NeilBrown <neilb@xxxxxxx> writes: > On Fri, 10 Aug 2012 11:49:27 -0700 Kevin Hilman <khilman@xxxxxx> wrote: > >> Hello, >> >> In doing some automated testing of suspend/resume I noticed that >> repeated attempts to suspend and resume via RTC wakeup fail on >> 3530/Beagle and 3730/Beagle-xM, but work fine on 3430/n900, 3530/Overo, >> 3730/OveroSTORM and 4430/Panda. >> >> When RTC wakeup fails, a UART wakeup will work, and in the logs, you'll >> see this: >> >> [ 316.036132] twl: i2c_read failed to transfer all messages >> [ 316.036163] twl4030: I2C error -13 reading PIH ISR >> >> My guess about what might be happening is that very late in the suspend >> process (during the noirq hooks), a PMIC interrupt fires, but by this >> time the I2C driver is runtime suspended (and clock gated.) Since >> runtime PM is disabled at this point, I2C reads fail, so the twl4030 IRQ >> driver cannot talk over I2C to the PMIC to determine the interrupt >> source. > > This area seems to be rife with opportunity for bugs. I wrote about some of > it here: https://lwn.net/Articles/482345/ Yeah, that was a great article. > I don't know that I saw quite what you are seeing though. > > If a PMIC interrupt fires during the noirq phase, the interrupt handler > shouldn't be run (it isn't marked NOSUSPEND). However there is probably room > for a race between the 'suspend' phase and the 'noirq' phase. > > When the suspend processing handles the I2C device, the last thing that > __device_suspend does is > > __pm_runtime_disable(dev, false); > > which will freeze the current runtime_pm state of the I2C device. If it is > off, it stays off. If on, it stays on. Correct. > As the noirq phase hasn't been entered yet an interrupt from the PMIC could > still be handled. If it is, you get exactly the error you see. Right, this is what I suspect is happening. I just haven't had the time to confirm and/or fix. > I'm not convinced that the __pm_runtime_disable call is correct. It think we > need to stop async runtime_suspends, but we don't need to stop sync > runtime_resumes. So just a pm_runtime_get should be enough. But there is > possibly an important point I am missing. Yes, I went back and forth with Rafael on the interactions between system PM and runtime PM and he pursuaded me that there were a handful of reasons that system PM needed to block runtime PM transitions. I don't recall what they are at the moment (my brain is already being pre-flushed in preparation for some time off.) > However if my analysis is correct, then this can be 'fixed' by changing the > omap i2c suspend routine to do a pm_runtime_get, and the resume routine to do > a pm_runtime_put. The I2C will still be put to sleep during suspend by the > noirq suspend handler, but we will be sure of it being awake during the > crucial suspend and resume transition. Hmm, that's a good idea. Hopefully someone can give it a try before I get back from vacation. :) Thanks for the suggestion. > See also https://lwn.net/Articles/505683/. Particularly (towards the end) > > If the device might be needed to power down other devices, such as an I2C > controller that might be needed to tell some regulator to turn off, then the > device should be activated for runtime PM purposes so that it will still be > active when runtime PM is disabled. > > (Rafael reviewed this article so it shouldn't be very far from the mark). > > >> >> The real mystery is why this happens on Beagle and Beagle-xM, but none >> of the other OMAP3 boards (at least the ones I have.) > > Maybe didn't components of the PMIC are active and have the potential to > generate an interrupt at an awkward time. USB and battery chargers seem good > at that. > > Or maybe due to the particular components active and the particular timing, > the pm_runtime_disable ends up freezing the runtime_pm state in 'on' rather > than 'off'. > >> >> Reproducing is easy. Simply run rtcwake in a loop: >> >> # while true; do rtcwake -m mem -s 1; done >> >> In my tests, this happens using omap2plus_defconfig (+ initramfs) on >> v3.6-rc1, v3.5, v3.4, v3.3 but seems to work fine on v3.2. >> >> I'm going on vacation for a few weeks, so any help debugging this would >> be greatly appreciated. > > Enjoy your vacation! I don't suppose it ends up in San Diego in late August > for one of the multitude of conferences there? No, I'll miss the summer conferences this year, this vacation will be unplugged. 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
