linux-kernel - Re: Power management for SCSI

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Date:	Wed, 13 Aug 2008 16:47:42 +0200
From:	Oliver Neukum <oneukum@...e.de>
To:	Alan Stern <stern@...land.harvard.edu>
Cc:	Pavel Machek <pavel@...e.cz>,
	kernel list <linux-kernel@...r.kernel.org>,
	"Linux-pm mailing list" <linux-pm@...ts.osdl.org>,
	James.Bottomley@...senpartnership.com, teheo@...ell.com
Subject: Re: Power management for SCSI

Am Mittwoch 13 August 2008 16:31:03 schrieb Alan Stern:
> On Wed, 13 Aug 2008, Pavel Machek wrote:
> 
> > From: Alan Stern <stern@...land.harvard.edu>
> > 
> > Add support for autosuspend/autoresume. Lowlevel driver can use it to
> > spin the disk down and power down its SATA link, to turn off the USB
> > interface, etc.
> > 
> > Spinning down the disk is useful - saves ~0.5W here. Powering down
> > SATA controller is even better -- should save ~1W.
> > 
> > Now, I guess the patch will need to be split to small pieces for
> > merge... I tried to rearrange it so that the documentation and hooks
> > go before stuff that needs the hooks, and before Kconfig enabler. If
> > it looks reasonably good, I'll split it into smaller pieces.
> 
> James had a number of objections to my original patch; you can read 
> them here:
> 
> https://lists.linux-foundation.org/pipermail/linux-pm/2008-March/016849.html

Very well. I see a basic problem here. For USB it is necessary that child
devices be suspended before anything higher up in the tree is suspended.
SATA seems to be able to power down a link while the device is not suspended.

In fact in true SCSI busses can be shared. So are we using the correct
approach?

	Regards
		Oliver
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