linux-kernel - Re: [PATCH v5 1/2] PM / sleep: Go direct

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Message-ID: <5808910.FQ4CPUCAtb@vostro.rjw.lan>
Date:	Mon, 05 Oct 2015 15:29:59 +0200
From:	"Rafael J. Wysocki" <rjw@...ysocki.net>
To:	Pavel Machek <pavel@....cz>
Cc:	Tomeu Vizoso <tomeu.vizoso@...labora.com>,
	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
	Alan Stern <stern@...land.harvard.edu>,
	martyn.welch@...labora.co.uk,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Len Brown <len.brown@...el.com>,
	Kevin Hilman <khilman@...nel.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Ulf Hansson <ulf.hansson@...aro.org>
Subject: Re: [PATCH v5 1/2] PM / sleep: Go direct_complete if driver has no callbacks

On Monday, October 05, 2015 11:07:27 AM Pavel Machek wrote:
> On Mon 2015-10-05 10:25:45, Tomeu Vizoso wrote:
> > On 4 October 2015 at 17:16, Pavel Machek <pavel@....cz> wrote:
> > > On Tue 2015-09-29 14:29:19, Tomeu Vizoso wrote:
> > >> If a suitable prepare callback cannot be found for a given device and
> > >> its driver has no PM callbacks at all, assume that it can go direct to
> > >> complete when the system goes to sleep.
> > >>
> > >> The reason for this is that there's lots of devices in a system that do
> > >> no PM at all and there's no reason for them to prevent their ancestors
> > >> to do direct_complete if they can support it.
> > >
> > > Dunno. This sounds like asking for trouble. Even if most devices can handle
> > > this, is not this bound to introduce some bugs?
> > 
> > Hi Pavel,
> > 
> > in which situations do you think that this could be problematic?
> 
> Well.. driver with no PM callbacks probably works "by accident",

How exactly?

Do you have at least one example of that?

Thanks,
Rafael

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