[v5,2/5] OPP: refactor dev_pm_opp_of_register_em() and update related drivers
diff mbox series

Message ID 20200318114548.19916-3-lukasz.luba@arm.com
State New
Headers show
Series
  • Add support for devices in the Energy Model
Related show

Commit Message

Lukasz Luba March 18, 2020, 11:45 a.m. UTC
The Energy Model framework supports both: CPUs and devfreq devices. Drop
the CPU specific interface with cpumask and add struct device. Add also a
return value. This new interface provides easy way to create a simple
Energy Model, which then might be used in i.e. thermal subsystem.

Signed-off-by: Lukasz Luba <lukasz.luba@arm.com>
---
 drivers/cpufreq/cpufreq-dt.c           |  2 +-
 drivers/cpufreq/imx6q-cpufreq.c        |  2 +-
 drivers/cpufreq/mediatek-cpufreq.c     |  2 +-
 drivers/cpufreq/omap-cpufreq.c         |  2 +-
 drivers/cpufreq/qcom-cpufreq-hw.c      |  2 +-
 drivers/cpufreq/scpi-cpufreq.c         |  2 +-
 drivers/cpufreq/vexpress-spc-cpufreq.c |  2 +-
 drivers/opp/of.c                       | 71 ++++++++++++++++----------
 include/linux/pm_opp.h                 | 15 +++++-
 9 files changed, 65 insertions(+), 35 deletions(-)

Comments

Lukasz Luba April 1, 2020, 7:19 a.m. UTC | #1
On 3/18/20 11:45 AM, Lukasz Luba wrote:
> The Energy Model framework supports both: CPUs and devfreq devices. Drop
> the CPU specific interface with cpumask and add struct device. Add also a
> return value. This new interface provides easy way to create a simple
> Energy Model, which then might be used in i.e. thermal subsystem.
> 
> Signed-off-by: Lukasz Luba <lukasz.luba@arm.com>
> ---
>   drivers/cpufreq/cpufreq-dt.c           |  2 +-
>   drivers/cpufreq/imx6q-cpufreq.c        |  2 +-
>   drivers/cpufreq/mediatek-cpufreq.c     |  2 +-
>   drivers/cpufreq/omap-cpufreq.c         |  2 +-
>   drivers/cpufreq/qcom-cpufreq-hw.c      |  2 +-
>   drivers/cpufreq/scpi-cpufreq.c         |  2 +-
>   drivers/cpufreq/vexpress-spc-cpufreq.c |  2 +-
>   drivers/opp/of.c                       | 71 ++++++++++++++++----------
>   include/linux/pm_opp.h                 | 15 +++++-
>   9 files changed, 65 insertions(+), 35 deletions(-)


Gentle ping.

Viresh could you have a look at it?

Regards,
Lukasz
Daniel Lezcano April 3, 2020, 4:21 p.m. UTC | #2
On 18/03/2020 12:45, Lukasz Luba wrote:
> The Energy Model framework supports both: CPUs and devfreq devices. Drop
> the CPU specific interface with cpumask and add struct device. Add also a
> return value. This new interface provides easy way to create a simple
> Energy Model, which then might be used in i.e. thermal subsystem.

This patch contains too many different changes.

There are fixes and traces added in addition to a function prototype change.

Please provide patches separated by logical changes.

If the cpumask is extracted in the underlying function
em_register_perf_domain() as suggested in the previous patch 1/5,
dev_pm_opp_of_register_em() can be struct device centric only.

