Re: [v4, 6/8] PM / OPP: Support adjusting OPP voltages at runtime

[Matthias Brugger]

On 13/08/2019 15:31, Andrew-sh.Cheng wrote:
> From: Stephen Boyd <sboyd@xxxxxxxxxxxxxx>
> 
> On some SoCs the Adaptive Voltage Scaling (AVS) technique is
> employed to optimize the operating voltage of a device. At a
> given frequency, the hardware monitors dynamic factors and either
> makes a suggestion for how much to adjust a voltage for the
> current frequency, or it automatically adjusts the voltage
> without software intervention. Add an API to the OPP library for
> the former case, so that AVS type devices can update the voltages
> for an OPP when the hardware determines the voltage should
> change. The assumption is that drivers like CPUfreq or devfreq
> will register for the OPP notifiers and adjust the voltage
> according to suggestions that AVS makes.
> 
> This patch is devired from [1] submitted by Stephen.
> [1] https://lore.kernel.org/patchwork/patch/599279/
> 
> Signed-off-by: Stephen Boyd <sboyd@xxxxxxxxxxxxxx>
> Signed-off-by: Roger Lu <roger.lu@xxxxxxxxxxxx>

Nit: your signed-off-by tag is missing.

Regards,
Matthias

> ---
>  drivers/opp/core.c     | 63 ++++++++++++++++++++++++++++++++++++++++++++++++++
>  include/linux/pm_opp.h | 11 +++++++++
>  2 files changed, 74 insertions(+)
> 
> diff --git a/drivers/opp/core.c b/drivers/opp/core.c
> index c094d5d20fd7..407a07f29b12 100644
> --- a/drivers/opp/core.c
> +++ b/drivers/opp/core.c
> @@ -2054,6 +2054,69 @@ static int _opp_set_availability(struct device *dev, unsigned long freq,
>  }
>  
>  /**
> + * dev_pm_opp_adjust_voltage() - helper to change the voltage of an OPP
> + * @dev:		device for which we do this operation
> + * @freq:		OPP frequency to adjust voltage of
> + * @u_volt:		new OPP voltage
> + *
> + * Return: -EINVAL for bad pointers, -ENOMEM if no memory available for the
> + * copy operation, returns 0 if no modifcation was done OR modification was
> + * successful.
> + */
> +int dev_pm_opp_adjust_voltage(struct device *dev, unsigned long freq,
> +			      unsigned long u_volt)
> +{
> +	struct opp_table *opp_table;
> +	struct dev_pm_opp *tmp_opp, *opp = ERR_PTR(-ENODEV);
> +	int r = 0;
> +
> +	/* Find the opp_table */
> +	opp_table = _find_opp_table(dev);
> +	if (IS_ERR(opp_table)) {
> +		r = PTR_ERR(opp_table);
> +		dev_warn(dev, "%s: Device OPP not found (%d)\n", __func__, r);
> +		return r;
> +	}
> +
> +	mutex_lock(&opp_table->lock);
> +
> +	/* Do we have the frequency? */
> +	list_for_each_entry(tmp_opp, &opp_table->opp_list, node) {
> +		if (tmp_opp->rate == freq) {
> +			opp = tmp_opp;
> +			break;
> +		}
> +	}
> +
> +	if (IS_ERR(opp)) {
> +		r = PTR_ERR(opp);
> +		goto adjust_unlock;
> +	}
> +
> +	/* Is update really needed? */
> +	if (opp->supplies->u_volt == u_volt)
> +		goto adjust_unlock;
> +
> +	opp->supplies->u_volt = u_volt;
> +
> +	dev_pm_opp_get(opp);
> +	mutex_unlock(&opp_table->lock);
> +
> +	/* Notify the voltage change of the OPP */
> +	blocking_notifier_call_chain(&opp_table->head, OPP_EVENT_ADJUST_VOLTAGE,
> +				     opp);
> +
> +	dev_pm_opp_put(opp);
> +	goto adjust_put_table;
> +
> +adjust_unlock:
> +	mutex_unlock(&opp_table->lock);
> +adjust_put_table:
> +	dev_pm_opp_put_opp_table(opp_table);
> +	return r;
> +}
> +
> +/**
>   * dev_pm_opp_enable() - Enable a specific OPP
>   * @dev:	device for which we do this operation
>   * @freq:	OPP frequency to enable
> diff --git a/include/linux/pm_opp.h b/include/linux/pm_opp.h
> index af5021f27cb7..86947d53e8c4 100644
> --- a/include/linux/pm_opp.h
> +++ b/include/linux/pm_opp.h
> @@ -22,6 +22,7 @@ struct opp_table;
>  
>  enum dev_pm_opp_event {
>  	OPP_EVENT_ADD, OPP_EVENT_REMOVE, OPP_EVENT_ENABLE, OPP_EVENT_DISABLE,
> +	OPP_EVENT_ADJUST_VOLTAGE,
>  };
>  
>  /**
> @@ -111,6 +112,9 @@ int dev_pm_opp_add(struct device *dev, unsigned long freq,
>  void dev_pm_opp_remove(struct device *dev, unsigned long freq);
>  void dev_pm_opp_remove_all_dynamic(struct device *dev);
>  
> +int dev_pm_opp_adjust_voltage(struct device *dev, unsigned long freq,
> +			      unsigned long u_volt);
> +
>  int dev_pm_opp_enable(struct device *dev, unsigned long freq);
>  
>  int dev_pm_opp_disable(struct device *dev, unsigned long freq);
> @@ -234,6 +238,13 @@ static inline void dev_pm_opp_remove_all_dynamic(struct device *dev)
>  {
>  }
>  
> +static inline int
> +dev_pm_opp_adjust_voltage(struct device *dev, unsigned long freq,
> +			  unsigned long u_volt)
> +{
> +	return 0;
> +}
> +
>  static inline int dev_pm_opp_enable(struct device *dev, unsigned long freq)
>  {
>  	return 0;
>