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 -- 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
