linux-kernel - Re: [RFC][PATCH 2/3] PM / sleep: Mechanism to avoid resuming runtime-suspended devices unnecessarily

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Date:	Mon, 19 May 2014 22:13:02 +0200
From:	"Rafael J. Wysocki" <rjw@...ysocki.net>
To:	Alan Stern <stern@...land.harvard.edu>
Cc:	Jacob Pan <jacob.jun.pan@...ux.intel.com>,
	Linux PM list <linux-pm@...r.kernel.org>,
	ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
	Aaron Lu <aaron.lu@...el.com>,
	Mika Westerberg <mika.westerberg@...ux.intel.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Kevin Hilman <khilman@...aro.org>,
	Ulf Hansson <ulf.hansson@...aro.org>
Subject: Re: [RFC][PATCH 2/3] PM / sleep: Mechanism to avoid resuming runtime-suspended devices unnecessarily

On Monday, May 19, 2014 03:53:58 PM Alan Stern wrote:
> On Mon, 19 May 2014, Jacob Pan wrote:
> 
> > > Wouldn't that go a bit too far?  It seems to be based on the
> > > assumption that all devices having no ->prepare() callback can be
> > > safely left in runtime suspend over a system suspend/resume cycle,
> > > but is that assumption actually satisfied for all such devices?
> > > 
> > yes, I agree it is risky though i don't see problems with my limited
> > testing. But on the other side, it is too strict.
> > I also tried adding .prepare( return 1;) to usb_ep_device_type pm ops,
> > that didn't work either. The reason is that ep devices don't support
> > runtime pm (disable_depth > 0). I think in this case ignore_children
> > flag should be the right indicator to ignore pm_runtime_suspended()?
> 
> Maybe it would be better to add a new flag that means "This is a 
> virtual device and the PM core can ignore it completely".

I like that idea. :-)

Rafael

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