Hard drive power saving

[Matt Zimmerman]

On Thu, Feb 16, 2006 at 12:39:46AM +0000, Matthew Garrett wrote:
> 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.

[for those playing along at home, this is
https://launchpad.net/distros/ubuntu/+source/linux-source-2.6.15/+bug/12483]

> 
> 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.

At least for me, there was no temporal correlation between a change of power
source and the hang; I was able to reproduce it after a clean boot of the
system on battery power even.

> 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).

It's possible that some deep, mysterious bug has been fixed elsewhere as
well...

-- 
 - mdz