linux-kernel - Re: [PATCH 4.19 123/133] thermal/drivers/cpufreq_cooling: Fix wrong frequency converted from power

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Date:   Wed, 22 Jul 2020 09:43:17 +0200
From:   Pavel Machek <pavel@...x.de>
To:     Viresh Kumar <viresh.kumar@...aro.org>
Cc:     Pavel Machek <pavel@...x.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        Finley Xiao <finley.xiao@...k-chips.com>,
        Amit Kucheria <amit.kucheria@...aro.org>,
        Daniel Lezcano <daniel.lezcano@...aro.org>
Subject: Re: [PATCH 4.19 123/133] thermal/drivers/cpufreq_cooling: Fix wrong
 frequency converted from power

Hi!

> > > commit 371a3bc79c11b707d7a1b7a2c938dc3cc042fffb upstream.
> > > 
> > > The function cpu_power_to_freq is used to find a frequency and set the
> > > cooling device to consume at most the power to be converted. For example,
> > > if the power to be converted is 80mW, and the em table is as follow.
> > > struct em_cap_state table[] = {
> > > 	/* KHz     mW */
> > > 	{ 1008000, 36, 0 },
> > > 	{ 1200000, 49, 0 },
> > > 	{ 1296000, 59, 0 },
> > > 	{ 1416000, 72, 0 },
> > > 	{ 1512000, 86, 0 },
> > > };
> > > The target frequency should be 1416000KHz, not 1512000KHz.
> > >
...
> > Something is very wrong here, if table is sorted like described in the
> > changelog, it will always break at i==0 or i==1... not working at all
> > in the old or the new version.
> 
> As I understand from the other email you sent, this works fine now.
> Right ?

Yes, I believe the code is okay now.

OTOH the changelog is extremely confusing, because code would not work
on the table presented there as an example.

Best regards,
								Pavel
-- 
DENX Software Engineering GmbH,      Managing Director: Wolfgang Denk
HRB 165235 Munich, Office: Kirchenstr.5, D-82194 Groebenzell, Germany

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