linux-kernel - Re: [PATCH 2/3] scsi: add hooks for host runtime power management

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Date:	Thu, 3 Nov 2011 12:08:53 -0400 (EDT)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Tejun Heo <tj@...nel.org>
cc:	Lin Ming <ming.m.lin@...el.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-ide@...r.kernel.org" <linux-ide@...r.kernel.org>,
	"linux-scsi@...r.kernel.org" <linux-scsi@...r.kernel.org>,
	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
	Jeff Garzik <jgarzik@...ox.com>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	James Bottomley <JBottomley@...allels.com>,
	"Huang, Ying" <ying.huang@...el.com>,
	"Zhang, Rui" <rui.zhang@...el.com>
Subject: Re: [PATCH 2/3] scsi: add hooks for host runtime power management

On Thu, 3 Nov 2011, Tejun Heo wrote:

> Hello,
> 
> On Thu, Nov 3, 2011 at 8:39 AM, Alan Stern <stern@...land.harvard.edu> wrote:
> >> I don't know. I haven't really thought about it but as it's currently
> >> designed, I don't think it'll be possible to avoid going through EH to
> >> put ATA ports into suspend mode.
> >
> > Why not?
> 
> It's just how things are designed now.  There's no reason why it's
> fundamentally impossible but going around that would require some
> amount of hackery or preferably re-design.  Synchronization against
> command processing, interrupts and all are built around EH.

Then it sounds like the best idea is something like what Ming proposed 
earlier: Have the error handler make some sort of test to determine 
whether it has been invoked for suspend/resume handling, and skip the 
runtime-PM calls on the host if it has.

This new test, whatever it is, should apply both to system suspend and 
runtime suspend.  By the way, what would happen if a system suspend 
occurred while the ATA port was already runtime-suspended?

Alan Stern

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