Distribution:  Fedora-Core-2
Hardware Environment: Gateway Laptop Solo 9550
Software Environment: official 2.6.7 kernel + swsusp2 + acpi-20040326
Problem Description: On my laptop, changes in the ac status is not reported. No
event is produced. The ac status is read properly, and when read produces the
proper change (lcd light intensity changed according to ac status).

I tracked down and fixed the problem:
My dsdt uses Notify (\_SB.ACAD, 0x00) to notify the os of AC power status changes. 
The current notify handler (acpi_ev_queue_notify_request in events/evmisc.c) use
the notify value to decide upon an device or system event handler (.

Now the AC handler is a device but because of the notify value of 0 (bus check)
it will not be called. Even if it was called it only handles notify values of
0x80.

A fix for this would be to chnage my dsdt to use Notify (\_SB.ACAD, 0x80)
instead. But I found another way by modifying the ac.c module. I register the
handler for system and device and habdle the bus_check value. This might be
usefull to others in case other peoples dsdt have a similar problem. 

I don't know if this is a problem seen in many dsdt, but this should fix this
type of problems and I don't think it will have any side effect.

Here is the patch:
--- ac.c.orig   2004-08-15 14:34:03.000000000 -0400
+++ ac.c        2004-08-15 14:37:43.000000000 -0400
@@ -219,6 +219,7 @@
  
        switch (event) {
        case ACPI_AC_NOTIFY_STATUS:
+       case ACPI_NOTIFY_BUS_CHECK:
                acpi_ac_get_state(ac);
                acpi_bus_generate_event(device, event, (u32) ac->state);
                break;
@@ -272,6 +273,15 @@
                goto end;
        }
  
+       status = acpi_install_notify_handler(ac->handle,
+               ACPI_SYSTEM_NOTIFY, acpi_ac_notify, ac);
+       if (ACPI_FAILURE(status)) {
+               ACPI_DEBUG_PRINT((ACPI_DB_ERROR,
+                       "Error installing system notify handler\n"));
+               result = -ENODEV;
+               goto end;
+       }
+
        printk(KERN_INFO PREFIX "%s [%s] (%s)\n",
                acpi_device_name(device), acpi_device_bid(device),
                ac->state?"on-line":"off-line");
@@ -307,6 +317,12 @@
                ACPI_DEBUG_PRINT((ACPI_DB_ERROR,
                        "Error removing notify handler\n"));
  
+       status = acpi_remove_notify_handler(ac->handle,
+               ACPI_SYSTEM_NOTIFY, acpi_ac_notify);
+       if (ACPI_FAILURE(status))
+               ACPI_DEBUG_PRINT((ACPI_DB_ERROR,
+                       "Error removing system notify handler\n"));
+
        acpi_ac_remove_fs(device);
  
        kfree(ac);