From: "Rafael J. Wysocki" <rjw@sisk.pl>
To: markgross@thegnar.org
Subject: Re: [linux-pm] pm loss development
Date: Wed, 18 May 2011 21:43:13 +0200
User-Agent: KMail/1.13.6 (Linux/2.6.39-rc7+; KDE/4.6.0; x86_64; ; )
Cc: Raffaele Recalcati <lamiaposta71@gmail.com>,
        linux-pm@lists.linux-foundation.org,
        davinci-linux-open-source@linux.davincidsp.com,
        linux-kernel@vger.kernel.org
References: <1305220265-9020-1-git-send-email-lamiaposta71@gmail.com> <201105180107.58078.rjw@sisk.pl> <20110518031203.GA3640@gvim.org>
In-Reply-To: <20110518031203.GA3640@gvim.org>
MIME-Version: 1.0
Content-Type: Text/Plain;
  charset="iso-8859-1"
Content-Transfer-Encoding: 7bit
Message-Id: <201105182143.13237.rjw@sisk.pl>
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 2724
Lines: 57

On Wednesday, May 18, 2011, mark gross wrote:
> On Wed, May 18, 2011 at 01:07:57AM +0200, Rafael J. Wysocki wrote:
> > On Saturday, May 14, 2011, mark gross wrote:
> > > On Fri, May 13, 2011 at 06:54:57PM +0200, Rafael J. Wysocki wrote:
> > > > On Friday, May 13, 2011, Raffaele Recalcati wrote:
> > > > > Hi Rafael,
> > > > > 
> > > > > 2011/5/12 Rafael J. Wysocki <rjw@sisk.pl>:
> > > > > > 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?
> > > > > 
> > > > > Take a quick look at Documentation/power/loss.txt  paragrpah "2.4
> > > > > Power loss policies".
> > > > > You can decide what can be powered off.
> > > > 
> > > > I read the patches.  My question was about the general idea of who should
> > > > be responsible of making these decisions.
> > > 
> > > I would expect the system integrator would based on the application the
> > > device is getting deployed into.
> > > 
> > > A generic opportunistic policy for peripherals that are stateless and can
> > > be trivially power gated off/on from an ISR could be a default but, for
> > > peripherals that need to do some processing (like waiting on an eMMC DMA
> > > to complete) can take time to power down into a safe state.
> > 
> > What do you mean by safe state?
> >
> I need to get more details on this but I assume its a state where the
> meta data of the file system is committed to the emmc before lights go
> off such that when power is reapplied that the damage isn't too big. 

I don't think you can guarantee that the metadata won't be damaged
without notifying the filesystem of the event (and making it react
appropriately).

> I've also heard some talk of sim card corruption risks but, I don't have
> first hand info on that.

Well, I guess that might be prevented by the driver alone.

Thanks,
Rafael
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/