Re: [linux-pm] pm loss development

From: Rafael J. Wysocki
Date: Tue May 17 2011 - 19:06:21 EST

On Saturday, May 14, 2011, Raffaele Recalcati wrote:
> On Sat, May 14, 2011 at 8:53 PM, Oliver Neukum <oliver@xxxxxxxxxx> 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.

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