From mboxrd@z Thu Jan 1 00:00:00 1970 From: Sudeep Holla Subject: Re: [PATCH v2 02/10] cpufreq: provide data for frequency-invariant load-tracking support Date: Thu, 13 Jul 2017 13:49:27 +0100 Message-ID: References: <20170706094948.8779-1-dietmar.eggemann@arm.com> <22f004af-0158-8265-2da5-34743f294bfb@arm.com> <12829054.TWIodSo4bb@aspire.rjw.lan> <20170711060106.GL2928@vireshk-i7> <45224055-7bf1-243b-9366-0f2d3442ef59@arm.com> <20170712040917.GG17115@vireshk-i7> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Return-path: Received: from foss.arm.com ([217.140.101.70]:38042 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751176AbdGMMtd (ORCPT ); Thu, 13 Jul 2017 08:49:33 -0400 In-Reply-To: <20170712040917.GG17115@vireshk-i7> Content-Language: en-US Sender: linux-pm-owner@vger.kernel.org List-Id: linux-pm@vger.kernel.org To: Viresh Kumar , Dietmar Eggemann Cc: Sudeep Holla , "Rafael J. Wysocki" , Peter Zijlstra , "Rafael J. Wysocki" , Linux Kernel Mailing List , Linux PM , Russell King - ARM Linux , Greg Kroah-Hartman , Russell King , Catalin Marinas , Will Deacon , Juri Lelli , Vincent Guittot , Morten Rasmussen On 12/07/17 05:09, Viresh Kumar wrote: > On 11-07-17, 16:06, Dietmar Eggemann wrote: >> But in the meantime we're convinced that cpufreq_driver_fast_switch() is >> not the right place to call arch_set_freq_scale() since for (future) >> arm/arm64 fast-switch driver, the return value of >> cpufreq_driver->fast_switch() does not give us the information that the >> frequency value did actually change. > > Yeah, I saw your discussion with Peter on #linux-rt IRC and TBH I wasn't aware > that we are going to do fast switching that way. Just trying to get > understanding of that idea a bit.. > > So we will do fast switching from scheduler's point of view, i.e. we wouldn't > schedule a kthread to change the frequency. But the real hardware still can't do > that without sleeping, like if we have I2C somewhere in between. AFAIU, we will > still have some kind of *software* bottom half to do that work, isn't it? And it > wouldn't be that we have pushed some instructions to the hardware, which it can > do a bit later. > No the platforms we are considering are only where a standard firmware interface is provided and the firmware deals with all those I2C/PMIC crap. > For example, the regulator may be accessed via I2C and we need to program that > before changing the clock. So, it will be done by some software code only. > Software but just not Linux OSPM but some firmware(remote processors presumably, can't imagine on the same processor though) -- Regards, Sudeep