linux-kernel - Re: [PATCH] cpufreq: Limit resolving a frequency to policy min/max

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Date: Thu, 22 Feb 2024 20:22:51 +0100
From: "Rafael J. Wysocki" <rafael@...nel.org>
To: Shivnandan Kumar <quic_kshivnan@...cinc.com>
Cc: "Rafael J . Wysocki" <rafael@...nel.org>, Viresh Kumar <viresh.kumar@...aro.org>, linux-pm@...r.kernel.org, 
	linux-kernel@...r.kernel.org, kernel@...cinc.com, quic_pkondeti@...cinc.com, 
	quic_namajain@...cinc.com, stable@...r.kernel.org
Subject: Re: [PATCH] cpufreq: Limit resolving a frequency to policy min/max

On Thu, Feb 22, 2024 at 9:35 AM Shivnandan Kumar
<quic_kshivnan@...cinc.com> wrote:
>
> Resolving a frequency to an efficient one should not transgress policy->max
> (which can be set for thermal reason) and policy->min. Currently there is
> possibility where scaling_cur_freq can exceed scaling_max_freq when
> scaling_max_freq is inefficient frequency. Add additional check to ensure
> that resolving a frequency will respect policy->min/max.
>
> Fixes: 1f39fa0dccff ("cpufreq: Introducing CPUFREQ_RELATION_E")
> Signed-off-by: Shivnandan Kumar <quic_kshivnan@...cinc.com>
> ---
>  include/linux/cpufreq.h | 18 +++++++++++++++++-
>  1 file changed, 17 insertions(+), 1 deletion(-)
>
> diff --git a/include/linux/cpufreq.h b/include/linux/cpufreq.h
> index afda5f24d3dd..42d98b576a36 100644
> --- a/include/linux/cpufreq.h
> +++ b/include/linux/cpufreq.h
> @@ -1021,6 +1021,19 @@ static inline int cpufreq_table_find_index_c(struct cpufreq_policy *policy,
>                                                    efficiencies);
>  }
>
> +static inline bool cpufreq_table_index_is_in_limits(struct cpufreq_policy *policy,
> +                                                   int idx)

This is not really about the index only, but about the frequency at
that index too, so I'd call the function differently.

> +{
> +       unsigned int freq;
> +
> +       if (idx < 0)
> +               return false;
> +
> +       freq = policy->freq_table[idx].frequency;
> +
> +       return (freq == clamp_val(freq, policy->min, policy->max));

Redundant outer parens.

> +}
> +
>  static inline int cpufreq_frequency_table_target(struct cpufreq_policy *policy,
>                                                  unsigned int target_freq,
>                                                  unsigned int relation)
> @@ -1054,7 +1067,10 @@ static inline int cpufreq_frequency_table_target(struct cpufreq_policy *policy,
>                 return 0;
>         }
>
> -       if (idx < 0 && efficiencies) {
> +       /*
> +        * Limit frequency index to honor policy->min/max
> +        */

This comment need not be multi-line.

> +       if (!cpufreq_table_index_is_in_limits(policy, idx) && efficiencies) {
>                 efficiencies = false;
>                 goto retry;
>         }
> --

Thanks!