linux-kernel - Re: [PATCH] cpufreq/cppc: fix perf_to

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Date: Mon, 6 May 2024 10:55:09 +0800
From: "liwei (JK)" <liwei728@...wei.com>
To: Pierre Gondois <pierre.gondois@....com>
CC: <linux-acpi@...r.kernel.org>, <rafael@...nel.org>,
	<linux-kernel@...r.kernel.org>, <lenb@...nel.org>, <liwei391@...wei.com>,
	<viresh.kumar@...aro.org>
Subject: Re: [PATCH] cpufreq/cppc: fix perf_to_khz conversion exception

Hello Pierre,

Thanks for your reminder.

在 2024/5/3 15:42, Pierre Gondois 写道:
> Hello Liwei,
> 
> Thanks for the fix. I think there might be a similar issue
> in cppc_khz_to_perf(),
> 
> Regards,
> Pierre
> 

cppc_khz_to_perf() also has similar issue, I will modify the patch again.

Liwei

> On 4/30/24 12:12, liwei wrote:
>> When the nominal_freq recorded by the kernel is equal to lowest_freq and
>> the frequency reduction operation is triggered externally, there is a
>> conversion logic error in cppc_perf_to_khz(), causing the kernel to be
>> unable to feedback the true frequency.
>>
>> Fix this by adding the branch processing logic when nominal_freq is equal
>> to lowest_freq.
>>
>> Fixes: ec1c7ad47664 ("cpufreq: CPPC: Fix performance/frequency 
>> conversion")
>> Signed-off-by: liwei <liwei728@...wei.com>
>> ---
>>   drivers/acpi/cppc_acpi.c | 10 ++++++++--
>>   1 file changed, 8 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/acpi/cppc_acpi.c b/drivers/acpi/cppc_acpi.c
>> index a40b6f3946ef..92aac6974e0e 100644
>> --- a/drivers/acpi/cppc_acpi.c
>> +++ b/drivers/acpi/cppc_acpi.c
>> @@ -1869,9 +1869,15 @@ unsigned int cppc_perf_to_khz(struct 
>> cppc_perf_caps *caps, unsigned int perf)
>>       u64 mul, div;
>>       if (caps->lowest_freq && caps->nominal_freq) {
>> -        mul = caps->nominal_freq - caps->lowest_freq;
>> +        /* Avoid the special case when nominal_freq is equal to 
>> lowest_freq */
>> +        if (caps->lowest_freq == caps->nominal_freq) {
>> +            mul = caps->nominal_freq;
>> +            div = caps->nominal_perf;
>> +        } else {
>> +            mul = caps->nominal_freq - caps->lowest_freq;
>> +            div = caps->nominal_perf - caps->lowest_perf;
>> +        }
>>           mul *= KHZ_PER_MHZ;
>> -        div = caps->nominal_perf - caps->lowest_perf;
>>           offset = caps->nominal_freq * KHZ_PER_MHZ -
>>                div64_u64(caps->nominal_perf * mul, div);
>>       } else {