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

From: Alan Stern
Date: Thu May 19 2011 - 10:25:18 EST

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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