linux-kernel - Re: [PATCH 2/3] cpufreq: Implement freq-constraint callback

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Date:   Thu, 17 Jan 2019 17:46:32 -0800
From:   Matthias Kaehlcke <mka@...omium.org>
To:     Viresh Kumar <viresh.kumar@...aro.org>
Cc:     Rafael Wysocki <rjw@...ysocki.net>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-pm@...r.kernel.org,
        Vincent Guittot <vincent.guittot@...aro.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/3] cpufreq: Implement freq-constraint callback

On Fri, Jan 11, 2019 at 02:48:35PM +0530, Viresh Kumar wrote:
> This implements the frequency constraint callback and registers it with
> the freq-constraint framework whenever a policy is created. On policy
> removal the callback is unregistered.
> 
> The constraints are also taken into consideration in
> cpufreq_set_policy().
> 
> No constraints are added until now though.

nit: 'for now'?

> Signed-off-by: Viresh Kumar <viresh.kumar@...aro.org>
> ---
>  drivers/cpufreq/Kconfig   |  1 +
>  drivers/cpufreq/cpufreq.c | 44 ++++++++++++++++++++++++++++++++++++++++++++
>  2 files changed, 45 insertions(+)
> 
> diff --git a/drivers/cpufreq/Kconfig b/drivers/cpufreq/Kconfig
> index 608af20a3494..2c2842cf2734 100644
> --- a/drivers/cpufreq/Kconfig
> +++ b/drivers/cpufreq/Kconfig
> @@ -2,6 +2,7 @@ menu "CPU Frequency scaling"
>  
>  config CPU_FREQ
>  	bool "CPU Frequency scaling"
> +	select DEVICE_FREQ_CONSTRAINT
>  	select SRCU
>  	help
>  	  CPU Frequency scaling allows you to change the clock speed of 
> diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
> index a8fa684f5f90..63028612d011 100644
> --- a/drivers/cpufreq/cpufreq.c
> +++ b/drivers/cpufreq/cpufreq.c
> @@ -21,6 +21,7 @@
>  #include <linux/cpufreq.h>
>  #include <linux/delay.h>
>  #include <linux/device.h>
> +#include <linux/freq_constraint.h>
>  #include <linux/init.h>
>  #include <linux/kernel_stat.h>
>  #include <linux/module.h>
> @@ -1163,6 +1164,7 @@ static void cpufreq_policy_free(struct cpufreq_policy *policy)
>  		per_cpu(cpufreq_cpu_data, cpu) = NULL;
>  	write_unlock_irqrestore(&cpufreq_driver_lock, flags);
>  
> +	freq_constraint_remove_cpumask_callback(policy->related_cpus);
>  	cpufreq_policy_put_kobj(policy);
>  	free_cpumask_var(policy->real_cpus);
>  	free_cpumask_var(policy->related_cpus);
> @@ -1170,6 +1172,24 @@ static void cpufreq_policy_free(struct cpufreq_policy *policy)
>  	kfree(policy);
>  }
>  
> +static void freq_constraint_callback(void *param)
> +{
> +	struct cpufreq_policy *policy = param;
> +	struct cpufreq_policy new_policy = *policy;
> +
> +	new_policy.min = policy->user_policy.min;
> +	new_policy.max = policy->user_policy.max;
> +
> +	down_write(&policy->rwsem);
> +	if (policy_is_inactive(policy))
> +		goto unlock;
> +
> +	cpufreq_set_policy(policy, &new_policy);
> +
> +unlock:
> +	up_write(&policy->rwsem);
> +}
> +
>  static int cpufreq_online(unsigned int cpu)
>  {
>  	struct cpufreq_policy *policy;
> @@ -1236,6 +1256,14 @@ static int cpufreq_online(unsigned int cpu)
>  			per_cpu(cpufreq_cpu_data, j) = policy;
>  			add_cpu_dev_symlink(policy, j);
>  		}
> +
> +		ret = freq_constraint_set_cpumask_callback(policy->related_cpus,
> +					freq_constraint_callback, policy);
> +		if (ret) {
> +			pr_err("Failed to set freq-constraints: %d (%*pbl)\n",
> +			       ret, cpumask_pr_args(policy->cpus));
> +			goto out_destroy_policy;
> +		}
>  	} else {
>  		policy->min = policy->user_policy.min;
>  		policy->max = policy->user_policy.max;
> @@ -2198,6 +2226,8 @@ static int cpufreq_set_policy(struct cpufreq_policy *policy,
>  				struct cpufreq_policy *new_policy)
>  {
>  	struct cpufreq_governor *old_gov;
> +	struct device *cpu_dev = get_cpu_device(policy->cpu);
> +	unsigned long fc_min, fc_max;
>  	int ret;
>  
>  	pr_debug("setting new policy for CPU %u: %u - %u kHz\n",
> @@ -2217,6 +2247,20 @@ static int cpufreq_set_policy(struct cpufreq_policy *policy,
>  	if (ret)
>  		return ret;
>  
> +	ret = freq_constraints_get(cpu_dev, &fc_min, &fc_max);
> +	if (ret) {
> +		dev_err(cpu_dev, "cpufreq: Failed to get freq-constraints\n");
> +	} else {
> +		if (fc_min > new_policy->min)
> +			new_policy->min = fc_min;
> +		if (fc_max < new_policy->max)
> +			new_policy->max = fc_max;
> +	}

nit: for if/else constructs with a typical and an 'exception' case
IMO it is usually more readable when the normal case is handled in the
'if' branch (first) and the exception in 'else'.

Cheers

Matthias