> Signed-off-by: Lukasz Luba <lukasz.luba@arm.com>
> ---
>  drivers/cpufreq/cpufreq-dt.c           |  2 +-
>  drivers/cpufreq/imx6q-cpufreq.c        |  2 +-
>  drivers/cpufreq/mediatek-cpufreq.c     |  2 +-
>  drivers/cpufreq/omap-cpufreq.c         |  2 +-
>  drivers/cpufreq/qcom-cpufreq-hw.c      |  2 +-
>  drivers/cpufreq/scpi-cpufreq.c         |  2 +-
>  drivers/cpufreq/vexpress-spc-cpufreq.c |  2 +-
>  drivers/opp/of.c                       | 71 ++++++++++++++++----------
>  include/linux/pm_opp.h                 | 15 +++++-
>  9 files changed, 65 insertions(+), 35 deletions(-)
> 
> diff --git a/drivers/cpufreq/cpufreq-dt.c b/drivers/cpufreq/cpufreq-dt.c
> index 26fe8dfb9ce6..f9f03fd49b83 100644
> --- a/drivers/cpufreq/cpufreq-dt.c
> +++ b/drivers/cpufreq/cpufreq-dt.c
> @@ -275,7 +275,7 @@ static int cpufreq_init(struct cpufreq_policy *policy)
>  	policy->cpuinfo.transition_latency = transition_latency;
>  	policy->dvfs_possible_from_any_cpu = true;
>  
> -	dev_pm_opp_of_register_em(policy->cpus);
> +	dev_pm_opp_of_register_em(cpu_dev, policy->cpus);
>  
>  	return 0;
>  
> diff --git a/drivers/cpufreq/imx6q-cpufreq.c b/drivers/cpufreq/imx6q-cpufreq.c
> index 285b8e9aa185..9764abf17ce3 100644
> --- a/drivers/cpufreq/imx6q-cpufreq.c
> +++ b/drivers/cpufreq/imx6q-cpufreq.c
> @@ -193,7 +193,7 @@ static int imx6q_cpufreq_init(struct cpufreq_policy *policy)
>  	policy->clk = clks[ARM].clk;
>  	cpufreq_generic_init(policy, freq_table, transition_latency);
>  	policy->suspend_freq = max_freq;
> -	dev_pm_opp_of_register_em(policy->cpus);
> +	dev_pm_opp_of_register_em(cpu_dev, policy->cpus);
>  
>  	return 0;
>  }
> diff --git a/drivers/cpufreq/mediatek-cpufreq.c b/drivers/cpufreq/mediatek-cpufreq.c
> index 0c98dd08273d..7d1212c9b7c8 100644
> --- a/drivers/cpufreq/mediatek-cpufreq.c
> +++ b/drivers/cpufreq/mediatek-cpufreq.c
> @@ -448,7 +448,7 @@ static int mtk_cpufreq_init(struct cpufreq_policy *policy)
>  	policy->driver_data = info;
>  	policy->clk = info->cpu_clk;
>  
> -	dev_pm_opp_of_register_em(policy->cpus);
> +	dev_pm_opp_of_register_em(info->cpu_dev, policy->cpus);
>  
>  	return 0;
>  }
> diff --git a/drivers/cpufreq/omap-cpufreq.c b/drivers/cpufreq/omap-cpufreq.c
> index 8d14b42a8c6f..3694bb030df3 100644
> --- a/drivers/cpufreq/omap-cpufreq.c
> +++ b/drivers/cpufreq/omap-cpufreq.c
> @@ -131,7 +131,7 @@ static int omap_cpu_init(struct cpufreq_policy *policy)
>  
>  	/* FIXME: what's the actual transition time? */
>  	cpufreq_generic_init(policy, freq_table, 300 * 1000);
> -	dev_pm_opp_of_register_em(policy->cpus);
> +	dev_pm_opp_of_register_em(mpu_dev, policy->cpus);
>  
>  	return 0;
>  }
> diff --git a/drivers/cpufreq/qcom-cpufreq-hw.c b/drivers/cpufreq/qcom-cpufreq-hw.c
> index fc92a8842e25..0a04b6f03b9a 100644
> --- a/drivers/cpufreq/qcom-cpufreq-hw.c
> +++ b/drivers/cpufreq/qcom-cpufreq-hw.c
> @@ -238,7 +238,7 @@ static int qcom_cpufreq_hw_cpu_init(struct cpufreq_policy *policy)
