linux-kernel - Re: [PATCH V6 1/1] cpufreq: scmi: Register for limit change notifications

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Message-ID: <CAKfTPtDY965+8wbF-fgFyD4Br-2obQQjJTONwJoPpyYBrdN_VA@mail.gmail.com>
Date: Wed, 30 Oct 2024 15:47:35 +0100
From: Vincent Guittot <vincent.guittot@...aro.org>
To: Sibi Sankar <quic_sibis@...cinc.com>
Cc: sudeep.holla@....com, cristian.marussi@....com, rafael@...nel.org, 
	viresh.kumar@...aro.org, morten.rasmussen@....com, dietmar.eggemann@....com, 
	lukasz.luba@....com, pierre.gondois@....com, 
	linux-arm-kernel@...ts.infradead.org, linux-pm@...r.kernel.org, 
	linux-kernel@...r.kernel.org, quic_mdtipton@...cinc.com, 
	linux-arm-msm@...r.kernel.org
Subject: Re: [PATCH V6 1/1] cpufreq: scmi: Register for limit change notifications

On Wed, 30 Oct 2024 at 14:32, Sibi Sankar <quic_sibis@...cinc.com> wrote:
>
> Register for limit change notifications if supported and use the throttled
> frequency from the notification to apply HW pressure.
>
> Signed-off-by: Sibi Sankar <quic_sibis@...cinc.com>
> Tested-by: Mike Tipton <quic_mdtipton@...cinc.com>
> Reviewed-by: Cristian Marussi <cristian.marussi@....com>
> Reviewed-by: Lukasz Luba <lukasz.luba@....com>
> ---
>
> v6:
> * Unregister the notifier in the exit path to make sure
>   the cpus work across suspend/resume cycles.
>
>  drivers/cpufreq/scmi-cpufreq.c | 38 ++++++++++++++++++++++++++++++++++
>  1 file changed, 38 insertions(+)
>
> diff --git a/drivers/cpufreq/scmi-cpufreq.c b/drivers/cpufreq/scmi-cpufreq.c
> index 5892c73e129d..fb3534eae722 100644
> --- a/drivers/cpufreq/scmi-cpufreq.c
> +++ b/drivers/cpufreq/scmi-cpufreq.c
> @@ -16,6 +16,7 @@
>  #include <linux/export.h>
>  #include <linux/module.h>
>  #include <linux/pm_opp.h>
> +#include <linux/pm_qos.h>
>  #include <linux/slab.h>
>  #include <linux/scmi_protocol.h>
>  #include <linux/types.h>
> @@ -25,7 +26,9 @@ struct scmi_data {
>         int domain_id;
>         int nr_opp;
>         struct device *cpu_dev;
> +       struct cpufreq_policy *policy;
>         cpumask_var_t opp_shared_cpus;
> +       struct notifier_block limit_notify_nb;
>  };
>
>  static struct scmi_protocol_handle *ph;
> @@ -174,6 +177,25 @@ static struct freq_attr *scmi_cpufreq_hw_attr[] = {
>         NULL,
>  };
>
> +static int scmi_limit_notify_cb(struct notifier_block *nb, unsigned long event, void *data)
> +{
> +       struct scmi_data *priv = container_of(nb, struct scmi_data, limit_notify_nb);
> +       struct scmi_perf_limits_report *limit_notify = data;
> +       struct cpufreq_policy *policy = priv->policy;
> +       unsigned int limit_freq_khz;
> +       int ret;
> +
> +       limit_freq_khz = limit_notify->range_max_freq / HZ_PER_KHZ;
> +
> +       policy->max = clamp(limit_freq_khz, policy->cpuinfo.min_freq, policy->cpuinfo.max_freq);
> +
> +       ret = freq_qos_update_request(policy->max_freq_req, policy->max);

If I don't get it wrong, you are using policy->max_freq_req which is
also used by the sysfs scaling_max_freq

This means that your request will be overwritten by the next write
into scaling_max_freq and/or you will overwrite a constraint set by
userspace.

You have to create your own freq_qos_request and add it to the list of
cpufreq qos request



> +       if (ret < 0)
> +               pr_warn("failed to update freq constraint: %d\n", ret);
> +
> +       return NOTIFY_OK;
> +}
> +
>  static int scmi_cpufreq_init(struct cpufreq_policy *policy)
>  {
>         int ret, nr_opp, domain;
> @@ -181,6 +203,7 @@ static int scmi_cpufreq_init(struct cpufreq_policy *policy)
>         struct device *cpu_dev;
>         struct scmi_data *priv;
>         struct cpufreq_frequency_table *freq_table;
> +       struct scmi_device *sdev = cpufreq_get_driver_data();
>
>         cpu_dev = get_cpu_device(policy->cpu);
>         if (!cpu_dev) {
> @@ -294,6 +317,17 @@ static int scmi_cpufreq_init(struct cpufreq_policy *policy)
>                 }
>         }
>
> +       priv->limit_notify_nb.notifier_call = scmi_limit_notify_cb;
> +       ret = sdev->handle->notify_ops->devm_event_notifier_register(sdev, SCMI_PROTOCOL_PERF,
> +                                                       SCMI_EVENT_PERFORMANCE_LIMITS_CHANGED,
> +                                                       &domain,
> +                                                       &priv->limit_notify_nb);
> +       if (ret)
> +               dev_warn(&sdev->dev,
> +                        "failed to register for limits change notifier for domain %d\n", domain);
> +
> +       priv->policy = policy;
> +
>         return 0;
>
>  out_free_opp:
> @@ -310,8 +344,10 @@ static int scmi_cpufreq_init(struct cpufreq_policy *policy)
>
>  static void scmi_cpufreq_exit(struct cpufreq_policy *policy)
>  {
> +       struct scmi_device *sdev = cpufreq_get_driver_data();
>         struct scmi_data *priv = policy->driver_data;
>
> +       sdev->handle->notify_ops->devm_event_notifier_unregister(sdev, &priv->limit_notify_nb);
>         dev_pm_opp_free_cpufreq_table(priv->cpu_dev, &policy->freq_table);
>         dev_pm_opp_remove_all_dynamic(priv->cpu_dev);
>         free_cpumask_var(priv->opp_shared_cpus);
> @@ -370,6 +406,8 @@ static int scmi_cpufreq_probe(struct scmi_device *sdev)
>         if (!handle)
>                 return -ENODEV;
>
> +       scmi_cpufreq_driver.driver_data = sdev;
> +
>         perf_ops = handle->devm_protocol_get(sdev, SCMI_PROTOCOL_PERF, &ph);
>         if (IS_ERR(perf_ops))
>                 return PTR_ERR(perf_ops);
> --
> 2.34.1
>