Re: [update] Re: [PATCH] PM: Make it possible to avoid wakeup eventsfrom being lost

From: Alan Stern
Date: Wed Jun 30 2010 - 14:00:50 EST

On Mon, 28 Jun 2010, Rafael J. Wysocki wrote:

> +/*
> + * The functions below use the observation that each wakeup event starts a
> + * period in which the system should not be suspended. The moment this period
> + * will end depends on how the wakeup event is going to be processed after being
> + * detected and all of the possible cases can be divided into two distinct
> + * groups.
> + *
> + * First, a wakeup event may be detected by the same functional unit that will
> + * carry out the entire processing of it and possibly will pass it to user space
> + * for further processing. In that case the functional unit that has detected
> + * the event may later "close" the "no suspend" period associated with it
> + * directly as soon as it has been dealt with. The pair of pm_stay_awake() and
> + * pm_relax(), balanced with each other, is supposed to be used in such
> + * situations.
> + *
> + * Second, a wakeup event may be detected by one functional unit and processed
> + * by another one. In that case the unit that has detected it cannot really
> + * "close" the "no suspend" period associated with it, unless it knows in
> + * advance what's going to happen to the event during processing. This
> + * knowledge, however, may not be available to it, so it can simply specify time
> + * to wait before the system can be suspended and pass it as the second
> + * argument of pm_wakeup_event().
> + */

Since there's no longer any way to cancel a call to pm_wakeup_event()
or close the "no suspend" period early, there is no need to use
dynamically-allocated delayed_work structures. You can make do with a
single static timer; always keep it set to expire at the latest time
passed to pm_wakeup_event().

Alan Stern

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