[PATCH] cpufreq/cppc: fix perf_to_khz conversion exception

[PATCH] cpufreq/cppc: fix perf_to_khz conversion exception

[liwei]

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@huawei.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 {
-- 
2.25.1

Re: [PATCH] cpufreq/cppc: fix perf_to_khz conversion exception

[Pierre Gondois]

Hello Liwei,

Thanks for the fix. I think there might be a similar issue
in cppc_khz_to_perf(),

Regards,
Pierre

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@huawei.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 {

Re: [PATCH] cpufreq/cppc: fix perf_to_khz conversion exception

[liwei (JK)]

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@huawei.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 {