* Arve Hjønnevåg <arve@xxxxxxxxxxx> [100505 21:11]: > On Wed, May 5, 2010 at 5:05 PM, Tony Lindgren <tony@xxxxxxxxxxx> wrote: > > * Brian Swetland <swetland@xxxxxxxxxx> [100505 16:51]: > >> On Wed, May 5, 2010 at 4:47 PM, Tony Lindgren <tony@xxxxxxxxxxx> wrote: > >> > * Brian Swetland <swetland@xxxxxxxxxx> [100505 14:34]: > >> >> On Wed, May 5, 2010 at 2:12 PM, Alan Stern <stern@xxxxxxxxxxxxxxxxxxx> wrote: > >> >> >> > >> >> >> Oh, like tell the modem that user mode has handled the ring event and > >> >> >> its ok to un-block? > >> >> > > >> >> > No, that's not how it works. It would go like this: > >> >> > > >> >> > The modem IRQ handler queues its event to the input subsystem. > >> >> > As it does so the input subsystem enables a suspend blocker, > >> >> > causing the system to stay awake after the IRQ is done. > >> > > >> > How about instead the modem driver fails to suspend until it's done? > >> > > >> > Each driver could have a suspend_policy sysfs entry with options such > >> > as [ forced | safe ]. The default would be forced. Forced would > >> > be the current behaviour, while safe would refuse suspend until the > >> > driver is done processing. > >> > > >> >> > The user program enables its own suspend blocker before reading > >> >> > the input queue. When the queue is empty, the input subsystem > >> >> > releases its suspend blocker. > >> > > >> > And also the input layer could refuse to suspend until it's done. > >> > > >> >> > When the user program finishes processing the event, it > >> >> > releases its suspend blocker. Now the system can go back to > >> >> > sleep. > >> > > >> > And here the user space just tries to suspend again when it's done? > >> > It's not like you're trying to suspend all the time, so it should be > >> > OK to retry a few times. > >> > >> We actually are trying to suspend all the time -- that's our basic > >> model -- suspend whenever we can when something doesn't prevent it. > > > > Maybe that state could be kept in some userspace suspend policy manager? > > > >> >> > At no point does the user program have to communicate anything to the > >> >> > modem driver, and at no point does it have to do anything out of the > >> >> > ordinary except to enable and disable a suspend blocker. > >> >> > >> >> Exactly -- and you can use the same style of overlapping suspend > >> >> blockers with other drivers than input, if the input interface is not > >> >> suitable for the particular interaction. > >> > > >> > Would the suspend blockers still be needed somewhere in the example > >> > above? > >> > >> How often would we retry suspending? > > > > Well based on some timer, the same way the screen blanks? Or five > > seconds of no audio play? So if the suspend fails, then reset whatever > > userspace suspend policy timers. > > > >> If we fail to suspend, don't we have to resume all the drivers that > >> suspended before the one that failed? (Maybe I'm mistaken here) > > > > Sure, but I guess that should be a rare event that only happens when > > you try to suspend and something interrupts the suspend. > > > > This is not a rare event. For example, the matrix keypad driver blocks > suspend when a key is down so it can scan the matrix. Sure, but how many times per day are you suspending? > >> With the suspend block model we know the moment we're capable of > >> suspending and then can suspend at that moment. Continually trying to > >> suspend seems like it'd be inefficient power-wise (we're going to be > >> doing a lot more work as we try to suspend over and over, or we're > >> going to retry after a timeout and spend extra time not suspended). > >> > >> We can often spend minutes (possibly many) at a time preventing > >> suspend when the system is doing work that would be interrupted by a > >> full suspend. > > > > Maybe you a userspace suspend policy manager would do the trick if > > it knows when the screen is blanked and no audio has been played for > > five seconds etc? > > > > If user space has to initiate every suspend attempt, then you are > forcing it to poll whenever a driver needs to block suspend. Hmm I don't follow you. If the userspace policy daemon timer times out, the device suspends. If the device does not suspend because of a blocking driver, then the timers get reset and you try again based on some event such as when the screen blanks. Regards, Tony -- To unsubscribe from this list: send the line "unsubscribe linux-doc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html