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

[Cristian Marussi <cristian.marussi@arm.com>]

On Thu, Mar 28, 2024 at 01:11:31PM +0530, Sibi Sankar wrote:
> Register for limit change notifications if supported and use the throttled
> frequency from the notification to apply HW pressure.
> 

Hi Sibi,

a bit late on this, sorry.

Just a couple of nitpicks down below.

> Signed-off-by: Sibi Sankar <quic_sibis@quicinc.com>
> ---
> 
> 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);
> +
> +	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,

or &data->sdev->dev which refers to this driver ? which is more informational ? no strong opinion just a question...

> +			 "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;

	^^^ ... you dont need to pass around handle AND sdev really
                since you can access the handle from sdev.

> +	scmi_cpufreq_driver.driver_data = data;

This is slightly better, but, as said, does not solve the multi-instance issue...
...the scmi cpufreq driver remains a driver that works only if instantiated (probed)
once, given how the CPUFreq core handles cpufreq_driver registration itself...

...just a note about something to work on in the future...NOT a concern for this series.

In general,

LGTM.

Thanks,
Cristian