Hard drive power saving

[Matthew Garrett]

Having thought about this for a bit, and having come up with a (just 
about) plausible explanation for the problem, I've reenabled hard drive 
power management in the AC mode change script.

The problem was hangs associated with switching from AC to battery, or 
vice-versa. I /think/ the cause for this may have been down to the 
laptop hardware sending IDE commands on power change (such as to slow 
down CD drive speed), and sending the APM command at the same time may 
have then hung the IDE bus. To get around this, I've delayed the sending 
of commands until a while after the state change.

It's possible that this isn't the problem, and if so it's likely that 
it'll suddenly reappear and start biting people. So, it would be helpful 
if you could let me know if changing your power source suddenly results 
in the machine hanging (either at the time of the event, or the next 
time it tries any disk access).

Thanks,
-- 
Matthew Garrett | mjg59 at srcf.ucam.org