On Thu, 22 Sep 2016, Ulf Hansson wrote: > >> > > An observation I made, is when the sdmmc device gets runtime resumed > >> > > (pm_runtime_get_sync()), the parent device (the usb device) may also > >> > > become runtime resumed (unless it's already). In this sequence, but > >> > > *only* when actually runtime resuming the usb device, the runtime PM > >> > > core decides to update the last busy mark for the usb device. Should > >> > > it really do that? > >> > > >> > Yes, that's deliberate. The whole idea of autosuspend is to prevent > >> > the device from being runtime-suspended too soon after it was used, and > >> > the PM core considers runtime-resume to be a form of usage. > >> > >> I understand it's deliberate, but I was more question whether we > >> actually should have the runtime PM core to behaves like this. > >> > >> I don't think its behaviour is consistent, as in such case all calls > >> to __pm_runtime_resume() should trigger the runtime PM core to update > >> the last busy mark. > > > > Not a bad idea... > > Yes, it is. :-) > > Although, I am still concerned about he inconsistent behaviour. > > > > >> Don't get me wrong, I am *not* suggesting we should do that change, as > >> it would mean the last busy mark would be updated way too often. > > > > The updates aren't very expensive. Just one atomic write. It probably > > takes less time than acquiring the runtime-PM spinlock. > > > >> Instead, perhaps it's better to leave the responsibility of updating > >> the last busy mark to the runtime PM users solely. > > > > Maybe, but I think doing it once in the core, like this, can remove the > > need for a lot of function calls in drivers. > > Unfortunate not. Most updates of the last busy mark happens when a > device is no longer required to be runtime resumed. As when a driver > has completed to serve a request and is about to call pm_runtime_put() > (or similar API). > > So, I still believe doing it in the runtime PM core is just a waste. > > I think it's better to leave the update to the users entirely, it > would become consistent but also more flexible, as one could easily > think of situations where you may in some cases want to update the > last busy mark and in some other not. You can try making this change if you want. I'd be afraid of regressions. Alan Stern -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
