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 11:04:53 +0530
From:   Viresh Kumar <viresh.kumar@...aro.org>
To:     Pavel Machek <pavel@...x.de>
Cc:     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

On 21-07-20, 13:43, Pavel Machek wrote:
> On Mon 2020-07-20 17:37:50, Greg Kroah-Hartman wrote:
> > From: Finley Xiao <finley.xiao@...k-chips.com>
> > 
> > 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.
> > 
> > Fixes: 349d39dc5739 ("thermal: cpu_cooling: merge frequency and power tables")
> 
> Wow, this is completely different from the upstream patch.

Right, I have mentioned this in the patch I sent for stable.

https://lore.kernel.org/lkml/bc3978d0b7472c140e4d87f61138168a2a7b995c.1594194577.git.viresh.kumar@linaro.org/

> There the
> loops goes down, not up. The code does not match the changelog here.

Yes, the order is different in earlier kernels but I would say that
the changelog still matches as it doesn't necessarily talks about any
ordering here.

> > --- a/drivers/thermal/cpu_cooling.c
> > +++ b/drivers/thermal/cpu_cooling.c
> > @@ -278,11 +278,11 @@ static u32 cpu_power_to_freq(struct cpuf
> >  	int i;
> >  	struct freq_table *freq_table = cpufreq_cdev->freq_table;
> >  
> > -	for (i = 1; i <= cpufreq_cdev->max_level; i++)
> > -		if (power > freq_table[i].power)
> > +	for (i = 0; i < cpufreq_cdev->max_level; i++)
> > +		if (power >= freq_table[i].power)
> >  			break;
> >  
> > -	return freq_table[i - 1].frequency;
> > +	return freq_table[i].frequency;
> >  }
> 
> 
> 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 ?
-- 
viresh