Re: patch to autosuspend mice

Am Mittwoch, 31. Januar 2007 20:25 schrieb Alan Stern:
> > How do I find out whether the device is idle?
> > The mouse is not idle if it has been moved (or buttons clicked)
> > To find out whether it has been moved the device must not be suspended.
> > At which point in time then should I check? Are you saying that the
> > timer should be started and suspend() should fail if the devices hasn't
> > been idle?
> 
> Logically speaking, the computer doesn't and can't know if the device is 
> currently idle.  After all, it takes several milliseconds for the HID 
> reports indicating any activity to be transferred from the device to the 
> computer, so the computer's knowledge is always at least a little bit out 
> of date.

Yes, this race condition is unavoidable.

> So you shouldn't base any decisions on whether the device is currently
> idle.  Instead, you have to check whether the device has been idle for a
> sufficiently long time.  That's what the timer is for: You restart the

Yes, that's the way I currently do it.

> timer whenever there is any activity, and when the timer expires you know
> the device has been idle long enough that you should suspend it.  That's
> exactly how the autosuspend infrastructure works.

This would call mod_timer() for every completed in-URB. Are you
sure this is better than an approach maintaining a periodical timer
and check for IO in the meantime?

	Regards
		Oliver

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