From mboxrd@z Thu Jan 1 00:00:00 1970 From: Mike Turquette Subject: Re: Arndale power management Date: Wed, 24 Jul 2013 18:58:42 -0700 Message-ID: <20130725015842.7598.97143@quantum> References: <611CFE9D6FBBDC4B97935A5287A11345014441@XSERVER21B.campus.tue.nl> Mime-Version: 1.0 Content-Transfer-Encoding: QUOTED-PRINTABLE Return-path: In-Reply-To: Sender: cpufreq-owner@vger.kernel.org List-ID: Content-Type: text/plain; charset="utf-8" To: Viresh Kumar , "Comaschi, F." Cc: Lukasz Majewski , Lists linaro-kernel , cpufreq@vger.kernel.org, Chander Kashyap , Linux PM List Quoting Viresh Kumar (2013-07-15 23:43:03) > Adding few more lists so that others can also help.. >=20 > On 15 July 2013 20:00, Comaschi, F. wrote: > > Dear Viresh, > > > > I am Francesco Comaschi, a researcher at Eindhoven University of Te= chnology. My research group is interested in implementing custom power = management policies on ARM-based platform (at the moment we are using a= n Arndale 5250 board featuring Exynos5 dual). We would like to make us= e of DVFS and to be able to measure power consumption on the board. >=20 > Ok. >=20 > > First of all, congratulations for the work that you and the other g= uys form the power management team are doing within the Linaro communit= y, I always follow your progress, and so far you have been the only rel= iable source of information for everything I have been doing on the boa= rd. >=20 > Thanks :) >=20 > > If you do not mind, I would like to ask you a few questions: > > 1) Is there a way to measure the board power consumption via softwa= re? I have read here: http://blogs.arm.com/software-enablement/925-linu= x-hwmon-power-management-and-arm-ds-5-streamline/ that it is possible w= ith the ARM Versatile boards, through the hwmon framework and lm_sensor= s. However, when I run lm_sensors on the Arndale board, no sensors were= found. Do you know about any other possible ways to measure power in s= oftware? Maybe it is possible to communicate with the on-board PMIC? Ma= ybe there are some registers where information about the power/voltage = provided to the processor and the other components is available? >=20 > On ARM Versatile express boards and the coretiles that come with it, > we have sensors which are probed through hwmon framework in > Linux. So, we have hardware IPs present on board which let us > get some power figures per cluster for big LITTLE. >=20 > I am not sure if Exynos have any such things on it. >=20 > @Chander: Are you aware of any such features? >=20 > > 2) Recently I have read Andy Green=E2=80=99s presentation =E2=80=9C= How to measure SoC power=E2=80=9D. However, by measuring power on the P= MIC input side through the ARM Energy Probe, probably I won't be able t= o see the effect of DVFS. Do you have any suggestions on how to measure= the effect of DVFS, even through hardware measurements? >=20 > You need probes on the voltage regulator which is feed the cores... > But again, that is very much hardware specific. And I haven't worked > on Exynos at all :) >=20 > > 3) More in general, I do not know which is the best way to implemen= t custom policies of DVFS. >=20 > I didn't get you here. Are you talking about tuning of governors here= ? >=20 > > Is it possible, maybe through appropriate API's, to access the cpu_= idle and the cpu_freq framework from inside my application? Shall I wor= k directly with the drivers of the PMIC? Is it possible to set the volt= age directly from inside my application? Are you trying to create a DVFS policy from a userspace application? Lots of people hack together something using the CPUfreq "userspace" governor and writing to: /sys/devices/system/cpu/cpu0/cpufreq/scaling_governor This is not something that should be shipped on a product but is useful for learning and prototyping. It only affects the CPU and will not help you craft DVFS policies on other peripherals/devices. Regards, Mike >=20 > Something on the board must provide this to kernel. Kernel can't > get it by itself. >=20 > _______________________________________________ > linaro-kernel mailing list > linaro-kernel@lists.linaro.org > http://lists.linaro.org/mailman/listinfo/linaro-kernel