linux-kernel - Re: [Patch 1/2] cpufreq: tegra194: get consistent cpuinfo_cur

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Message-ID: <69929ea0-0304-3bbe-fd33-40f50791a0ec@nvidia.com>
Date:   Tue, 6 Oct 2020 00:10:15 +0530
From:   Sumit Gupta <sumitg@...dia.com>
To:     Viresh Kumar <viresh.kumar@...aro.org>
CC:     <rjw@...ysocki.net>, <thierry.reding@...il.com>,
        <jonathanh@...dia.com>, <linux-pm@...r.kernel.org>,
        <linux-tegra@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>, <ksitaraman@...dia.com>,
        <bbasu@...dia.com>, Sumit Gupta <sumitg@...dia.com>
Subject: Re: [Patch 1/2] cpufreq: tegra194: get consistent cpuinfo_cur_freq


>> Frequency returned by 'cpuinfo_cur_freq' using counters is not fixed
>> and keeps changing slightly. This change returns a consistent value
>> from freq_table. If the reconstructed frequency has acceptable delta
>> from the last written value, then return the frequency corresponding
>> to the last written ndiv value from freq_table. Otherwise, print a
>> warning and return the reconstructed freq.
>>
>> Signed-off-by: Sumit Gupta <sumitg@...dia.com>
>> ---
>>   drivers/cpufreq/tegra194-cpufreq.c | 66 ++++++++++++++++++++++++++++++++------
>>   1 file changed, 57 insertions(+), 9 deletions(-)
>>
>> diff --git a/drivers/cpufreq/tegra194-cpufreq.c b/drivers/cpufreq/tegra194-cpufreq.c
>> index e1d931c..d5b608d 100644
>> --- a/drivers/cpufreq/tegra194-cpufreq.c
>> +++ b/drivers/cpufreq/tegra194-cpufreq.c
>> @@ -180,9 +180,65 @@ static unsigned int tegra194_get_speed_common(u32 cpu, u32 delay)
>>        return (rate_mhz * KHZ); /* in KHz */
>>   }
>>
>> +static void get_cpu_ndiv(void *ndiv)
>> +{
>> +     u64 ndiv_val;
>> +
>> +     asm volatile("mrs %0, s3_0_c15_c0_4" : "=r" (ndiv_val) : );
>> +
>> +     *(u64 *)ndiv = ndiv_val;
>> +}
>> +
>> +static void set_cpu_ndiv(void *data)
>> +{
>> +     struct cpufreq_frequency_table *tbl = data;
>> +     u64 ndiv_val = (u64)tbl->driver_data;
>> +
>> +     asm volatile("msr s3_0_c15_c0_4, %0" : : "r" (ndiv_val));
>> +}
>> +
>>   static unsigned int tegra194_get_speed(u32 cpu)
>>   {
>> -     return tegra194_get_speed_common(cpu, US_DELAY);
>> +     struct cpufreq_frequency_table *table, *pos;
>> +     struct cpufreq_policy policy;
>> +     unsigned int rate;
>> +     u64 ndiv;
>> +     int err;
>> +
>> +     cpufreq_get_policy(&policy, cpu);
>> +     table = policy.freq_table;
> 
> Maybe getting freq-table from cluster specific data would be better/faster.
> 
will do the change in next patch version.

>> +
>> +     /* reconstruct actual cpu freq using counters*/
>> +     rate = tegra194_get_speed_common(cpu, US_DELAY);
>> +
>> +     /* get last written ndiv value*/
>> +     err = smp_call_function_single(cpu, get_cpu_ndiv, &ndiv, true);
>> +     if (err) {
>> +             pr_err("cpufreq: Failed to get ndiv for CPU%d, ret:%d\n",
>> +                    cpu, err);
>> +             return rate;
>> +     }
>> +
>> +     /* if the reconstructed frequency has acceptable delta from
> 
> Both have got the multi-line comments wrong. Format is wrong and every sentence
> needs to start with a capital letter.
> 
will correct.

>> +      * the last written value, then return freq corresponding
>> +      * to the last written ndiv value from freq_table. This is
>> +      * done to return consistent value.
>> +      */
>> +     cpufreq_for_each_valid_entry(pos, table) {
>> +             if (pos->driver_data != ndiv)
>> +                     continue;
>> +
>> +             if (abs(pos->frequency - rate) > 115200) {
>> +                     pr_warn("cpufreq: high delta (%d) on CPU%d\n",
>> +                             abs(pos->frequency - rate), cpu);
>> +                     pr_warn("cpufreq: cur:%u, set:%u, set ndiv:%llu\n",
>> +                             rate, pos->frequency, ndiv);
> 
> Both of these can be merged in a single line I think. There is no need to print
> delta as you already print both the frequencies.
> 
Will do this also in next patch version.

>> +             } else {
>> +                     rate = pos->frequency;
>> +             }
>> +             break;
>> +     }
>> +     return rate;
>>   }
>>
>>   static int tegra194_cpufreq_init(struct cpufreq_policy *policy)
>> @@ -209,14 +265,6 @@ static int tegra194_cpufreq_init(struct cpufreq_policy *policy)
>>        return 0;
>>   }
>>
>> -static void set_cpu_ndiv(void *data)
>> -{
>> -     struct cpufreq_frequency_table *tbl = data;
>> -     u64 ndiv_val = (u64)tbl->driver_data;
>> -
>> -     asm volatile("msr s3_0_c15_c0_4, %0" : : "r" (ndiv_val));
>> -}
>> -
>>   static int tegra194_cpufreq_set_target(struct cpufreq_policy *policy,
>>                                       unsigned int index)
>>   {
>> --
>> 2.7.4
> 
> --
> viresh
>