linux-kernel - Re: [PATCH v8 3/4] PM / sleep: Go direct

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Message-ID: <3377500.WbTIbyZKB6@vostro.rjw.lan>
Date:	Fri, 02 Oct 2015 15:42:57 +0200
From:	"Rafael J. Wysocki" <rjw@...ysocki.net>
To:	Ulf Hansson <ulf.hansson@...aro.org>
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>,
	Pavel Machek <pavel@....cz>
Subject: Re: [PATCH v8 3/4] PM / sleep: Go direct_complete if driver has no callbacks

On Friday, October 02, 2015 10:40:49 AM Ulf Hansson wrote:
> On 2 October 2015 at 10:10, Tomeu Vizoso <tomeu.vizoso@...labora.com> wrote:
> > On 2 October 2015 at 09:48, Ulf Hansson <ulf.hansson@...aro.org> wrote:
> >> On 2 October 2015 at 09:14, Tomeu Vizoso <tomeu.vizoso@...labora.com> 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.
> >>>
> >>> Signed-off-by: Tomeu Vizoso <tomeu.vizoso@...labora.com>
> >>> ---
> >>>
> >>> Changes in v8:
> >>> - Move no_pm_callbacks field into CONFIG_PM_SLEEP
> >>> - Call device_check_pm_callbacks only after a device is bound or unbound
> >>
> >> Devices that don't use a driver, will not get this feature for "free".
> >> I expect in those cases, they will have to call
> >> device_check_pm_callbacks() themselves, right?
> >
> > You are right, but wonder if we shouldn't go back to calling
> > device_check_pm_callbacks() from device_pm_add() and
> > dev_pm_domain_set() so they don't have to.
> 
> That seems reasonable to me, and I didn't quite understand why you
> decided to remove it. :-)

Right.

device_check_pm_callbacks() needs to be called on device registration too
(in case the device doesn't have a driver and doesn't use a PM domain) and
it won't hurt to call it in dev_pm_domain_set() either, although that likely
will be redundant in the majority of cases.

Thanks,
Rafael

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