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

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Date: Wed, 28 Feb 2024 22:30:50 +0530
From: Sibi Sankar <quic_sibis@...cinc.com>
To: Lukasz Luba <lukasz.luba@....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 2/28/24 18:54, Lukasz Luba wrote:
> 
> 
> 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.

Lukasz,

Thanks for taking time to review the series!

>>
>> 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, ...)

ack

> 
>> +
>> +    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?

Not really, isn't it getting the first initialization here?
Are there any compiler options that I need to turn on to
catch these?

-Sibi

> 
>>       if (!handle)