Re: [PATCH v4 1/5] PM / OPP: Introduce a power estimation helper

[Matthias Kaehlcke <mka@chromium.org>]

On Mon, Feb 04, 2019 at 11:09:48AM +0000, Quentin Perret wrote:
> The Energy Model (EM) framework provides an API to let drivers register
> the active power of CPUs. The drivers are expected to provide a callback
> method which estimates the power consumed by a CPU at each available
> performance levels. How exactly this should be implemented, however,
> depends on the platform.
> 
> On some systems, PM_OPP knows the voltage and frequency at which CPUs
> can run. When coupled with the CPU 'capacitance' (as provided by the
> 'dynamic-power-coefficient' devicetree binding), it is possible to
> estimate the dynamic power consumption of a CPU as P = C * V^2 * f, with
> C its capacitance and V and f respectively the voltage and frequency of
> the OPP. The Intelligent Power Allocator (IPA) thermal governor already
> implements that estimation method, in the thermal framework.
> 
> However, this power estimation method can be applied to any platform
> where all the parameters are known (C, V and f), and not only those
> suffering thermal issues. As such, the code implementing this feature
> can be re-used to also populate the EM framework now used by EAS.
> 
> As a first step, introduce in PM_OPP a helper function which CPUFreq
> drivers can use to register into the EM framework. This duplicates the
> power estimation done in IPA until it can be migrated to using the EM
> framework. This will be done later, once the EM framework has support
> for at least all platforms currently supported by IPA.
> 
> Signed-off-by: Quentin Perret <quentin.perret@arm.com>
> Tested-by: Matthias Kaehlcke <mka@chromium.org>
> ---
>  drivers/opp/of.c       | 99 ++++++++++++++++++++++++++++++++++++++++++
>  include/linux/pm_opp.h |  6 +++
>  2 files changed, 105 insertions(+)
> 
> diff --git a/drivers/opp/of.c b/drivers/opp/of.c
> index 06f0f632ec47..cd58959e5158 100644
> --- a/drivers/opp/of.c
> +++ b/drivers/opp/of.c
> @@ -20,6 +20,7 @@
>  #include <linux/pm_domain.h>
>  #include <linux/slab.h>
>  #include <linux/export.h>
> +#include <linux/energy_model.h>
>  
>  #include "opp.h"
>  
> @@ -1047,3 +1048,101 @@ struct device_node *dev_pm_opp_get_of_node(struct dev_pm_opp *opp)
>  	return of_node_get(opp->np);
>  }
>  EXPORT_SYMBOL_GPL(dev_pm_opp_get_of_node);
> +
> +/*
> + * Callback function provided to the Energy Model framework upon registration.
> + * This computes the power estimated by @CPU at @kHz if it is the frequency
> + * of an existing OPP, or at the frequency of the first OPP above @kHz otherwise
> + * (see dev_pm_opp_find_freq_ceil()). This function updates @kHz to the ceiled
> + * frequency and @mW to the associated power. The power is estimated as
> + * P = C * V^2 * f with C being the CPU's capacitance and V and f respectively
> + * the voltage and frequency of the OPP.
> + *
> + * Returns -ENODEV if the CPU device cannot be found, -EINVAL if the power
> + * calculation failed because of missing parameters, 0 otherwise.
> + */
> +static int __maybe_unused _get_cpu_power(unsigned long *mW, unsigned long *kHz,
> +					 int cpu)
> +{
> +	struct device *cpu_dev;
> +	struct dev_pm_opp *opp;
> +	struct device_node *np;
> +	unsigned long mV, Hz;
> +	u32 cap;
> +	u64 tmp;
> +	int ret;
> +
> +	cpu_dev = get_cpu_device(cpu);
> +	if (!cpu_dev)
> +		return -ENODEV;
> +
> +	np = of_node_get(cpu_dev->of_node);
> +	if (!np)
> +		return -EINVAL;
> +
> +	ret = of_property_read_u32(np, "dynamic-power-coefficient", &cap);
> +	of_node_put(np);
> +	if (ret)
> +		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;
> +
> +	tmp = (u64)cap * mV * mV * (Hz / 1000000);
> +	do_div(tmp, 1000000000);
> +
> +	*mW = (unsigned long)tmp;
> +	*kHz = Hz / 1000;
> +
> +	return 0;
> +}
> +
> +/**
> + * dev_pm_opp_of_register_em() - Attempt to register an Energy Model
> + * @cpus	: CPUs for which an Energy Model has to be registered
> + *
> + * This checks whether the "dynamic-power-coefficient" devicetree property has
> + * been specified, and tries to register an Energy Model with it if it has.
> + */
> +void dev_pm_opp_of_register_em(struct cpumask *cpus)
> +{
> +	struct em_data_callback em_cb = EM_DATA_CB(_get_cpu_power);
> +	int ret, nr_opp, cpu = cpumask_first(cpus);
> +	struct device *cpu_dev;
> +	struct device_node *np;
> +	u32 cap;
> +
> +	cpu_dev = get_cpu_device(cpu);
> +	if (!cpu_dev)
> +		return;
> +
> +	nr_opp = dev_pm_opp_get_opp_count(cpu_dev);
> +	if (nr_opp <= 0)
> +		return;
> +
> +	np = of_node_get(cpu_dev->of_node);
> +	if (!np)
> +		return;
> +
> +	/*
> +	 * Register an EM only if the 'dynamic-power-coefficient' property is
> +	 * set in devicetree. It is assumed the voltage values are known if that
> +	 * property is set since it is useless otherwise. If voltages are not
> +	 * known, just let the EM registration fail with an error to alert the
> +	 * user about the inconsistent configuration.
> +	 */
> +	ret = of_property_read_u32(np, "dynamic-power-coefficient", &cap);
> +	of_node_put(np);
> +	if (ret || !cap)
> +		return;
> +
> +	em_register_perf_domain(cpus, nr_opp, &em_cb);
> +}
> +EXPORT_SYMBOL_GPL(dev_pm_opp_of_register_em);
> diff --git a/include/linux/pm_opp.h b/include/linux/pm_opp.h
> index b895f4e79868..c9c76310865a 100644
> --- a/include/linux/pm_opp.h
> +++ b/include/linux/pm_opp.h
> @@ -327,6 +327,7 @@ int dev_pm_opp_of_get_sharing_cpus(struct device *cpu_dev, struct cpumask *cpuma
>  struct device_node *dev_pm_opp_of_get_opp_desc_node(struct device *dev);
>  struct device_node *dev_pm_opp_get_of_node(struct dev_pm_opp *opp);
>  int of_get_required_opp_performance_state(struct device_node *np, int index);
> +void dev_pm_opp_of_register_em(struct cpumask *cpus);
>  #else
>  static inline int dev_pm_opp_of_add_table(struct device *dev)
>  {
> @@ -365,6 +366,11 @@ static inline struct device_node *dev_pm_opp_get_of_node(struct dev_pm_opp *opp)
>  {
>  	return NULL;
>  }
> +
> +static inline void dev_pm_opp_of_register_em(struct cpumask *cpus)
> +{
> +}
> +
>  static inline int of_get_required_opp_performance_state(struct device_node *np, int index)
>  {
>  	return -ENOTSUPP;

There is the option to remove the OPP check from the cpufreq drivers
and instead return an error from dev_pm_opp_of_register_em(), but with
the more complex error handling it might be more hassle than it's
worth.

Reviewed-by: Matthias Kaehlcke <mka@chromium.org>