linux-kernel - Re: [PATCH 2/2] thermal: rcar_thermal: use pm_runtime_put

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Date:	Thu, 12 Nov 2015 09:04:09 +0100
From:	Ulf Hansson <ulf.hansson@...aro.org>
To:	"Rafael J. Wysocki" <rjw@...ysocki.net>
Cc:	Geert Uytterhoeven <geert@...ux-m68k.org>,
	Kuninori Morimoto <kuninori.morimoto.gx@...esas.com>,
	Zhang Rui <rui.zhang@...el.com>,
	Eduardo Valentin <edubezval@...il.com>,
	Linux-SH <linux-sh@...r.kernel.org>,
	Linux-Kernel <linux-kernel@...r.kernel.org>,
	Linux PM list <linux-pm@...r.kernel.org>,
	Cao Minh Hiep <cm-hiep@...so.co.jp>,
	Dung：人ソ <nv-dung@...so.co.jp>,
	Alan Stern <stern@...land.harvard.edu>
Subject: Re: [PATCH 2/2] thermal: rcar_thermal: use pm_runtime_put_sync()

On 12 November 2015 at 02:06, Rafael J. Wysocki <rjw@...ysocki.net> wrote:
> On Wednesday, November 11, 2015 12:03:52 PM Ulf Hansson wrote:
>> On 11 November 2015 at 00:57, Rafael J. Wysocki <rjw@...ysocki.net> wrote:
>> > On Tuesday, November 10, 2015 02:00:38 PM Ulf Hansson wrote:
>> >> +Rafael, Alan
>> >>
>> >> On 10 November 2015 at 11:10, Geert Uytterhoeven <geert@...ux-m68k.org> wrote:
>> >> > Hi Ulf,
>> >> >
>> >
>> > [cut]
>> >
>> >> >>
>> >> >> The problem is that the runtime PM status of the device isn't
>> >> >> correctly updated at ->remove(). The effect is that the the
>> >> >> pm_runtime_get_sync() in ->probe() at re-bind will *not* trigger the
>> >> >> ->runtime_resume() callbacks to be invoked, as the runtime PM core
>> >> >> believes the device is already runtime resumed.
>> >> >
>> >> > So that's where it should be fixed?
>> >>
>> >> That would be a more generic approach, although I am not sure how the
>> >> driver/PM core should be able to take the correct decision in this
>> >> phase. Devices may be runtime PM managed also without a driver bound.
>> >>
>> >> Perhaps when __device_release_driver() finds a bounded driver for the
>> >> device, it could after all actions been performed to unbind the
>> >> driver, check if runtime PM is enabled. If it isn't, it could set the
>> >> runtime PM status to suspended!?
>> >>
>> >> I have no idea if that would introduce other issues as it would kind
>> >> of force the runtime PM status of the device to suspend, without
>> >> actually knowing if it's the correct thing to do.
>> >
>> > IMO, that needs to depend on the bus type.  If the bus type has a way
>> > to manage PM for devices without drivers, it should be allowed to do so.
>>
>> By following my suggestion above, we would allow the bus/driver's
>> ->remove() to manage whether runtime PM should be enabled/disabled for
>> the device, before __device_release_driver() checks that.
>> Don't you think that the driver core could rely on that information?
>>
>> I realize that it would be a kind of policy decision for runtime PM,
>> but it's quite similar as when register/unregister devices when we set
>> the runtime PM status to suspended.
>
> OK
>
> If we did that, all devices that had just been unbound from their drivers
> and had runtime PM disabled after that would be set to "suspended" by the
> core, right?

Yes, that's the idea. I will send a patch we can test.

>
> If that helps, I don't really have objections.
>

Thanks!

Kind regards
Uffe
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