Re: [PATCH V4 2/2] cpufreq: scmi: Register for limit change notifications

[Vincent Guittot]

Hi Sibi,

On Thu, 28 Mar 2024 at 08:42, Sibi Sankar <quic_sibis@xxxxxxxxxxx> 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@xxxxxxxxxxx>
> ---
>
> v4:
> * Use a interim variable to show the khz calc. [Lukasz]
> * Use driver_data to pass on the handle and scmi_dev instead of using
>   global variables. Dropped Lukasz's Rb due to adding these minor
>   changes.
>
>  drivers/cpufreq/scmi-cpufreq.c | 44 ++++++++++++++++++++++++++++++++++
>  1 file changed, 44 insertions(+)
>
> diff --git a/drivers/cpufreq/scmi-cpufreq.c b/drivers/cpufreq/scmi-cpufreq.c
> index 3b4f6bfb2f4c..d946b7a08258 100644
> --- a/drivers/cpufreq/scmi-cpufreq.c
> +++ b/drivers/cpufreq/scmi-cpufreq.c
> @@ -21,11 +21,18 @@
>  #include <linux/types.h>
>  #include <linux/units.h>
>
> +struct scmi_cpufreq_driver_data {
> +       struct scmi_device *sdev;
> +       const struct scmi_handle *handle;
> +};
> +
>  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 +181,22 @@ 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;
> +
> +       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);
> +
> +       cpufreq_update_pressure(policy);

I noticed your patch while looking for other things in the archive but
I don't think this is the right way to do it.

cpufreq_update_pressure() aims to set to the scheduler the aggregation
of all cappings set to cpufreq through the pm_qos and
freq_qos_add_request(). Calling this function directly in scmi
notification callback will overwrite the pm_qos aggregation. And at
the opposite, any update of a pm_qos constraint will overwrite scmi
notification. Instead you should better set a pm_qos constraint like
others

> +
> +       return NOTIFY_OK;
> +}
> +
>  static int scmi_cpufreq_init(struct cpufreq_policy *policy)
>  {
>         int ret, nr_opp, domain;
> @@ -181,6 +204,7 @@ 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_cpufreq_driver_data *data = cpufreq_get_driver_data();
>
>         cpu_dev = get_cpu_device(policy->cpu);
>         if (!cpu_dev) {
> @@ -294,6 +318,17 @@ static int scmi_cpufreq_init(struct cpufreq_policy *policy)
>                 }
>         }
>
> +       priv->limit_notify_nb.notifier_call = scmi_limit_notify_cb;
> +       ret = data->handle->notify_ops->devm_event_notifier_register(data->sdev, SCMI_PROTOCOL_PERF,
> +                                                       SCMI_EVENT_PERFORMANCE_LIMITS_CHANGED,
> +                                                       &domain,
> +                                                       &priv->limit_notify_nb);
> +       if (ret)
> +               dev_warn(cpu_dev,
> +                        "failed to register for limits change notifier for domain %d\n", domain);
> +
> +       priv->policy = policy;
> +
>         return 0;
>
>  out_free_opp:
> @@ -366,12 +401,21 @@ static int scmi_cpufreq_probe(struct scmi_device *sdev)
>         int ret;
>         struct device *dev = &sdev->dev;
>         const struct scmi_handle *handle;
> +       struct scmi_cpufreq_driver_data *data;
>
>         handle = sdev->handle;
>
>         if (!handle)
>                 return -ENODEV;
>
> +       data = devm_kzalloc(dev, sizeof(*data), GFP_KERNEL);
> +       if (!data)
> +               return -ENOMEM;
> +
> +       data->sdev = sdev;
> +       data->handle = handle;
> +       scmi_cpufreq_driver.driver_data = data;
> +
>         perf_ops = handle->devm_protocol_get(sdev, SCMI_PROTOCOL_PERF, &ph);
>         if (IS_ERR(perf_ops))
>                 return PTR_ERR(perf_ops);
> --
> 2.34.1
>
>