linux-kernel - Re: [PATCH] cpufreq: Use a smaller freq for the policy->max when verify

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Date: Wed, 27 Mar 2024 16:21:00 +0100
From: "Rafael J. Wysocki" <rafael@...nel.org>
To: Viresh Kumar <viresh.kumar@...aro.org>, Xuewen Yan <xuewen.yan@...soc.com>
Cc: ke.wang@...soc.com, linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org, 
	xuewen.yan94@...il.com, di.shen@...soc.com
Subject: Re: [PATCH] cpufreq: Use a smaller freq for the policy->max when verify

On Wed, Mar 20, 2024 at 4:21 AM Viresh Kumar <viresh.kumar@...aro.org> wrote:
>
> On 19-03-24, 16:01, Xuewen Yan wrote:
> > When driver use the cpufreq_frequency_table_verify() as the
> > cpufreq_driver->verify's callback. It may cause the policy->max
> > bigger than the freq_qos's max freq.
> >
> > Just as follow:
> >
> > unisoc:/sys/devices/system/cpu/cpufreq/policy0 # cat scaling_available_frequencies
> > 614400 768000 988000 1228800 1469000 1586000 1690000 1833000 2002000 2093000
> >
> > unisoc:/sys/devices/system/cpu/cpufreq/policy0 # echo 1900000 > scaling_max_freq
> > unisoc:/sys/devices/system/cpu/cpufreq/policy0 # echo 1900000 > scaling_min_freq
> > unisoc:/sys/devices/system/cpu/cpufreq/policy0 # cat scaling_max_freq
> > 2002000
> > unisoc:/sys/devices/system/cpu/cpufreq/policy0 # cat scaling_min_freq
> > 2002000
> >
> > When user set the qos_min and qos_max as the same value, and the value
> > is not in the freq-table, the above scenario will occur.
> >
> > This is because in cpufreq_frequency_table_verify() func, when it can not
> > find the freq in table, it will change the policy->max to be a bigger freq,
> > as above, because there is no 1.9G in the freq-table, the policy->max would
> > be set to 2.002G. As a result, the cpufreq_policy->max is bigger than the
> > user's qos_max. This is unreasonable.
> >
> > So use a smaller freq when can not find the freq in fre-table, to prevent
>
>                                                       freq-table
>
> > the policy->max exceed the qos's max freq.
> >
> > Signed-off-by: Xuewen Yan <xuewen.yan@...soc.com>
> > ---
> >  drivers/cpufreq/freq_table.c | 8 ++++----
> >  1 file changed, 4 insertions(+), 4 deletions(-)
>
> Acked-by: Viresh Kumar <viresh.kumar@...aro.org>

Applied as 6.10 material, thanks!