linux-kernel - Re: [linux-pm] pm loss development

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Message-Id: <201105180106.57147.rjw@sisk.pl>
Date:	Wed, 18 May 2011 01:06:56 +0200
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Raffaele Recalcati <lamiaposta71@...il.com>
Cc:	Oliver Neukum <oliver@...kum.org>,
	linux-pm@...ts.linux-foundation.org,
	davinci-linux-open-source@...ux.davincidsp.com,
	linux-kernel@...r.kernel.org
Subject: Re: [linux-pm] pm loss development

On Saturday, May 14, 2011, Raffaele Recalcati wrote:
> On Sat, May 14, 2011 at 8:53 PM, Oliver Neukum <oliver@...kum.org> wrote:
> > Am Donnerstag, 12. Mai 2011, 21:27:44 schrieb Rafael J. Wysocki:
> >> On Thursday, May 12, 2011, Raffaele Recalcati wrote:
> >> > What happen normally in runtime pm implementation is that every devices
> >> > are switched off and are enabled only when needed.
> >> > In our case instead we have a completely functional embedded system and,
> >> > when an asyncrhonous event appear, we have only some tens milliseconds
> >> > before the actual power failure takes place.
> >> > This patchset add a support in order to switch off not vital part of the system,
> >> > in order to allow the board to survive longer.
> >> > This allow the possibility to save important data.
> >>
> >> OK, so first, who decides what parts of the system are vital and what aren't?
> >
> > If you know that power is failing in a few miliseconds, only stuff that can lead to data
> > corruption is vital. In that timeframe you can't even flush buffers.
> 
> Remember that if you switch off some peripherals this timeframe
> becomes longer, so maybe you have enough time to sync some storage
> devices.

However, switching off peripherals _also_ takes time.  So, it may be more
useful to take care of the stuff leading to data corruption along with the
switching off peripherals.

Thanks,
Rafael
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