>  		goto error;
>  	}
>  
> -	dev_pm_opp_of_register_em(policy->cpus);
> +	dev_pm_opp_of_register_em(cpu_dev, policy->cpus);
>  
>  	policy->fast_switch_possible = true;
>  
> diff --git a/drivers/cpufreq/scpi-cpufreq.c b/drivers/cpufreq/scpi-cpufreq.c
> index 20d1f85d5f5a..b0f5388b8854 100644
> --- a/drivers/cpufreq/scpi-cpufreq.c
> +++ b/drivers/cpufreq/scpi-cpufreq.c
> @@ -167,7 +167,7 @@ static int scpi_cpufreq_init(struct cpufreq_policy *policy)
>  
>  	policy->fast_switch_possible = false;
>  
> -	dev_pm_opp_of_register_em(policy->cpus);
> +	dev_pm_opp_of_register_em(cpu_dev, policy->cpus);
>  
>  	return 0;
>  
> diff --git a/drivers/cpufreq/vexpress-spc-cpufreq.c b/drivers/cpufreq/vexpress-spc-cpufreq.c
> index 83c85d3d67e3..4e8b1dee7c9a 100644
> --- a/drivers/cpufreq/vexpress-spc-cpufreq.c
> +++ b/drivers/cpufreq/vexpress-spc-cpufreq.c
> @@ -450,7 +450,7 @@ static int ve_spc_cpufreq_init(struct cpufreq_policy *policy)
>  	policy->freq_table = freq_table[cur_cluster];
>  	policy->cpuinfo.transition_latency = 1000000; /* 1 ms */
>  
> -	dev_pm_opp_of_register_em(policy->cpus);
> +	dev_pm_opp_of_register_em(cpu_dev, policy->cpus);
>  
>  	if (is_bL_switching_enabled())
>  		per_cpu(cpu_last_req_freq, policy->cpu) =
> diff --git a/drivers/opp/of.c b/drivers/opp/of.c
> index 0efd6cf6d023..f94d095113e7 100644
> --- a/drivers/opp/of.c
> +++ b/drivers/opp/of.c
> @@ -1036,18 +1036,18 @@ 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
> + * This computes the power estimated by @dev 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.
> + * P = C * V^2 * f with C being the device'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.
> + * Returns -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,
> -					 struct device *cpu_dev)
> +static int __maybe_unused _get_power(unsigned long *mW, unsigned long *kHz,
> +				     struct device *dev)
>  {
>  	struct dev_pm_opp *opp;
>  	struct device_node *np;
> @@ -1056,7 +1056,7 @@ static int __maybe_unused _get_cpu_power(unsigned long *mW, unsigned long *kHz,
>  	u64 tmp;
>  	int ret;
>  
> -	np = of_node_get(cpu_dev->of_node);
> +	np = of_node_get(dev->of_node);
>  	if (!np)
>  		return -EINVAL;
>  
> @@ -1066,7 +1066,7 @@ static int __maybe_unused _get_cpu_power(unsigned long *mW, unsigned long *kHz,
>  		return -EINVAL;
>  
>  	Hz = *kHz * 1000;
> -	opp = dev_pm_opp_find_freq_ceil(cpu_dev, &Hz);
> +	opp = dev_pm_opp_find_freq_ceil(dev, &Hz);
>  	if (IS_ERR(opp))
>  		return -EINVAL;
>  
> @@ -1086,30 +1086,38 @@ static int __maybe_unused _get_cpu_power(unsigned long *mW, unsigned long *kHz,
>  
>  /**
>   * dev_pm_opp_of_register_em() - Attempt to register an Energy Model
> - * @cpus	: CPUs for which an Energy Model has to be registered
> + * @dev		: Device for which an Energy Model has to be registered
> + * @cpus	: CPUs for which an Energy Model has to be registered. For
