From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-8.5 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id B855FC433DF for ; Mon, 3 Aug 2020 13:26:20 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id A018120775 for ; Mon, 3 Aug 2020 13:26:20 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727023AbgHCN0U (ORCPT ); Mon, 3 Aug 2020 09:26:20 -0400 Received: from foss.arm.com ([217.140.110.172]:57636 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727021AbgHCN0T (ORCPT ); Mon, 3 Aug 2020 09:26:19 -0400 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 1740230E; Mon, 3 Aug 2020 06:26:19 -0700 (PDT) Received: from localhost (unknown [10.1.198.53]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id AC5A63F71F; Mon, 3 Aug 2020 06:26:18 -0700 (PDT) Date: Mon, 3 Aug 2020 14:26:17 +0100 From: Ionela Voinescu To: Viresh Kumar Cc: "Rafael J. Wysocki" , "Rafael J. Wysocki" , Dietmar Eggemann , Catalin Marinas , Sudeep Holla , Will Deacon , Russell King - ARM Linux , Ingo Molnar , Peter Zijlstra , Linux PM , Linux ARM , Linux Kernel Mailing List , Valentin Schneider Subject: Re: [PATCH v2 1/7] cpufreq: move invariance setter calls in cpufreq core Message-ID: <20200803132617.GA9512@arm.com> References: <20200722093732.14297-1-ionela.voinescu@arm.com> <20200722093732.14297-2-ionela.voinescu@arm.com> <20200730034128.k4fmblfuwjcmqdze@vireshk-mac-ubuntu> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200730034128.k4fmblfuwjcmqdze@vireshk-mac-ubuntu> User-Agent: Mutt/1.9.4 (2018-02-28) Sender: linux-pm-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-pm@vger.kernel.org Hi guys, On Thursday 30 Jul 2020 at 09:11:28 (+0530), Viresh Kumar wrote: > On 27-07-20, 15:48, Rafael J. Wysocki wrote: > > On Wed, Jul 22, 2020 at 11:38 AM Ionela Voinescu > > wrote: > > > diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c > > > index 036f4cc42ede..bac4101546db 100644 > > > --- a/drivers/cpufreq/cpufreq.c > > > +++ b/drivers/cpufreq/cpufreq.c > > > @@ -2058,9 +2058,16 @@ EXPORT_SYMBOL(cpufreq_unregister_notifier); > > > unsigned int cpufreq_driver_fast_switch(struct cpufreq_policy *policy, > > > unsigned int target_freq) > > > { > > > + unsigned int freq; > > > + > > > target_freq = clamp_val(target_freq, policy->min, policy->max); > > > + freq = cpufreq_driver->fast_switch(policy, target_freq); > > > + > > > + if (freq) > > > + arch_set_freq_scale(policy->related_cpus, freq, > > > + policy->cpuinfo.max_freq); > > > > Why can't arch_set_freq_scale() handle freq == 0? > Sorry, I seem to have missed this question the first time around. arch_set_freq_scale() could handle freq == 0, but given that freq == 0 is signaling an error here, I do believe this check is well placed, to prevent a useless call to arch_set_freq_scale(). Also [1]: """ * If 0 is returned by the driver's ->fast_switch() callback to indicate an * error condition, the hardware configuration must be preserved. */ """ > Actually there is no need to. AFAIU the freq returned by fast_switch > can never be 0 (yeah qcom driver does it right now and I am fixing > it). And so we can drop this check altogether. > It's not only the qcom driver, it's also the scmi driver that could return 0 [2]. But I don't think "fixing" these drivers is the solution, given that 0 is indicated as a valid return value of .fast_switch() to signal an error condition [1], while schedutil (the caller), also does validation that the returned frequency is !0 before setting it as current frequency [3]. Therefore, it is know and (somewhat) documented that 0 indicates an error condition and it should be allowed as a return value for .fast_switch(). Also, I believe is a good idea to leave the option for drivers to return 0 (signaling error) from their implementation of .fast_switch(). [1] https://elixir.bootlin.com/linux/v5.8-rc4/source/drivers/cpufreq/cpufreq.c#L2043 [2] https://elixir.bootlin.com/linux/v5.8-rc4/source/drivers/cpufreq/scmi-cpufreq.c#L76 [3] https://elixir.bootlin.com/linux/v5.8-rc4/source/kernel/sched/cpufreq_schedutil.c#L124 Thanks, Ionela. > -- > viresh