[PATCH v3 1/2] cppc_cpufreq: Use desired perf if feedback ctrs are 0 or unchanged

[Jie Zhan]

On 25/09/2024 17:28, lihuisong (C) wrote:
> Hi Jie,
> 
> LGTM except for some trivial,
> Reviewed-by: Huisong Li <lihuisong at huawei.com>

Thanks.

> 
> 
> 在 2024/9/19 16:45, Jie Zhan 写道:
>> The CPPC performance feedback counters could be 0 or unchanged when the
>> target cpu is in a low-power idle state, e.g. power-gated or clock-gated.
>>
>> When the counters are 0, cppc_cpufreq_get_rate() returns 0 KHz, which makes
>> cpufreq_online() get a false error and fail to generate a cpufreq policy.
>>
>> When the counters are unchanged, the existing cppc_perf_from_fbctrs()
>> returns a cached desired perf, but some platforms may update the real
>> frequency back to the desired perf reg.
>>
>> For the above cases in cppc_cpufreq_get_rate(), get the latest desired perf
>> to reflect the frequency; if failed, return the cached desired perf.
>>
>> Fixes: 6a4fec4f6d30 ("cpufreq: cppc: cppc_cpufreq_get_rate() returns zero in all error cases.")
>> Signed-off-by: Jie Zhan <zhanjie9 at hisilicon.com>
>> Reviewed-by: Zeng Heng <zengheng4 at huawei.com>
>> Reviewed-by: Ionela Voinescu <ionela.voinescu at arm.com>
>> ---
>>   drivers/cpufreq/cppc_cpufreq.c | 49 +++++++++++++++++++++++++++-------
>>   1 file changed, 39 insertions(+), 10 deletions(-)
>>
>> diff --git a/drivers/cpufreq/cppc_cpufreq.c b/drivers/cpufreq/cppc_cpufreq.c
>> index bafa32dd375d..e55192303a9f 100644
>> --- a/drivers/cpufreq/cppc_cpufreq.c
>> +++ b/drivers/cpufreq/cppc_cpufreq.c
>> @@ -118,6 +118,9 @@ static void cppc_scale_freq_workfn(struct kthread_work *work)
>>         perf = cppc_perf_from_fbctrs(cpu_data, &cppc_fi->prev_perf_fb_ctrs,
>>                        &fb_ctrs);
>> +    if (!perf)
>> +        return;
>> +
>>       cppc_fi->prev_perf_fb_ctrs = fb_ctrs;
>>         perf <<= SCHED_CAPACITY_SHIFT;
>> @@ -726,11 +729,26 @@ static int cppc_perf_from_fbctrs(struct cppc_cpudata *cpu_data,
>>         /* Check to avoid divide-by zero and invalid delivered_perf */
> Now this comment can be removed, right?

Didn't notice this comment, but, having a check, I think it still fits.
'!delta_reference' avoids divide-by zero, and '!delta_delivered' checks
invalid delivered_perf.

So I think we just leave it unchanged.

>>       if (!delta_reference || !delta_delivered)
>> -        return cpu_data->perf_ctrls.desired_perf;
>> +        return 0;
>>         return (reference_perf * delta_delivered) / delta_reference;
>>   }
>>   +static int cppc_get_perf_ctrs_sample(int cpu,
>> +                     struct cppc_perf_fb_ctrs *fb_ctrs_t0,
>> +                     struct cppc_perf_fb_ctrs *fb_ctrs_t1)
>> +{
>> +    int ret;
>> +
>> +    ret = cppc_get_perf_ctrs(cpu, fb_ctrs_t0);
>> +    if (ret)
>> +        return ret;
>> +
>> +    udelay(2); /* 2usec delay between sampling */
>> +
>> +    return cppc_get_perf_ctrs(cpu, fb_ctrs_t1);
>> +}
>> +
>>   static unsigned int cppc_cpufreq_get_rate(unsigned int cpu)
>>   {
>>       struct cppc_perf_fb_ctrs fb_ctrs_t0 = {0}, fb_ctrs_t1 = {0};
>> @@ -746,18 +764,29 @@ static unsigned int cppc_cpufreq_get_rate(unsigned int cpu)
>>         cpufreq_cpu_put(policy);
>>   -    ret = cppc_get_perf_ctrs(cpu, &fb_ctrs_t0);
>> -    if (ret)
>> -        return 0;
>> -
>> -    udelay(2); /* 2usec delay between sampling */
>> -
>> -    ret = cppc_get_perf_ctrs(cpu, &fb_ctrs_t1);
>> -    if (ret)
>> -        return 0;
>> +    ret = cppc_get_perf_ctrs_sample(cpu, &fb_ctrs_t0, &fb_ctrs_t1);
>> +    if (ret) {
>> +        if (ret == -EFAULT)
>> +            goto out_invalid_counters;
> suggest that add some comments for ret == -EFAULT case.
> Because this error code depands on the implementation of cppc_get_perf_ctrs.
> If add a new exception case which also return -EFAULT, then this switch is unreasonable.

Sure. What about adding the following comment:

/* -EFAULT indicates that any of the associated CPPC regs is 0. */

Thanks,
Jie