENT.

Attempting to use 'acpiconf -s" to suspend produces similar hangs.


I tried compiling a version of the kernel with the ACPI_DEBUG option
listed in NOTES, but buildkernel dies here:

cc -c -O -pipe -mcpu=pentiumpro -Wall -Wredundant-decls -Wnested-externs -Wstric
t-prototypes  -Wmissing-prototypes -Wpointer-arith -Winline -Wcast-qual  -fforma
t-extensions -std=c99 -g -nostdinc -I-  -I. -I/usr/src/sys -I/usr/src/sys/contri
b/dev/acpica -I/usr/src/sys/contrib/ipfilter -I/usr/src/sys/contrib/dev/ath -I/u
sr/src/sys/contrib/dev/ath/freebsd -D_KERNEL -include opt_global.h -fno-common -
finline-limit=15000 -fno-strict-aliasing  -mno-align-long-strings -mpreferred-st
ack-boundary=2 -ffreestanding -Werror  /usr/src/sys/dev/acpica/acpi_button.c
/usr/src/sys/dev/acpica/acpi_button.c: In function `acpi_button_fixed_handler':
/usr/src/sys/dev/acpica/acpi_button.c:246: error: `_Dbg' undeclared (first use i
n this function)
/usr/src/sys/dev/acpica/acpi_button.c:246: error: (Each undeclared identifier is
 reported only once
/usr/src/sys/dev/acpica/acpi_button.c:246: error: for each function it appears i
n.)
*** Error code 1

Stop in /usr/obj/usr/src/sys/ACPI_DEBUG.
*** Error code 1

Stop in /usr/src.

NOTES says that to use this option, the Intel code must have the
USE_DEBUGGER flag set.  I didn't see references to this in the code, but
there are a bunch of #ifdefs that refer to ACPI_DEBUGGER.  I tried
adding this to my kernel configuration, but config barfs on it.

The APCI asl file is at <http://people.freebsd.org/~truckman/r40.asl>
and the dmesg.boot is at
<http://people.freebsd.org/~truckman/r40.dmesg.boot>.  I downloaded the
ACPI spec and attempted to use it to decipher my asl file, but I decided
it was hopeless since I didn't even know far the ACPI code was getting.