linux-kernel - Re: [PATCH RFC 2/4] OPP: Add and export helper to set bandwidth

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Message-ID: <20190711174043.GU7234@tuxbook-pro>
Date:   Thu, 11 Jul 2019 10:40:43 -0700
From:   Bjorn Andersson <bjorn.andersson@...aro.org>
To:     Sibi Sankar <sibis@...eaurora.org>
Cc:     viresh.kumar@...aro.org, nm@...com, sboyd@...nel.org,
        georgi.djakov@...aro.org, agross@...nel.org,
        david.brown@...aro.org, robh+dt@...nel.org, mark.rutland@....com,
        rjw@...ysocki.net, linux-arm-msm@...r.kernel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-pm@...r.kernel.org, saravanak@...gle.com
Subject: Re: [PATCH RFC 2/4] OPP: Add and export helper to set bandwidth

On Thu 27 Jun 06:34 PDT 2019, Sibi Sankar wrote:

> Add and export 'dev_pm_opp_set_bw' to set the bandwidth
> levels associated with an OPP for a given frequency.
> 

While this looks quite reasonable I'm uncertain about the overall OPP
API.

With the profiling based (bwmon/llcc) approach we would acquire the peak
bandwidth from the OPP table and calculate the average dynamically,
based on measurements and heuristics.

For that I think we will have a struct dev_pm_opp at hand (e.g. from
devfreq_recommended_opp() or similar), from which we want to read the
peak value and then apply the icc vote. Or would we want to update the
avg bw and then apply the opp using a method like this? (In which case
we probably don't want to pass a freq, but a struct dev_pm_opp *, to
avoid the additional lookup)

Regards,
Bjorn

> Signed-off-by: Sibi Sankar <sibis@...eaurora.org>
> ---
>  drivers/opp/core.c     | 46 ++++++++++++++++++++++++++++++++++++++++++
>  include/linux/pm_opp.h |  6 ++++++
>  2 files changed, 52 insertions(+)
> 
> diff --git a/drivers/opp/core.c b/drivers/opp/core.c
> index c85c04dc2c7de..78f42960860d1 100644
> --- a/drivers/opp/core.c
> +++ b/drivers/opp/core.c
> @@ -746,6 +746,52 @@ static int _set_required_opps(struct device *dev,
>  	return ret;
>  }
>  
> +/**
> + * dev_pm_opp_set_bw() - Configures OPP bandwidth levels
> + * @dev:	device for which we do this operation
> + * @freq:	bandwidth values to set with matching 'freq'
> + *
> + * This configures the bandwidth to the levels specified
> + * by the OPP corresponding to the given frequency.
> + *
> + * Return: 0 on success or a negative error value.
> + */
> +int dev_pm_opp_set_bw(struct device *dev, unsigned long freq)
> +{
> +	struct opp_table *opp_table;
> +	struct dev_pm_opp *opp;
> +	int ret = 0;
> +	int i;
> +
> +	opp = dev_pm_opp_find_freq_exact(dev, freq, true);
> +	if (IS_ERR(opp))
> +		return PTR_ERR(opp);
> +
> +	opp_table = _find_opp_table(dev);
> +	if (IS_ERR(opp_table)) {
> +		dev_err(dev, "%s: device opp table doesn't exist\n", __func__);
> +		ret = PTR_ERR(opp_table);
> +		goto put_opp;
> +	}
> +
> +	if (IS_ERR_OR_NULL(opp_table->paths)) {
> +		ret = -ENODEV;
> +		goto put_opp_table;
> +	}
> +
> +	for (i = 0; i < opp_table->path_count; i++) {
> +		ret = icc_set_bw(opp_table->paths[i], opp->bandwidth[i].avg,
> +				 opp->bandwidth[i].peak);
> +	}
> +
> +put_opp_table:
> +	dev_pm_opp_put_opp_table(opp_table);
> +put_opp:
> +	dev_pm_opp_put(opp);
> +	return ret;
> +}
> +EXPORT_SYMBOL_GPL(dev_pm_opp_set_bw);
> +
>  /**
>   * dev_pm_opp_set_rate() - Configure new OPP based on frequency
>   * @dev:	 device for which we do this operation
> diff --git a/include/linux/pm_opp.h b/include/linux/pm_opp.h
> index a17c462974851..1cdc2d0a2b20e 100644
> --- a/include/linux/pm_opp.h
> +++ b/include/linux/pm_opp.h
> @@ -152,6 +152,7 @@ struct opp_table *dev_pm_opp_attach_genpd(struct device *dev, const char **names
>  void dev_pm_opp_detach_genpd(struct opp_table *opp_table);
>  int dev_pm_opp_xlate_performance_state(struct opp_table *src_table, struct opp_table *dst_table, unsigned int pstate);
>  int dev_pm_opp_set_rate(struct device *dev, unsigned long target_freq);
> +int dev_pm_opp_set_bw(struct device *dev, unsigned long freq);
>  int dev_pm_opp_set_sharing_cpus(struct device *cpu_dev, const struct cpumask *cpumask);
>  int dev_pm_opp_get_sharing_cpus(struct device *cpu_dev, struct cpumask *cpumask);
>  void dev_pm_opp_remove_table(struct device *dev);
> @@ -336,6 +337,11 @@ static inline int dev_pm_opp_set_rate(struct device *dev, unsigned long target_f
>  	return -ENOTSUPP;
>  }
>  
> +static inline int dev_pm_opp_set_bw(struct device *dev, unsigned long freq)
> +{
> +	return -ENOTSUPP;
> +}
> +
>  static inline int dev_pm_opp_set_sharing_cpus(struct device *cpu_dev, const struct cpumask *cpumask)
>  {
>  	return -ENOTSUPP;
> -- 
> The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum,
> a Linux Foundation Collaborative Project
>