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Date: Thu, 10 Nov 2016 12:18:43 -0600 From: Andy Gross <andy.gross@...aro.org> To: Sudeep Holla <sudeep.holla@....com> Cc: linux-pm@...r.kernel.org, "Rafael J . Wysocki" <rjw@...ysocki.net>, Linux Kernel list <linux-kernel@...r.kernel.org>, Daniel Lezcano <daniel.lezcano@...aro.org>, Lorenzo Pieralisi <lorenzo.pieralisi@....com>, Vincent Guittot <vincent.guittot@...aro.org> Subject: Re: [PATCH v2] drivers: cpuidle: assign enter_freeze to same as enter callback function On 10 November 2016 at 08:24, Sudeep Holla <sudeep.holla@....com> wrote: > enter_freeze() callback is expected atleast to do the same as enter() > but it has to guarantee that interrupts aren't enabled at any point > in its execution, as the tick is frozen. > > CPUs execute ->enter_freeze with the local tick or entire timekeeping > suspended, so it must not re-enable interrupts at any point (even > temporarily) or attempt to change states of clock event devices. > > It will be called when the system goes to suspend-to-idle and will > reduce power usage because CPUs won't be awaken for unnecessary IRQs > (i.e. woken up only on IRQs from "wakeup sources") > > We can reuse the same code for both the enter() and enter_freeze() > callbacks as along as they don't re-enable interrupts. Only "coupled" > cpuidle mechanism enables interrupts and doing that with timekeeping > suspended is generally not safe. > > Since this generic DT based idle driver doesn't support "coupled" > states, it is safe to assume that the interrupts are not re-enabled. > > This patch assign enter_freeze to same as enter callback function which > helps to save power without any intermittent spurious wakeups from > suspend-to-idle. > > Cc: "Rafael J. Wysocki" <rjw@...ysocki.net> > Signed-off-by: Sudeep Holla <sudeep.holla@....com> Tested this on a Qualcomm 410c dragonboard. Worked great. Thanks for the patch! Tested-by: Andy Gross <andy.gross@...aro.org>
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