Re: [PATCH] usb: Add support for runtime power management of the hcd

Rafael J. Wysocki
2009-11-11T22:24:57Z

On Wednesday 11 November 2009, Alan Stern wrote:
> On Wed, 11 Nov 2009, Oliver Neukum wrote:
>
> > Am Mittwoch, 11. November 2009 18:08:17 schrieb Alan Stern:
> > > On Wed, 11 Nov 2009, Oliver Neukum wrote:
> >
> > > > That seems to be a bit harsh. If you do not specify that a device be
> > > > able to wake the whole system, why would it be good for a request
> > > > coming from it to abort a system sleep transition?
> > >
> > > The way you specify that a device be able to wake the whole system is
> > > by enabling its remote wakeup attribute. If this attribute is not
> > > enabled then the device will not send remote wakeup requests, so the
> > > scenario described above will not occur -- no IRQ will be generated.
> >
> > But what happens if a driver has requested remote wakeup requests
> > to do runtime power management?
>
> The driver mustn't tell the device to send remote wakeup requests if
> the remote wakeup attribute isn't set. If this means it can't do
> effective runtime PM, then so be it.
>
> Now, this does raise another point, which has been mentioned before.
> To wit: devices really ought to have _two_ remote-wakeup attributes,
> one for runtime PM and one for system sleep.

Yes, they do and there's another reason. Namely, there apparently are
devices which can wake up the system from a sleep state and that are
unable to generate runtime wakeup events.

> But that would introduce yet more complexity and opportunities for
> confusion.

Nevertheless.

Thanks,
Rafael
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