linux-kernel - Re: [PATCH v3] cpufreq: tegra194: get consistent cpuinfo_cur

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Message-ID: <c56983dc-dc45-3e8c-a67c-14d7d09464ae@nvidia.com>
Date:   Tue, 27 Oct 2020 11:46:32 +0530
From:   Sumit Gupta <sumitg@...dia.com>
To:     <rjw@...ysocki.net>, <viresh.kumar@...aro.org>,
        <sudeep.holla@....com>, <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>
CC:     <bbasu@...dia.com>, <ksitaraman@...dia.com>,
        Sumit Gupta <sumitg@...dia.com>
Subject: Re: [PATCH v3] cpufreq: tegra194: get consistent cpuinfo_cur_freq

Ping.

> 
> 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>
> ---
> 
> Sending only this patch as other patch not required after the change
> to convert 'pr_warn' to 'pr_info' in cpufreq core for unlisted freq.
> Changelog
> v1[2] -> v3:
> - Removed unwanted checks for cpu_online and max cluster number
> - Used WARN_ON_ONCE to avoid print flooding.
> 
> v1[1] -> v2:
> - Minor changes to improve comments and reduce debug prints.
> - Get freq table from cluster specific data instead of policy.
> 
> [2] https://marc.info/?l=linux-tegra&m=160216218511280&w=2
> [1] https://marc.info/?l=linux-arm-kernel&m=160028821117535&w=2
> 
>   drivers/cpufreq/tegra194-cpufreq.c | 62 ++++++++++++++++++++++++++++++++------
>   1 file changed, 53 insertions(+), 9 deletions(-)
> 
> diff --git a/drivers/cpufreq/tegra194-cpufreq.c b/drivers/cpufreq/tegra194-cpufreq.c
> index e1d931c..7901587 100644
> --- a/drivers/cpufreq/tegra194-cpufreq.c
> +++ b/drivers/cpufreq/tegra194-cpufreq.c
> @@ -180,9 +180,61 @@ 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 tegra194_cpufreq_data *data = cpufreq_get_driver_data();
> +       struct cpufreq_frequency_table *pos;
> +       unsigned int rate;
> +       u64 ndiv;
> +       int ret;
> +       u32 cl;
> +
> +       smp_call_function_single(cpu, get_cpu_cluster, &cl, true);
> +
> +       /* reconstruct actual cpu freq using counters */
> +       rate = tegra194_get_speed_common(cpu, US_DELAY);
> +
> +       /* get last written ndiv value */
> +       ret = smp_call_function_single(cpu, get_cpu_ndiv, &ndiv, true);
> +       if (WARN_ON_ONCE(ret))
> +               return rate;
> +
> +       /*
> +        * If the reconstructed frequency has acceptable delta from
> +        * 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, data->tables[cl]) {
> +               if (pos->driver_data != ndiv)
> +                       continue;
> +
> +               if (abs(pos->frequency - rate) > 115200) {
> +                       pr_warn("cpufreq: cpu%d,cur:%u,set:%u,set ndiv:%llu\n",
> +                               cpu, rate, pos->frequency, ndiv);
> +               } else {
> +                       rate = pos->frequency;
> +               }
> +               break;
> +       }
> +       return rate;
>   }
> 
>   static int tegra194_cpufreq_init(struct cpufreq_policy *policy)
> @@ -209,14 +261,6 @@ 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
>