On Wed, 2011-09-07 at 19:59 +0200, Hilman, Kevin wrote: > Tero Kristo <t-kristo@xxxxxx> writes: > > > Hi, > > > > On Sat, 2011-08-27 at 21:42 +0200, Alan Stern wrote: > >> On Sat, 27 Aug 2011, Santosh wrote: > >> > >> > On Saturday 27 August 2011 07:31 PM, Alan Stern wrote: > >> > > On Sat, 27 Aug 2011, Santosh wrote: > >> > > > >> > >> I might be wrong here, but after discussion with Govindraj on this > >> > >> issue, it seems there is a flaw in the way OMAP chain handler > >> > >> handling the child interrupts. > >> > >> > >> > >> On OMAP, we have special interrupt wakeup source at PRCM level and > >> > >> many devices can trigger wakeup from low power via this common > >> > >> interrupt source. The common interrupt source upon wakeup from low > >> > >> power state, decodes the source of interrupt and based on that > >> > >> source, calls the respective device ISR directly. > >> > >> > >> > >> The issue I see here is, the ISR on _a_ device (UART in this case) > >> > >> is happening even before UART resume and DPM resume has been completed. > >> > >> If this is the case, then it is surely asking for trouble. Because not > >> > >> just clocks, but even driver state machine is already in suspend state > >> > >> when the ISR is called. > >> > > > >> > > If the driver state machine is in the suspend state when the ISR is > >> > > called, then the ISR should realize it is handling a wakeup event > >> > > instead of a normal I/O event. All it needs to do is turn off the > >> > > interrupt source; the event itself will be taken care of during the > >> > > device's resume callback. > >> > > > >> > Good point but the ISR is called as a function call and not real > >> > hardware event so no need to turn-off the source in the child > >> > ISR. Parent ISR will clear the source anyways. > >> > > >> > But the intention here is to record the event for the child. > >> > >> In that case the ISR only has to record the event. > >> > >> > I mean for UART wakeup, the received character should be > >> > extracted. If not done, UART will loose that character because > >> > the event is lost. So not sure how the event will be taken > >> > care during resume callback. Could you elaborate bit more on > >> > last comment please? > >> > >> The resume callback routine must check to see if an event was recorded. > >> If one was, the routine must see whether a character was received while > >> the system was asleep and extract the character from the UART. (It > >> probably won't hurt to do this even if an event wasn't recorded.) > >> > >> Alan Stern > >> > > > > After thinking about this problem and looking at possible ways to fix > > it, I am planning to change the PRCM chain handler to be a driver, which > > gets suspended along with the rest of the system. This means the PRCM > > interrupt would get disabled also during this time, and it would be > > enabled in the driver->complete() call, which should happen after rest > > of the drivers have been able to enable their PM runtime in the > > driver->resume() call chain. Do you see any problems with this approach? > > How will the system wakeup from retention or off-mode if the PRCM IRQ is > disabled? This is actually some sort of an issue with retention if we disable PRCM irq completely, off works purely with wakeup signals as we come out of reset. Anyway, I did some experimentation with this, and OMAP3 is able to wake up if we leave WKUP irq up, but disable IO chain irq. IO chain events seem to trigger a WKUP event also always, we just postpone the processing of IO chain until later. I had to also split the wakeup clearing for OMAP3 into 2 parts, one part handles wakeups and another IO chain. Currently both IO chain and WKUP are acked by the same handler. > Besides that, I don't like this approach because it leaves a rather long > window during which no PRCM-triggered wakeup events can happen. This is > not good since we also want potential wakeup events that happen *during* > system suspend to be able to cancel the suspend. This should also be taken care of by the approach described above. > > > The only issue I am seeing myself is if some driver decides to do > > resume() in the complete() pm-op and potentially screwing the ordering > > here... > > Personally, I think Alan's approach is the only scalable approach. This > has to be handled by the drivers. > > If the driver's ISR does a pm_runtime_get_sync() and it fails (in this > case, with -EACCESS since runtime PM is disabled), the driver should > handle that handle as Alan described above. Yea I think this probably needs to be done anyway, at least on some cases. The PRCM chain handler approach might be able to solve most of the problems though. I think I will post what I have anyway for comments hopefully later today, so you can have a look and say what you think. -Tero Texas Instruments Oy, Tekniikantie 12, 02150 Espoo. Y-tunnus: 0115040-6. 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