> + *		other type of devices it should be set to NULL.
>   *
>   * This checks whether the "dynamic-power-coefficient" devicetree property has
>   * been specified, and tries to register an Energy Model with it if it has.
> + * Having this property means the voltages are known for OPPs and the EM
> + * might be calculated.
>   */
> -void dev_pm_opp_of_register_em(struct cpumask *cpus)
> +int dev_pm_opp_of_register_em(struct device *dev, 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 em_data_callback em_cb = EM_DATA_CB(_get_power);
>  	struct device_node *np;
> +	int ret, nr_opp;
>  	u32 cap;
>  
> -	cpu_dev = get_cpu_device(cpu);
> -	if (!cpu_dev)
> -		return;
> +	if (IS_ERR_OR_NULL(dev)) {
> +		ret = -EINVAL;
> +		goto failed;
> +	}
>  
> -	nr_opp = dev_pm_opp_get_opp_count(cpu_dev);
> -	if (nr_opp <= 0)
> -		return;
> +	nr_opp = dev_pm_opp_get_opp_count(dev);
> +	if (nr_opp <= 0) {
> +		ret = -EINVAL;
> +		goto failed;
> +	}
>  
> -	np = of_node_get(cpu_dev->of_node);
> -	if (!np)
> -		return;
> +	np = of_node_get(dev->of_node);
> +	if (!np) {
> +		ret = -EINVAL;
> +		goto failed;
> +	}
>  
>  	/*
>  	 * Register an EM only if the 'dynamic-power-coefficient' property is
> @@ -1120,9 +1128,20 @@ void dev_pm_opp_of_register_em(struct cpumask *cpus)
>  	 */
>  	ret = of_property_read_u32(np, "dynamic-power-coefficient", &cap);
>  	of_node_put(np);
> -	if (ret || !cap)
> -		return;
> +	if (ret || !cap) {
> +		dev_dbg(dev, "Couldn't find proper 'dynamic-power-coefficient' in DT\n");
> +		ret = -EINVAL;
> +		goto failed;
> +	}
>  
> -	em_register_perf_domain(cpu_dev, nr_opp, &em_cb, cpus);
> +	ret = em_register_perf_domain(dev, nr_opp, &em_cb, cpus);
> +	if (ret)
> +		goto failed;
> +
> +	return 0;
> +
> +failed:
> +	dev_dbg(dev, "Couldn't register Energy Model %d\n", ret);
> +	return ret;
>  }
>  EXPORT_SYMBOL_GPL(dev_pm_opp_of_register_em);
> diff --git a/include/linux/pm_opp.h b/include/linux/pm_opp.h
> index 747861816f4f..822ff9f52bf7 100644
> --- a/include/linux/pm_opp.h
> +++ b/include/linux/pm_opp.h
> @@ -11,6 +11,7 @@
>  #ifndef __LINUX_OPP_H__
>  #define __LINUX_OPP_H__
>  
> +#include <linux/energy_model.h>
>  #include <linux/err.h>
>  #include <linux/notifier.h>
>  
> @@ -360,7 +361,11 @@ 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);
> +int dev_pm_opp_of_register_em(struct device *dev, struct cpumask *cpus);
> +static inline void dev_pm_opp_of_unregister_em(struct device *dev)
> +{
> +	em_unregister_perf_domain(dev);
> +}
>  #else
>  static inline int dev_pm_opp_of_add_table(struct device *dev)
>  {
> @@ -400,7 +405,13 @@ 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 dev_pm_opp_of_register_em(struct device *dev,
> +					    struct cpumask *cpus)
> +{
> +	return -ENOTSUPP;
> +}
> +
> +static inline void dev_pm_opp_of_unregister_em(struct device *dev)
>  {
>  }
>  
>
Lukasz Luba April 6, 2020, 2:05 p.m. UTC | #3
Hi Daniel,

