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Date: Wed, 23 Sep 2015 10:27:56 +0300 From: Octavian Purdila <octavian.purdila@...el.com> To: Oliver Neukum <oneukum@...e.de> Cc: Alan Stern <stern@...land.harvard.edu>, Dmitry Torokhov <dmitry.torokhov@...il.com>, Irina Tirdea <irina.tirdea@...el.com>, Len Brown <len.brown@...el.com>, "Rafael J. Wysocki" <rafael@...nel.org>, Ulf Hansson <ulf.hansson@...aro.org>, "Rafael J. Wysocki" <rjw@...ysocki.net>, Pavel Machek <pavel@....cz>, "linux-input@...r.kernel.org" <linux-input@...r.kernel.org>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, "linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org> Subject: Re: [RFC PATCH] PM / Runtime: runtime: Add sysfs option for forcing runtime suspend On Wed, Sep 23, 2015 at 6:03 AM, Oliver Neukum <oneukum@...e.de> 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-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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