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

Alan Stern
2006-10-05T16:21:51Z

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