Thank you for your comments.

On 4/3/20 5:21 PM, Daniel Lezcano wrote:
> On 18/03/2020 12:45, Lukasz Luba wrote:
>> The Energy Model framework supports both: CPUs and devfreq devices. Drop
>> the CPU specific interface with cpumask and add struct device. Add also a
>> return value. This new interface provides easy way to create a simple
>> Energy Model, which then might be used in i.e. thermal subsystem.
> 
> This patch contains too many different changes.

OK, I will create 4 patches:
1) change with new argument in API function:
    void dev_pm_opp_of_register_em(dev, cpumask)
   and updated drivers
2) changes with _get_cpu_power --> _get_power
3) changes adding int return in dev_pm_opp_of_register_em()
    and updating error handling path inside
4) header changes with new dev_pm_opp_of_unregister_em()

> 
> There are fixes and traces added in addition to a function prototype change. >
> Please provide patches separated by logical changes.

I will try to make this API change in a safe way, which
won't break cpufreq drivers compilation.

> 
> If the cpumask is extracted in the underlying function
> em_register_perf_domain() as suggested in the previous patch 1/5,
> dev_pm_opp_of_register_em() can be struct device centric only.

That would be ideal situation but unfortunately not possible to
implement (as responded in 1/5).

Regards,
Lukasz

Patch
diff mbox series

diff --git a/drivers/cpufreq/cpufreq-dt.c b/drivers/cpufreq/cpufreq-dt.c
index 26fe8dfb9ce6..f9f03fd49b83 100644
--- a/drivers/cpufreq/cpufreq-dt.c
+++ b/drivers/cpufreq/cpufreq-dt.c
@@ -275,7 +275,7 @@  static int cpufreq_init(struct cpufreq_policy *policy)
 	policy->cpuinfo.transition_latency = transition_latency;
 	policy->dvfs_possible_from_any_cpu = true;
 
-	dev_pm_opp_of_register_em(policy->cpus);
+	dev_pm_opp_of_register_em(cpu_dev, policy->cpus);
 
 	return 0;
 
diff --git a/drivers/cpufreq/imx6q-cpufreq.c b/drivers/cpufreq/imx6q-cpufreq.c
index 285b8e9aa185..9764abf17ce3 100644
--- a/drivers/cpufreq/imx6q-cpufreq.c
+++ b/drivers/cpufreq/imx6q-cpufreq.c
@@ -193,7 +193,7 @@  static int imx6q_cpufreq_init(struct cpufreq_policy *policy)
 	policy->clk = clks[ARM].clk;
 	cpufreq_generic_init(policy, freq_table, transition_latency);
 	policy->suspend_freq = max_freq;
-	dev_pm_opp_of_register_em(policy->cpus);
+	dev_pm_opp_of_register_em(cpu_dev, policy->cpus);
 
 	return 0;
 }
diff --git a/drivers/cpufreq/mediatek-cpufreq.c b/drivers/cpufreq/mediatek-cpufreq.c
index 0c98dd08273d..7d1212c9b7c8 100644
--- a/drivers/cpufreq/mediatek-cpufreq.c
+++ b/drivers/cpufreq/mediatek-cpufreq.c
@@ -448,7 +448,7 @@  static int mtk_cpufreq_init(struct cpufreq_policy *policy)
 	policy->driver_data = info;
 	policy->clk = info->cpu_clk;
 
-	dev_pm_opp_of_register_em(policy->cpus);
+	dev_pm_opp_of_register_em(info->cpu_dev, policy->cpus);
 
 	return 0;
 }
diff --git a/drivers/cpufreq/omap-cpufreq.c b/drivers/cpufreq/omap-cpufreq.c
index 8d14b42a8c6f..3694bb030df3 100644
--- a/drivers/cpufreq/omap-cpufreq.c
+++ b/drivers/cpufreq/omap-cpufreq.c
@@ -131,7 +131,7 @@  static int omap_cpu_init(struct cpufreq_policy *policy)
 
