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

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Date:   Tue, 21 Jul 2020 13:43:44 +0200
From:   Pavel Machek <pavel@...x.de>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        Finley Xiao <finley.xiao@...k-chips.com>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        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 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. There the
loops goes down, not up. The code does not match the changelog 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.

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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