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

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Message-ID: <20201005044621.t3stylpbsvzhxtyr@vireshk-i7>
Date:   Mon, 5 Oct 2020 10:16:21 +0530
From:   Viresh Kumar <viresh.kumar@...aro.org>
To:     Sumit Gupta <sumitg@...dia.com>
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
Subject: Re: [Patch 1/2] cpufreq: tegra194: get consistent cpuinfo_cur_freq

On 16-09-20, 22:41, Sumit Gupta wrote:
> 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.

> +
> +	/* 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.

> +	 * 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.

> +		} 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