Re: [RFC PATCH v5 6/6] cpufreq/freq_table: Allow decreasing cpuinfo.max_freq

[Pierre Gondois <pierre.gondois@arm.com>]

On 3/11/26 17:24, Rafael J. Wysocki wrote:
> On Wed, Feb 25, 2026 at 9:50 AM Pierre Gondois<pierre.gondois@arm.com> wrote:
>> Drivers not using freq. tables update cpuinfo.max_freq in their
>> .set_boost() callback. E.g. amd-pstate, cppc_cpufreq.
>> Drivers relying on freq. tables and supporting boost frequencies
>> rely on cpufreq_frequency_table_cpuinfo(). cpuinfo.max_freq is
>> only updated if the new maximal value is higher than the previous
>> one.
>>
>> Using the scmi-cpufreq driver which relies on freq. tables, enabling
>> boost will permanently increases the cpuinfo.max_freq value.
>> This patch allows to lower cpuinfo.max_freq.
>>
>> Note:
>> commit 538b0188da46 ("cpufreq: ACPI: Set cpuinfo.max_freq directly
>> if max boost is known")
>> favored having cpuinfo.max_freq reporting the maximal boosted
>> frequency of a CPU instead of the maximal reachable frequency
>> due to regressions in the frequency reported by cpuinfo.max
>> and scaling_cur_freq.
>> As stated above, this is not what most of the other cpufreq driver
>> do. I assume that the following patch:
>> commit 3c55e94c0ade ("cpufreq: ACPI: Extend frequency tables to
>> cover boost frequencies")
>> was correct, but might not have tagged the boosted frequency with
>> the CPUFREQ_BOOST_FREQ flag in the freq. table.
>>
>> Signed-off-by: Pierre Gondois<pierre.gondois@arm.com>
>> ---
>>   drivers/cpufreq/freq_table.c | 7 +------
>>   1 file changed, 1 insertion(+), 6 deletions(-)
>>
>> diff --git a/drivers/cpufreq/freq_table.c b/drivers/cpufreq/freq_table.c
>> index 9b37f37c36389..bd08cbe9e9ba3 100644
>> --- a/drivers/cpufreq/freq_table.c
>> +++ b/drivers/cpufreq/freq_table.c
>> @@ -50,12 +50,7 @@ int cpufreq_frequency_table_cpuinfo(struct cpufreq_policy *policy)
>>          }
>>
>>          policy->cpuinfo.min_freq = min_freq;
>> -       /*
>> -        * If the driver has set its own cpuinfo.max_freq above max_freq, leave
>> -        * it as is.
>> -        */
>> -       if (policy->cpuinfo.max_freq < max_freq)
>> -               policy->cpuinfo.max_freq = max_freq;
>> +       policy->cpuinfo.max_freq = max_freq;
>>
>>          if (min_freq == ~0)
>>                  return -EINVAL;
>> --
> How exactly does this change depend on the previous patches?

Without it, the pattern in the cover letter:

# ## Init
scaling_max_freq:1000000
cpuinfo_max_freq:1000000

# echo 700000 > scaling_max_freq
scaling_max_freq:700000
cpuinfo_max_freq:1000000

# echo 1 > ../boost
scaling_max_freq:700000
cpuinfo_max_freq:1200000

# echo 800000 > scaling_max_freq
scaling_max_freq:800000
cpuinfo_max_freq:1200000

# echo 0 > ../boost
scaling_max_freq:800000
cpuinfo_max_freq:1000000

doesn't work when using the scmi-cpufreq driver