From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Rafael J. Wysocki" Subject: Re: [PATCH] ARM: tegra: cpuidle: implement cpuidle_state.enter_freeze() Date: Thu, 09 Apr 2015 23:19:59 +0200 Message-ID: <285738930.THBQOWvsah@vostro.rjw.lan> References: <1428490480-10144-1-git-send-email-tomeu.vizoso@collabora.com> <20150408115546.GA24271@red-moon> <552643E1.3060200@collabora.com> Mime-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7Bit Return-path: In-Reply-To: <552643E1.3060200-ZGY8ohtN/8qB+jHODAdFcQ@public.gmane.org> Sender: linux-tegra-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Tomeu Vizoso Cc: Lorenzo Pieralisi , "linux-tegra-u79uwXL29TY76Z2rM5mHXA@public.gmane.org" , "linux-pm-u79uwXL29TY76Z2rM5mHXA@public.gmane.org" , "Rafael J. Wysocki" , Russell King , Stephen Warren , Thierry Reding , Alexandre Courbot , Bartlomiej Zolnierkiewicz , Kyungmin Park , Daniel Lezcano , Kukjin Kim , "linux-arm-kernel-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org" , "linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org" List-Id: linux-tegra@vger.kernel.org On Thursday, April 09, 2015 11:18:25 AM Tomeu Vizoso wrote: > On 04/08/2015 01:55 PM, Lorenzo Pieralisi wrote: > > On Wed, Apr 08, 2015 at 11:54:38AM +0100, Tomeu Vizoso wrote: > >> This callback is expected to do the same as enter() only that all > >> non-wakeup IRQs are expected to be disabled. > > > > This is not true or at least it is misworded. The enter_freeze() function > > is expected to return from the state with IRQs disabled at CPU level, or > > put it differently it must not re-enable IRQs while executing since the > > tick is frozen. > > True, only that it mentions interrupts in general, not just IRQs (I > don't know if the terminology used in the base code matches the one in > ARM's documentation). > > /* > * 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. > */ This means interrupts on the local CPU (ie. the thing done by local_irq_disable()). > >> 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. > >> > >> Signed-off-by: Tomeu Vizoso > >> Cc: Rafael J. Wysocki > >> --- > >> arch/arm/mach-tegra/cpuidle-tegra114.c | 31 ++++++++++++++++++++++++------- > >> 1 file changed, 24 insertions(+), 7 deletions(-) > >> > >> diff --git a/arch/arm/mach-tegra/cpuidle-tegra114.c b/arch/arm/mach-tegra/cpuidle-tegra114.c > >> index f2b586d..ef06001 100644 > >> --- a/arch/arm/mach-tegra/cpuidle-tegra114.c > >> +++ b/arch/arm/mach-tegra/cpuidle-tegra114.c > >> @@ -39,28 +39,44 @@ static int tegra114_idle_power_down(struct cpuidle_device *dev, > >> struct cpuidle_driver *drv, > >> int index) > >> { > >> - local_fiq_disable(); > >> - > >> tegra_set_cpu_in_lp2(); > >> cpu_pm_enter(); > >> > >> - clockevents_notify(CLOCK_EVT_NOTIFY_BROADCAST_ENTER, &dev->cpu); > >> - > >> call_firmware_op(prepare_idle); > >> > >> /* Do suspend by ourselves if the firmware does not implement it */ > >> if (call_firmware_op(do_idle, 0) == -ENOSYS) > >> cpu_suspend(0, tegra30_sleep_cpu_secondary_finish); > >> > >> - clockevents_notify(CLOCK_EVT_NOTIFY_BROADCAST_EXIT, &dev->cpu); > >> - > >> cpu_pm_exit(); > >> tegra_clear_cpu_in_lp2(); > >> > >> + return index; > >> +} > >> + > >> +static int tegra114_idle_enter(struct cpuidle_device *dev, > >> + struct cpuidle_driver *drv, > >> + int index) > >> +{ > >> + local_fiq_disable(); > >> + > >> + clockevents_notify(CLOCK_EVT_NOTIFY_BROADCAST_ENTER, &dev->cpu); > >> + > >> + index = tegra114_idle_power_down(dev, drv, index); > >> + > >> + clockevents_notify(CLOCK_EVT_NOTIFY_BROADCAST_EXIT, &dev->cpu); > >> + > >> local_fiq_enable(); > >> > >> return index; > >> } > >> + > >> +static void tegra114_idle_enter_freeze(struct cpuidle_device *dev, > >> + struct cpuidle_driver *drv, > >> + int index) > >> +{ > >> + tegra114_idle_power_down(dev, drv, index); > > > > Cool. So if the problem is FIQs, you don't disabled them on entry > > which means you enter the "frozen" state with FIQs enabled and tick frozen, > > unless I am missing something. > > I have gone a bit deeper in the code and that's correct, AFAICS. > > > The question here is: are we allowed to enable FIQs before returning > > from an enter_freeze() call (and to enter it with FIQs enabled) ? > > > > If we are not your code here certainly does not solve the issue, since > > it does _not_ disable FIQs upon enter_freeze call anyway. > > I think doing that would go against the wording of the comment I quoted > above, so I see two ways of fixing this: > > * Change the wording to refer to normal IRQs and leave the task of > enabling and disabling FIQs to the enter_freeze implementation (ugly and > I don't see any good reason for this) > > * Have FIQs already disabled when enter_freeze gets called, probably by > having arch_cpu_idle_enter do it on ARM (and the inverse in > arch_cpu_idle_exit)? > > Rafael, what's your opinion on this? I don't know what FIQs are. :-) ->enter_freeze is entered with interrupts disabled on the local CPU. It is not supposed to re-enable them. That is, while in the ->enter_freeze callback routine, the CPU must not be interrupted aby anything other than NMI. -- I speak only for myself. Rafael J. Wysocki, Intel Open Source Technology Center.