Re: [PATCH] cpufreq: CPPC: Return desired perf in ->get() if feedback counters are 0

Jie Zhan
2024-08-28T02:19:31Z

Can anyone take a look at this additional error handling of cppc_cpufreq?
Thanks!

Jie

On 21/08/2024 16:27, Jie Zhan wrote:
> cc linux-arm-kernel
>
> On 19/08/2024 11:51, Jie Zhan wrote:
>> The CPPC performance feedback counters could return 0 when the target
>> cpu
>> is in a deep idle state (e.g. powered off) and those counters are not
>> powered.  cppc_cpufreq_get_rate() returns 0 in this case, triggering two
>> problems:
>>
>> 1. cpufreq_online() gets a false error and doesn't generate a cpufreq
>> policy, which happens in cpufreq_add_dev() when a new cpu device is
>> added.
>> 2. 'cpuinfo_cur_freq' shows '<unknown>'
>>
>> Don't take it as an error and return the frequency corresponding to the
>> desired perf when the feedback counters are 0.
>>
>> Fixes: 6a4fec4f6d30 ("cpufreq: cppc: cppc_cpufreq_get_rate() returns
>> zero in all error cases.")
>> Signed-off-by: Jie Zhan <zhanjie9@hisilicon.com>
>> ---
>>   drivers/cpufreq/cppc_cpufreq.c | 11 +++++++++--
>>   1 file changed, 9 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/cpufreq/cppc_cpufreq.c
>> b/drivers/cpufreq/cppc_cpufreq.c
>> index bafa32dd375d..1c5eb12c1a5a 100644
>> --- a/drivers/cpufreq/cppc_cpufreq.c
>> +++ b/drivers/cpufreq/cppc_cpufreq.c
>> @@ -748,18 +748,25 @@ static unsigned int
>> cppc_cpufreq_get_rate(unsigned int cpu)
>>         ret = cppc_get_perf_ctrs(cpu, &fb_ctrs_t0);
>>       if (ret)
>> -        return 0;
>> +        goto out_err;
>>         udelay(2); /* 2usec delay between sampling */
>>         ret = cppc_get_perf_ctrs(cpu, &fb_ctrs_t1);
>>       if (ret)
>> -        return 0;
>> +        goto out_err;
>>         delivered_perf = cppc_perf_from_fbctrs(cpu_data, &fb_ctrs_t0,
>>                              &fb_ctrs_t1);
>>         return cppc_perf_to_khz(&cpu_data->perf_caps, delivered_perf);
>> +
>> +out_err:
>> +    if (ret == -EFAULT)
>> +        return cppc_perf_to_khz(&cpu_data->perf_caps,
>> +                    cpu_data->perf_ctrls.desired_perf);
>> +
>> +    return 0;
>>   }
>>     static int cppc_cpufreq_set_boost(struct cpufreq_policy *policy,
>> int state)
>