linux-kernel - Re: [PATCH V3 2/2] cpufreq: scmi: Register for limit change notifications

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Date: Wed, 28 Feb 2024 13:24:53 +0000
From: Lukasz Luba <lukasz.luba@....com>
To: Sibi Sankar <quic_sibis@...cinc.com>
Cc: linux-arm-kernel@...ts.infradead.org, pierre.gondois@....com,
 dietmar.eggemann@....com, morten.rasmussen@....com, viresh.kumar@...aro.org,
 rafael@...nel.org, cristian.marussi@....com, sudeep.holla@....com,
 linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org,
 quic_mdtipton@...cinc.com, linux-arm-msm@...r.kernel.org
Subject: Re: [PATCH V3 2/2] cpufreq: scmi: Register for limit change
 notifications



On 2/27/24 18:16, Sibi Sankar 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>
> ---
> 
> v3:
> * Sanitize range_max received from the notifier. [Pierre]
> * Update commit message.
> 
>   drivers/cpufreq/scmi-cpufreq.c | 29 ++++++++++++++++++++++++++++-
>   1 file changed, 28 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/cpufreq/scmi-cpufreq.c b/drivers/cpufreq/scmi-cpufreq.c
> index 76a0ddbd9d24..78b87b72962d 100644
> --- a/drivers/cpufreq/scmi-cpufreq.c
> +++ b/drivers/cpufreq/scmi-cpufreq.c
> @@ -25,9 +25,13 @@ 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;
>   };
>   
> +const struct scmi_handle *handle;
> +static struct scmi_device *scmi_dev;
>   static struct scmi_protocol_handle *ph;
>   static const struct scmi_perf_proto_ops *perf_ops;
>   static struct cpufreq_driver scmi_cpufreq_driver;
> @@ -151,6 +155,20 @@ 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;
> +
> +	policy->max = clamp(limit_notify->range_max_freq/HZ_PER_KHZ, policy->cpuinfo.min_freq,
> +			    policy->cpuinfo.max_freq);

Please take the division operation out of this clamp() call, somewhere
above. Currently it 'blurs' these stuff, while it's important convertion
to khz. You can call it e.g.:

limit_freq_khz = limit_notify->range_max_freq / HZ_PER_KHZ;

then use in clamp(limit_freq_khz, ...)

> +
> +	cpufreq_update_pressure(policy);
> +
> +	return NOTIFY_OK;
> +}
> +
>   static int scmi_cpufreq_init(struct cpufreq_policy *policy)
>   {
>   	int ret, nr_opp, domain;
> @@ -269,6 +287,15 @@ static int scmi_cpufreq_init(struct cpufreq_policy *policy)
>   		}
>   	}
>   
> +	priv->limit_notify_nb.notifier_call = scmi_limit_notify_cb;
> +	ret = handle->notify_ops->devm_event_notifier_register(scmi_dev, 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;
> @@ -342,8 +369,8 @@ static int scmi_cpufreq_probe(struct scmi_device *sdev)
>   {
>   	int ret;
>   	struct device *dev = &sdev->dev;
> -	const struct scmi_handle *handle;

It should be a compilation error...

>   
> +	scmi_dev = sdev;
>   	handle = sdev->handle;

due to usage here, wasn't it?

>   
>   	if (!handle)