On Wed, Sep 23, 2015 at 6:03 AM, Oliver Neukum <oneukum@xxxxxxx> wrote: > > On Tue, 2015-09-22 at 11:22 -0400, Alan Stern wrote: > > On Tue, 22 Sep 2015, Oliver Neukum wrote: > > > > > Cancel, yes, going to low power is a consequence which needn't bother > > > the power subsystem. > > > > Going to low power needn't involve the power subsystem? That sounds > > weird. > > Think of it like rfkill. It makes sense to suspend an rfkilled device. > It still is the job of the driver to report that its device is idle. > > > > You need a callback. If there are spurious > > > events, the current heuristics will keep devices awake. > > > You must discard them anyway, as they are spurious. There's no point > > > in transporting over the bus at all. We can cease IO for input. > > > > > > > This would create a parallel runtime-PM mechanism which is independent > > > > of the existing one. Is that really a good idea? > > > > > > It isn't strictly PM. It helps PM to do a better job, but > > > conceptually it is independent. > > > > So my next question is: _How_ can this help PM to do a better job? > > That is, what are the mechanisms? > > "inhibit" -> driver stops input -> driver sets PM count to zero > -> PM subsystem acts > > To go from the first to the second step a callback is needed > The IIO drivers use this model. The application keeps the fd open but there is a buffer enable switch to enable / disable input. Based on that trigger drivers use pm runtime put operations to induce PM idleness (and pm runtime get to wakeup the device). > > One you have already stated: Lack of spurious events will help prevent > > unwanted wakeups (or unwanted failures to go to sleep). > > That too. We also save CPU cycles. > > > But Dmitry made a stronger claim: Inhibiting an input device should > > allow the device to go to low power. I would like to know how we can > > implement this cleanly. The most straightforward approach is to use > > runtime PM, but it's not obvious how this can be made to work with the > > current API. > > Yes, we can use the current API. > The key is that you think of the mechanism as induced idleness, > not forced suspend. We already have a perfectly working mechanism > for suspending idle devices. > -- To unsubscribe from this list: send the line "unsubscribe linux-input" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
