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? 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. > 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. Kevin -- To unsubscribe from this list: send the line "unsubscribe linux-omap" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
