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Date: Tue, 10 Dec 2013 09:25:16 +0100 From: Daniel Lezcano <daniel.lezcano@...aro.org> To: anish singh <anish198519851985@...il.com> CC: Alex Shi <alex.shi@...aro.org>, Frederic Weisbecker <fweisbec@...il.com>, LAK <linux-arm-kernel@...ts.infradead.org>, "tglx@...utronix.de" <tglx@...utronix.de>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, preeti@...ux.vnet.ibm.com, "len.brown@...el.com" <len.brown@...el.com> Subject: Re: questions of cpuidle On 12/10/2013 09:07 AM, anish singh wrote: > On Mon, Dec 9, 2013 at 11:27 PM, Daniel Lezcano > <daniel.lezcano@...aro.org> wrote: >> On 12/10/2013 07:33 AM, Alex Shi wrote: >>> >>> On 12/09/2013 10:17 PM, Daniel Lezcano wrote: >>>> >>>> >>>> Concerning the wake up of the cpu: the cpu disabled the irq and >>>> goes to sleep, it is up to the firmware to wake up the cpu when an >>>> interrupt occurs. It will exits its sleep state, call >>>> clock_events_notify(EXIT), by this way re-switching to the local >>>> timer, and then re-enabling the local interrupt which leads to the >>>> interrupt handler. >>> >>> >>> Thanks a lots for excellent article and detailed explains! >>> >>> So, if the firmware is in response to wake up cpu. that means there >>> is a unit which control the firmware and it can not be power down. >> >> >> Correct. >> >> >>> Do you know which unit running the firmware to wake up deep idle >>> CPU. >> >> >> That depends on the SoC implementation. > and which is intentionally kept hidden away. >> >> Some SoC have a "Power Management Unit". The PMU has several idle states >> defined, each of them are described in the technical reference manual >> (TRM) with the wake up sources. > PMU is intentionally kept hidden by OEM companies as this way > they protect there hardware IP. Unfortunately yes and beside that hiding the bugs in a black box letting the user/developer to bang its head against the walls :) >> Some SoC don't have any PMU and the idle states are very few, keeping >> most of the logic on. >> >> Some other SoC hide the PMU behind PSCI calls. > which is intentional. >>> And does the wake up pass via GIC to CPU? If so, does the GIC need >>> keep awake when all cpu idle? If not, how the firmware give the >>> interrupt to CPU? And I am wondering if the deep idle cpu voltage get >>> to near 0. How the cpu get the interrupt signal? >> >> >> If a deep idle state powers down the GIC, it is up to the PMU to proxy >> the interrupts. When an interrupt occurs, the PMU powers up the logic, >> including the GIC. The notifier call chain with cpu_suspend / cpu_resume >> will save and restore the GIC registers. >> >> But this is hardware specific and will depend on how the PMU is >> implemented and how far it goes in the power management. >> >> You have a good example in the drivers/cpuidle/cpuidle-ux500.c to >> understand with the comments how the interrupts are handled through the >> power management unit. >> >> In the Xillinx documentation available on the web [1], the chapter 24.4 >> gives the information about one kind of PMU. >> >> I believe the mechanism is pretty similar on all the hardware but it is >> obfuscated by a generic power instruction like mwait. >> >> -- Daniel >> >> [1] >> http://www.xilinx.com/support/documentation/user_guides/ug585-Zynq-7000-TRM.pdf >> >> >> >>>> There are some more informations in the wiki page [1]. >>>> >>>> -- Daniel >>>> >>>> [1] >>>> https://wiki.linaro.org/WorkingGroups/PowerManagement/Doc/WakeUpSources >>> >>> >>>> >>> >> >> >> -- >> <http://www.linaro.org/> Linaro.org │ Open source software for ARM SoCs >> >> Follow Linaro: <http://www.facebook.com/pages/Linaro> Facebook | >> <http://twitter.com/#!/linaroorg> Twitter | >> <http://www.linaro.org/linaro-blog/> Blog >> >> -- >> 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/ -- <http://www.linaro.org/> Linaro.org │ Open source software for ARM SoCs Follow Linaro: <http://www.facebook.com/pages/Linaro> Facebook | <http://twitter.com/#!/linaroorg> Twitter | <http://www.linaro.org/linaro-blog/> Blog -- 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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