Re: [PATCH v3 1/5] PM / OPP: Introduce a power estimation helper

[Sudeep Holla <sudeep.holla@arm.com>]

On Fri, Feb 01, 2019 at 09:30:57AM +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       | 96 ++++++++++++++++++++++++++++++++++++++++++
>  include/linux/pm_opp.h |  6 +++
>  2 files changed, 102 insertions(+)
> 
> diff --git a/drivers/opp/of.c b/drivers/opp/of.c
> index 06f0f632ec47..4bde13d94dc2 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 +1048,98 @@ 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
> + * @nr_opp	: Number of OPPs to register in the Energy Model
> + *
> + * 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, int nr_opp)
> +{
> +	struct em_data_callback em_cb = EM_DATA_CB(_get_cpu_power);
> +	int ret, cpu = cpumask_first(cpus);
> +	struct device *cpu_dev;
> +	struct device_node *np;
> +	u32 cap;
> +
> +	cpu_dev = get_cpu_device(cpu);
> +	if (!cpu_dev)
> +		return;
> +
> +	np = of_node_get(cpu_dev->of_node);
> +	if (!np)
> +		return;
> +

Does it make sense to add the check for OPP count here. You need not pass
that as parameter. Just makes one less thing to check in new drivers adding
this support. Thoughts ?

--
Regards,
Sudeep

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