 	/* FIXME: what's the actual transition time? */
 	cpufreq_generic_init(policy, freq_table, 300 * 1000);
-	dev_pm_opp_of_register_em(policy->cpus);
+	dev_pm_opp_of_register_em(mpu_dev, policy->cpus);
 
 	return 0;
 }
diff --git a/drivers/cpufreq/qcom-cpufreq-hw.c b/drivers/cpufreq/qcom-cpufreq-hw.c
index fc92a8842e25..0a04b6f03b9a 100644
--- a/drivers/cpufreq/qcom-cpufreq-hw.c
+++ b/drivers/cpufreq/qcom-cpufreq-hw.c
@@ -238,7 +238,7 @@  static int qcom_cpufreq_hw_cpu_init(struct cpufreq_policy *policy)
 		goto error;
 	}
 
-	dev_pm_opp_of_register_em(policy->cpus);
+	dev_pm_opp_of_register_em(cpu_dev, policy->cpus);
 
 	policy->fast_switch_possible = true;
 
diff --git a/drivers/cpufreq/scpi-cpufreq.c b/drivers/cpufreq/scpi-cpufreq.c
index 20d1f85d5f5a..b0f5388b8854 100644
--- a/drivers/cpufreq/scpi-cpufreq.c
+++ b/drivers/cpufreq/scpi-cpufreq.c
@@ -167,7 +167,7 @@  static int scpi_cpufreq_init(struct cpufreq_policy *policy)
 
 	policy->fast_switch_possible = false;
 
-	dev_pm_opp_of_register_em(policy->cpus);
+	dev_pm_opp_of_register_em(cpu_dev, policy->cpus);
 
 	return 0;
 
diff --git a/drivers/cpufreq/vexpress-spc-cpufreq.c b/drivers/cpufreq/vexpress-spc-cpufreq.c
index 83c85d3d67e3..4e8b1dee7c9a 100644
--- a/drivers/cpufreq/vexpress-spc-cpufreq.c
+++ b/drivers/cpufreq/vexpress-spc-cpufreq.c
@@ -450,7 +450,7 @@  static int ve_spc_cpufreq_init(struct cpufreq_policy *policy)
 	policy->freq_table = freq_table[cur_cluster];
 	policy->cpuinfo.transition_latency = 1000000; /* 1 ms */
 
-	dev_pm_opp_of_register_em(policy->cpus);
+	dev_pm_opp_of_register_em(cpu_dev, policy->cpus);
 
 	if (is_bL_switching_enabled())
 		per_cpu(cpu_last_req_freq, policy->cpu) =
diff --git a/drivers/opp/of.c b/drivers/opp/of.c
index 0efd6cf6d023..f94d095113e7 100644
--- a/drivers/opp/of.c
+++ b/drivers/opp/of.c
@@ -1036,18 +1036,18 @@  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
+ * This computes the power estimated by @dev 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.
+ * P = C * V^2 * f with C being the device'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.
+ * Returns -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,
-					 struct device *cpu_dev)
+static int __maybe_unused _get_power(unsigned long *mW, unsigned long *kHz,
+				     struct device *dev)
 {
 	struct dev_pm_opp *opp;
 	struct device_node *np;
@@ -1056,7 +1056,7 @@  static int __maybe_unused _get_cpu_power(unsigned long *mW, unsigned long *kHz,
 	u64 tmp;
 	int ret;
 
-	np = of_node_get(cpu_dev->of_node);
+	np = of_node_get(dev->of_node);
 	if (!np)
 		return -EINVAL;
 
@@ -1066,7 +1066,7 @@  static int __maybe_unused _get_cpu_power(unsigned long *mW, unsigned long *kHz,
 		return -EINVAL;
 
 	Hz = *kHz * 1000;
-	opp = dev_pm_opp_find_freq_ceil(cpu_dev, &Hz);
+	opp = dev_pm_opp_find_freq_ceil(dev, &Hz);
 	if (IS_ERR(opp))
 		return -EINVAL;
 
