From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
	id S1755863AbcCDCQF (ORCPT <rfc822;w@1wt.eu>);
	Thu, 3 Mar 2016 21:16:05 -0500
Received: from mail-lb0-f196.google.com ([209.85.217.196]:33259 "EHLO
	mail-lb0-f196.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
	with ESMTP id S1750794AbcCDCQC (ORCPT
	<rfc822;linux-kernel@vger.kernel.org>);
	Thu, 3 Mar 2016 21:16:02 -0500
MIME-Version: 1.0
In-Reply-To: <20160303060003.GJ2891@vireshk-i7>
References: <2495375.dFbdlAZmA6@vostro.rjw.lan>
	<26020775.9hJG2SHiH2@vostro.rjw.lan>
	<20160303060003.GJ2891@vireshk-i7>
Date: Fri, 4 Mar 2016 03:15:59 +0100
X-Google-Sender-Auth: 28lqEvd9_i7wpPwYaeWDx_vBghI
Message-ID: <CAJZ5v0inN24WujzEps+oe0gDcdAP8RjyB1Y2+DbBP044RKpOhA@mail.gmail.com>
Subject: Re: [PATCH 5/6] cpufreq: Support for fast frequency switching
From: "Rafael J. Wysocki" <rafael@kernel.org>
To: Viresh Kumar <viresh.kumar@linaro.org>
Cc: "Rafael J. Wysocki" <rjw@rjwysocki.net>,
        Linux PM list <linux-pm@vger.kernel.org>,
        Juri Lelli <juri.lelli@arm.com>,
        Steve Muckle <steve.muckle@linaro.org>,
        ACPI Devel Maling List <linux-acpi@vger.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Peter Zijlstra <peterz@infradead.org>,
        Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>,
        Vincent Guittot <vincent.guittot@linaro.org>,
        Michael Turquette <mturquette@baylibre.com>
Content-Type: text/plain; charset=UTF-8
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

On Thu, Mar 3, 2016 at 7:00 AM, Viresh Kumar <viresh.kumar@linaro.org> wrote:
> On 02-03-16, 03:12, Rafael J. Wysocki wrote:
>> Index: linux-pm/drivers/cpufreq/cpufreq.c
>> ===================================================================
>> --- linux-pm.orig/drivers/cpufreq/cpufreq.c
>> +++ linux-pm/drivers/cpufreq/cpufreq.c
>> @@ -1772,6 +1772,39 @@ EXPORT_SYMBOL(cpufreq_unregister_notifie
>>   *                              GOVERNORS                            *
>>   *********************************************************************/
>>
>> +/**
>> + * cpufreq_driver_fast_switch - Carry out a fast CPU frequency switch.
>> + * @policy: cpufreq policy to switch the frequency for.
>> + * @target_freq: New frequency to set (may be approximate).
>> + * @relation: Relation to use for frequency selection.
>> + *
>> + * Carry out a fast frequency switch from interrupt context.
>> + *
>> + * This function must not be called if policy->fast_switch_possible is unset.
>> + *
>> + * Governors calling this function must guarantee that it will never be invoked
>> + * twice in parallel for the same policy and that it will never be called in
>> + * parallel with either ->target() or ->target_index() for the same policy.
>> + *
>> + * If CPUFREQ_ENTRY_INVALID is returned by the driver's ->fast_switch()
>> + * callback, the hardware configuration must be preserved.
>> + */
>> +void cpufreq_driver_fast_switch(struct cpufreq_policy *policy,
>> +                             unsigned int target_freq, unsigned int relation)
>> +{
>> +     unsigned int freq;
>> +
>> +     if (target_freq == policy->cur)
>
> Maybe an unlikely() here ?
>
>> +             return;
>> +
>> +     freq = cpufreq_driver->fast_switch(policy, target_freq, relation);
>> +     if (freq != CPUFREQ_ENTRY_INVALID) {
>> +             policy->cur = freq;
>
> Hmm.. What will happen to the code relying on the cpufreq-notifiers
> now ?

It will have a problem.

For that code it's like the CPU changing the frequency and not telling
it (which is not unusual for that matter).

Thanks,
Rafael