linux-kernel - Re: [linux-usb-devel] error to be returned while suspended

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Date:	Thu, 5 Oct 2006 12:21:45 -0400 (EDT)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Oliver Neukum <oliver@...kum.org>
cc:	Pavel Machek <pavel@....cz>, <linux-kernel@...r.kernel.org>,
	<linux-usb-devel@...ts.sourceforge.net>
Subject: Re: [linux-usb-devel] error to be returned while suspended

On Thu, 5 Oct 2006, Oliver Neukum wrote:

> > > > If you are talking runtime suspend, you should probably just wake the
> > > > device up on first access.
> > > 
> > > Do you really think a device driver should override an explicitely
> > > selected power state?
> > 
> > (So we are talking runtime suspend?)
> 
> Yes. Otherwise the patch would have been ready two days ago.
> But if I am implenting this, I'll do a full implementation.
> 
> > No, I do not know what the right interface is. I started to suspect
> > that drivers should suspend/resume devices automatically, without
> > userland help. Maybe having autosuspend_timeout in sysfs is enough.
> 
> If you do this at kernel level, you'll screw up any demon implementing
> a power policy to stay within the budget.

Currently we don't have any userspace APIs for such a daemon to use.  The 
only existing API is deprecated and will go away soon.

Current thinking is that a driver will suspend its device whenever the 
device isn't in use.  With usblp, that would be whenever the device file 
isn't open.  See the example code in usb-skeleton.c.

Alan Stern

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