linux-kernel - Re: [linux-pm] [PATCH 2/4] PM / Loss: power loss management

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Message-ID: <Pine.LNX.4.44L0.1105191021220.1900-100000@iolanthe.rowland.org>
Date:	Thu, 19 May 2011 10:25:12 -0400 (EDT)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Davide Ciminaghi <ciminaghi@...dd.com>
cc:	"Rafael J. Wysocki" <rjw@...k.pl>,
	<davinci-linux-open-source@...ux.davincidsp.com>,
	Greg Kroah-Hartman <gregkh@...e.de>,
	<linux-kernel@...r.kernel.org>,
	Raffaele Recalcati <raffaele.recalcati@...cino.it>,
	<linux-pm@...ts.linux-foundation.org>,
	Raffaele Recalcati <lamiaposta71@...il.com>
Subject: Re: [linux-pm] [PATCH 2/4] PM / Loss: power loss management

On Thu, 19 May 2011, Davide Ciminaghi wrote:

> I'm not completely sure about this. What we wanted to do was to avoid powering
> down the mmc while it is physically writing data into its internal memory.
> If we force a sync when the power loss warning event warning happens,
> it is very difficult to be able to guarantee that all buffered data will be 
> written before power actually dies. So we preferred to follow another strategy:
> let the mmc finish any running write operation, and then stop its request 
> queue. If power really goes down, then we hope that the file system journal 
> will fix things on next boot (yes, some data could get lost, but the fs should
> still be mountable). On the other hand, if power resumes, nothing bad should 
> happen for user space processes.

You could consider a totally different approach.

Each platform will have a different set of high-power devices it wants
to turn off when a power-loss warning occurs.  So instead of changing
the core PM interface, you could add a new "power_loss" notifier list.  
Only the most critical drivers would need to listen for notifications, 
and this could be different drivers on different platforms.

Alan Stern

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