@@ -1086,30 +1086,38 @@  static int __maybe_unused _get_cpu_power(unsigned long *mW, unsigned long *kHz,
 
 /**
  * dev_pm_opp_of_register_em() - Attempt to register an Energy Model
- * @cpus	: CPUs for which an Energy Model has to be registered
+ * @dev		: Device for which an Energy Model has to be registered
+ * @cpus	: CPUs for which an Energy Model has to be registered. For
+ *		other type of devices it should be set to NULL.
  *
  * This checks whether the "dynamic-power-coefficient" devicetree property has
  * been specified, and tries to register an Energy Model with it if it has.
+ * Having this property means the voltages are known for OPPs and the EM
+ * might be calculated.
  */
-void dev_pm_opp_of_register_em(struct cpumask *cpus)
+int dev_pm_opp_of_register_em(struct device *dev, 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 em_data_callback em_cb = EM_DATA_CB(_get_power);
 	struct device_node *np;
+	int ret, nr_opp;
 	u32 cap;
 
-	cpu_dev = get_cpu_device(cpu);
-	if (!cpu_dev)
-		return;
+	if (IS_ERR_OR_NULL(dev)) {
+		ret = -EINVAL;
+		goto failed;
+	}
 
-	nr_opp = dev_pm_opp_get_opp_count(cpu_dev);
-	if (nr_opp <= 0)
-		return;
+	nr_opp = dev_pm_opp_get_opp_count(dev);
+	if (nr_opp <= 0) {
+		ret = -EINVAL;
+		goto failed;
+	}
 
-	np = of_node_get(cpu_dev->of_node);
-	if (!np)
-		return;
+	np = of_node_get(dev->of_node);
+	if (!np) {
+		ret = -EINVAL;
+		goto failed;
+	}
 
 	/*
 	 * Register an EM only if the 'dynamic-power-coefficient' property is
@@ -1120,9 +1128,20 @@  void dev_pm_opp_of_register_em(struct cpumask *cpus)
 	 */
 	ret = of_property_read_u32(np, "dynamic-power-coefficient", &cap);
 	of_node_put(np);
-	if (ret || !cap)
-		return;
+	if (ret || !cap) {
+		dev_dbg(dev, "Couldn't find proper 'dynamic-power-coefficient' in DT\n");
+		ret = -EINVAL;
+		goto failed;
+	}
 
-	em_register_perf_domain(cpu_dev, nr_opp, &em_cb, cpus);
+	ret = em_register_perf_domain(dev, nr_opp, &em_cb, cpus);
+	if (ret)
+		goto failed;
+
+	return 0;
+
+failed:
+	dev_dbg(dev, "Couldn't register Energy Model %d\n", ret);
+	return ret;
 }
 EXPORT_SYMBOL_GPL(dev_pm_opp_of_register_em);
diff --git a/include/linux/pm_opp.h b/include/linux/pm_opp.h
index 747861816f4f..822ff9f52bf7 100644
--- a/include/linux/pm_opp.h
+++ b/include/linux/pm_opp.h
@@ -11,6 +11,7 @@ 
 #ifndef __LINUX_OPP_H__
 #define __LINUX_OPP_H__
 
+#include <linux/energy_model.h>
 #include <linux/err.h>
 #include <linux/notifier.h>
 
@@ -360,7 +361,11 @@  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);
+int dev_pm_opp_of_register_em(struct device *dev, struct cpumask *cpus);
+static inline void dev_pm_opp_of_unregister_em(struct device *dev)
+{
+	em_unregister_perf_domain(dev);
+}
 #else
 static inline int dev_pm_opp_of_add_table(struct device *dev)
 {
@@ -400,7 +405,13 @@  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 dev_pm_opp_of_register_em(struct device *dev,
+					    struct cpumask *cpus)
+{
+	return -ENOTSUPP;
+}
+
+static inline void dev_pm_opp_of_unregister_em(struct device *dev)
 {
 }