On Fri, 25 Nov 2005, David Brownell wrote:

> 
> > > > > When the infrastructure is in place, it will automatically take care 
> > > > > of 
> > > > > suspending the device once all the interfaces are suspended.  For 
> > > > > now, 
> > > > > however, that's your responsibility.
> > > 
> > > I'd say it differently:  For now don't try that at all.  Because in 
> > > addition
> > > to an autosuspend mechanism being missing, so is autoresume.
> > 
> > That's not quite true.  usbcore is aware of remote wakeup signals and will
> > automatically take care of resuming the device and all its interfaces.  
> > Remember, though, that everything you do will be experimental and subject
> > to change once the runtime PM infrastructure is ready.
> 
> By "autoresume" I meant at the level of automatically resuming an interface
> (and hence potentially device) that's been "autosuspended" and which does
> not support remote wakeup.  One example would be a usb-storage device; they
> rarely support remote wakeup.  For something like a USB mouse, you're right
> that remote wakeup will normally suffice ... it wouldn't need autoresume.

That's correct.  If the device does not support remote wakeup, or if Ben 
wants to resume it at a time when it hasn't sent a wakeup signal, then the 
driver would have to call dpm_runtime_resume.

Currently it suffices to resume just the device and not the interfaces,
because usbcore automatically resumes all the interfaces when a device is
resumed.  However it's not guaranteed that this behavior will persist --
in the future we may want to change things so that this "autoresume the
interfaces" happens only in response to remote wakeups.

Alan Stern



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