linux-kernel - Re: [PATCH 1/1] acer-wmi: switch driver to dev_pm

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Message-Id: <200907300127.19358.rjw@sisk.pl>
Date:	Thu, 30 Jul 2009 01:27:18 +0200
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Dmitry Torokhov <dmitry.torokhov@...il.com>
Cc:	Arnaud Faucher <arnaud.faucher@...il.com>,
	Carlos Corbacho <carlos@...angeworlds.co.uk>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Frans Pop <elendil@...net.nl>,
	Manuel Lauss <manuel.lauss@...il.com>,
	Erik Ekman <erik@...o.se>,
	Mark Brown <broonie@...nsource.wolfsonmicro.com>
Subject: Re: [PATCH 1/1] acer-wmi: switch driver to dev_pm_ops

On Wednesday 29 July 2009, Dmitry Torokhov wrote:
> On Wed, Jul 29, 2009 at 10:49:46PM +0200, Rafael J. Wysocki wrote:
> > On Wednesday 29 July 2009, Arnaud Faucher wrote:
> > 
> > > As per the pm.h documentation .thaw is called after RAM image has been
> > > created, in order to restore hardware state in case RAM image failed and
> > > the system cannot power off.
> > 
> > That's not correct (please see above).  .thaw() is called after creating the
> > image in case .freeze() has changed the state of the device.  This often is not
> > necessary, though, so .thaw() may be skipped in many cases.  Of course, you
> > should know exactly what you're doing.
> > 
> 
> Umm, but thaw() _is_ called in case of hibernate failure:
> 
>         case PM_EVENT_THAW:
>         case PM_EVENT_RECOVER:
>                 if (ops->thaw) {
>                         error = ops->thaw(dev);
>                         suspend_report_result(ops->thaw, error);
>                 }
>                 break;
> 
> so I don't believe you can easily skip thaw() if you have freeze() that
> stops/resets device.

_RECOVER means "image creation failed or unable to run the image kernel", so
from the devices' point of view it's the same as _THAW.

Still, if your .freeze() modifies the device's registers, then most likely
.thaw() _is_ necessary.

Best,
Rafael
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