linux-kernel - Re: [PATCH 2/3] [SCSI]: runtime resume parent for child's system-resume

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Date:	Wed, 14 Dec 2011 11:51:43 -0500 (EST)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Lin Ming <ming.m.lin@...el.com>
cc:	Jeff Garzik <jgarzik@...ox.com>,
	James Bottomley <JBottomley@...allels.com>,
	Tejun Heo <tj@...nel.org>, <linux-kernel@...r.kernel.org>,
	<linux-ide@...r.kernel.org>, <linux-scsi@...r.kernel.org>,
	<linux-pm@...r.kernel.org>
Subject: Re: [PATCH 2/3] [SCSI]: runtime resume parent for child's system-resume

On Wed, 14 Dec 2011, Lin Ming wrote:

> On Wed, Dec 14, 2011 at 11:18 AM, Lin Ming <ming.m.lin@...el.com> wrote:
> > [Patch description from Alan Stern]
> >
> > If a child device was runtime-suspended when a system suspend began,
> > then there will be nothing to prevent its parent from
> > runtime-suspending as soon as it is woken up during the system resume.
> > Then when the time comes to resume the child, the resume will fail
> > because the parent is already back at low power.
> >
> > On the other hand, there are some devices which should remain at low
> > power across an entire suspend-resume cycle.  The details depend on the
> > device and the platform.
> >
> > This suggests that the PM core is not the right place to solve the
> > problem.  One possible solution is for the subsystem or device driver
> > to call pm_runtime_get_sync(dev->parent) at the start of the
> > system-resume procedure and pm_runtime_put_sync(dev->parent) at the
> > end.
> >
> > Signed-off-by: Lin Ming <ming.m.lin@...el.com>
> 
> Hi Alan,
> 
> May I add your SOB?

You can add: Acked-by: Alan Stern <stern@...land.harvard.edu>

Did you test this?  Does it do what you want?

Alan Stern

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