Re: System sleep vs. runtime PM

Alan Stern
2009-12-03T15:25:30Z

On Thu, 3 Dec 2009, Oliver Neukum wrote:

> An evil thought, do we have devices that will always request remote wakeup,
> without an option to switch it off? What about OTG?

I don't know of any such devices. USB OTG will depend on the
controller design, but I would be surprised to find a controller that
didn't let you turn off wakeup-IRQ generation.

> > There's yet another issue to discuss. Suppose a device is
> > runtime-suspended when a system sleep starts. When the system wakes
> > up, should the device be runtime-resumed? (Assume that the wakeup
> > settings don't differ; otherwise it has to be.)
>
> That depends on how sure we are to never drop a remote wakeup,
> not even if requests race or for any other reason. And we must always
> know what woke us up.

This is a complicated question and I will discuss it at greater length
in another email.

However, I don't see any reason to know what woke us up. All we really
need to know is what devices have wakeup requests outstanding when the
system resume is finished. It doesn't matter which request came first
(presumably that was the one which woke us up).

Alan Stern