linux-kernel - Re: [PATCH V3 8/9] cpufreq: Keep policy->freq

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Message-ID: <20160607042807.GC21466@vireshk-i7>
Date:	Tue, 7 Jun 2016 09:58:07 +0530
From:	Viresh Kumar <viresh.kumar@...aro.org>
To:	"Rafael J. Wysocki" <rafael@...nel.org>
Cc:	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Steve Muckle <steve.muckle@...aro.org>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Paul Mackerras <paulus@...ba.org>,
	Michael Ellerman <mpe@...erman.id.au>,
	Linaro Kernel Mailman List <linaro-kernel@...ts.linaro.org>,
	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	"linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>,
	Dmitry Eremin-Solenikov <dbaryshkov@...il.com>,
	Krzysztof Kozlowski <k.kozlowski@...sung.com>,
	Kukjin Kim <kgene@...nel.org>, Steven Miao <realmz6@...il.com>
Subject: Re: [PATCH V3 8/9] cpufreq: Keep policy->freq_table sorted in
 ascending order

On 06-06-16, 23:56, Rafael J. Wysocki wrote:
> Since you are adding new code, you can write it so it doesn't do
> unnecessary checks from the start.

Hmm, I will do all that in this series only now.

> While at it, the "if ((freq < policy->min) || (freq > policy->max))"
> checks in cpufreq_find_index_l() and cpufreq_find_index_h() don't look
> good to me, because they very well may cause those function to return
> -EINVAL even when there's a valid table and that may cause
> acpi_cpufreq_fast_switch() to do bad things.

Hmm. So, the checks are for sure required here, otherwise we may end up
returning a frequency which we aren't allowed to. Also note that 'freq' here
isn't the target-freq, but the entry in the freq-table.

This routine should be returning a valid freq within the ranges specified by
policy->min/max.

Also note that these routines shall *never* return -EINVAL, otherwise it is
mostly a bug we are hitting.

We have enough checks in place to make sure that there is at least one valid
entry in the freq-table which is >= policy->min and <= policy->max.

I will take care of rest of the comments though. Thanks.

-- 
viresh