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

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Date:	Wed, 29 Jul 2009 18:53:45 -0400
From:	Arnaud Faucher <arnaud.faucher@...il.com>
To:	Dmitry Torokhov <dmitry.torokhov@...il.com>
Cc:	"Rafael J. Wysocki" <rjw@...k.pl>,
	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 Wed, Jul 29, 2009 at 14:03 -0700, 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.
> 

As of today, acer_platform_freeze() does not stop/reset any device, so,
I agree with Rafael that for acer-wmi, .thaw() can be skipped. I had
also tested this configuration and it was working like the non-patched
code.

Carlos, do you think that any acer-specific hardware could be switched
off or reset inside acer_platform_freeze() ? If this was the case, we
would have to wire .thaw()...

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