Re: [PATCH v10 15/15] OPTIONAL: cpufreq: dt: Register an Energy Model

[Matthias Kaehlcke <mka@chromium.org>]

Hi Quentin,

On Mon, Dec 03, 2018 at 09:56:28AM +0000, Quentin Perret wrote:
> *******************************************************************
> * This patch illustrates the usage of the newly introduced Energy *
> * Model framework and isn't supposed to be merged as-is.          *
> *******************************************************************
> 
> The Energy Model framework provides an API to register the active power
> of CPUs. Call this API from the cpufreq-dt driver with an estimation
> of the power as P = C * V^2 * f with C, V, and f respectively the
> capacitance of the CPU and the voltage and frequency of the OPP.
> 
> The CPU capacitance is read from the "dynamic-power-coefficient" DT
> binding (originally introduced for thermal/IPA), and the voltage and
> frequency values from PM_OPP.
> 
> Cc: "Rafael J. Wysocki" <rjw@rjwysocki.net>
> Cc: Viresh Kumar <viresh.kumar@linaro.org>
> Signed-off-by: Quentin Perret <quentin.perret@arm.com>
> ---
>  drivers/cpufreq/cpufreq-dt.c | 48 +++++++++++++++++++++++++++++++++++-
>  1 file changed, 47 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/cpufreq/cpufreq-dt.c b/drivers/cpufreq/cpufreq-dt.c
> index e58bfcb1169e..4cfef5554d86 100644
> --- a/drivers/cpufreq/cpufreq-dt.c
> +++ b/drivers/cpufreq/cpufreq-dt.c
> @@ -16,6 +16,7 @@
>  #include <linux/cpu_cooling.h>
>  #include <linux/cpufreq.h>
>  #include <linux/cpumask.h>
> +#include <linux/energy_model.h>
>  #include <linux/err.h>
>  #include <linux/module.h>
>  #include <linux/of.h>
> @@ -150,8 +151,50 @@ static int resources_available(void)
>  	return 0;
>  }
>  
> +static int __maybe_unused of_est_power(unsigned long *mW, unsigned long *KHz,
> +				       int cpu)
> +{
> +	unsigned long mV, Hz, MHz;
> +	struct device *cpu_dev;
> +	struct dev_pm_opp *opp;
> +	struct device_node *np;
> +	u32 cap;
> +	u64 tmp;
> +
> +	cpu_dev = get_cpu_device(cpu);
> +	if (!cpu_dev)
> +		return -ENODEV;
> +
> +	np = of_node_get(cpu_dev->of_node);
> +	if (!np)
> +		return -EINVAL;
> +
> +	if (of_property_read_u32(np, "dynamic-power-coefficient", &cap))
> +		return -EINVAL;
> +
> +	Hz = *KHz * 1000;
> +	opp = dev_pm_opp_find_freq_ceil(cpu_dev, &Hz);
> +	if (IS_ERR(opp))
> +		return -EINVAL;
> +
> +	mV = dev_pm_opp_get_voltage(opp) / 1000;
> +	dev_pm_opp_put(opp);
> +	if (!mV)
> +		return -EINVAL;
> +
> +	MHz = Hz / 1000000;
> +	tmp = (u64)cap * mV * mV * MHz;
> +	do_div(tmp, 1000000000);
> +
> +	*mW = (unsigned long)tmp;
> +	*KHz = Hz / 1000;
> +
> +	return 0;
> +}
> +
>  static int cpufreq_init(struct cpufreq_policy *policy)
>  {
> +	struct em_data_callback em_cb = EM_DATA_CB(of_est_power);
>  	struct cpufreq_frequency_table *freq_table;
>  	struct opp_table *opp_table = NULL;
>  	struct private_data *priv;
> @@ -160,7 +203,7 @@ static int cpufreq_init(struct cpufreq_policy *policy)
>  	unsigned int transition_latency;
>  	bool fallback = false;
>  	const char *name;
> -	int ret;
> +	int ret, nr_opp;
>  
>  	cpu_dev = get_cpu_device(policy->cpu);
>  	if (!cpu_dev) {
> @@ -237,6 +280,7 @@ static int cpufreq_init(struct cpufreq_policy *policy)
>  		ret = -EPROBE_DEFER;
>  		goto out_free_opp;
>  	}
> +	nr_opp = ret;
>  
>  	if (fallback) {
>  		cpumask_setall(policy->cpus);
> @@ -280,6 +324,8 @@ static int cpufreq_init(struct cpufreq_policy *policy)
>  	policy->cpuinfo.transition_latency = transition_latency;
>  	policy->dvfs_possible_from_any_cpu = true;
>  
> +	em_register_perf_domain(policy->cpus, nr_opp, &em_cb);

Shouldn't there also be a function to unregister a perf domain to be
called from cpufreq_exit()?

->exit() is called on suspend when the CPUs are taken offline, and
->init() on resume, hence em_register_perf_domain() is called multiple
times, but without doing any cleanup.

Cheers

Matthias