linux-kernel - Re: [linux-pm] Power management for SCSI

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Date:	Fri, 22 Aug 2008 18:14:51 -0400 (EDT)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Pavel Machek <pavel@...e.cz>
cc:	Oliver Neukum <oneukum@...e.de>,
	<linux-pm@...ts.linux-foundation.org>,
	<James.Bottomley@...senpartnership.com>,
	Linux-pm mailing list <linux-pm@...ts.osdl.org>,
	kernel list <linux-kernel@...r.kernel.org>, <teheo@...ell.com>
Subject: Re: [linux-pm] Power management for SCSI

On Fri, 22 Aug 2008, Pavel Machek wrote:

> Hi!
> 
> > > - suspending has side effects
> > 
> > I'm not sure what you mean by that.  Suspension always has side effects 
> > of one kind or another.
> > 
> > > Suspension in USB has always side effects. That's not true for other
> > > subsystems.
> > 
> > Name one.  At the very least, suspending a device means you can't use
> > it again without first calling the driver's resume method.  That's a 
> > side effect.
> 
> IDE, actually. I don't think it is relevant, but you can do hdparm -y,
> and it will automatically spin up when you try to talk to it next
> time.

It's a matter of definitions...  "hdparm -y" doesn't call the driver's 
suspend method, so in some sense it isn't truly a suspend.

But it's true that some systems can power down more or less
transparently (with restart latency as the only visible side effect).

Alan Stern

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