linux-kernel - Re: [PATCH V2 4/4] cpufreq: scmi: Register for limit change notifications

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Message-ID: <145277d6-ddb5-6dd6-c534-d92ea2d1ff28@quicinc.com>
Date: Tue, 13 Feb 2024 11:16:03 +0530
From: Sibi Sankar <quic_sibis@...cinc.com>
To: Pierre Gondois <pierre.gondois@....com>
CC: <linux-arm-kernel@...ts.infradead.org>, <sudeep.holla@....com>,
        <linux-pm@...r.kernel.org>, <cristian.marussi@....com>,
        <linux-kernel@...r.kernel.org>, <rafael@...nel.org>,
        <viresh.kumar@...aro.org>, <quic_mdtipton@...cinc.com>,
        <lukasz.luba@....com>, <linux-arm-msm@...r.kernel.org>,
        <dietmar.eggemann@....com>, <morten.rasmussen@....com>
Subject: Re: [PATCH V2 4/4] cpufreq: scmi: Register for limit change
 notifications



On 1/31/24 19:59, Pierre Gondois wrote:
> Hello Sibi,
> 
> On 1/17/24 11:41, Sibi Sankar wrote:
>> Register for limit change notifications if supported with the help of
>> perf_notify_support interface and determine the throttled frequency
>> using the perf_freq_xlate to apply HW pressure.
>>

Hey Pierre,

Thanks for taking time to review the series.

>> Signed-off-by: Sibi Sankar <quic_sibis@...cinc.com>
>> ---
>>
>> v2:
>> * Export cpufreq_update_pressure and use it directly [Lukasz]
>>
>>   drivers/cpufreq/scmi-cpufreq.c | 42 +++++++++++++++++++++++++++++++++-
>>   1 file changed, 41 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/cpufreq/scmi-cpufreq.c 
>> b/drivers/cpufreq/scmi-cpufreq.c
>> index 4ee23f4ebf4a..e0aa85764451 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;
>> @@ -144,6 +148,22 @@ scmi_get_cpu_power(struct device *cpu_dev, 
>> unsigned long *power,
>>       return 0;
>>   }
>> +static int scmi_limit_notify_cb(struct notifier_block *nb, unsigned 
>> long event, void *data)
>> +{
>> +    unsigned long freq_hz;
>> +    struct scmi_perf_limits_report *limit_notify = data;
>> +    struct scmi_data *priv = container_of(nb, struct scmi_data, 
>> limit_notify_nb);
>> +    struct cpufreq_policy *policy = priv->policy;
>> +
>> +    if (perf_ops->perf_freq_xlate(ph, priv->domain_id, 
>> limit_notify->range_max, &freq_hz))
>> +        return NOTIFY_OK;
>> +
>> +    policy->max = freq_hz / HZ_PER_KHZ;
> 
> Maybe 'policy->max' should be checked. The limits received by SCMI is 
> blindly
> trusted. This might be ok, but could also lead to some inconsistency.
> 
> The scmi_cpufreq_driver's verify() callback could be used.

ack, will fix this in the next re-spin.

> 
> ---
> 
> I think there might also be corner cases where the SCP might advertise
> the maximum boosted frequency as the max limit, but boosting might not
> be enabled on the kernel side.
> So I think this should be checked when setting 'policy->max',

ack

-Sibi
> 
> Regards,
> Pierre
> 
[...]
>>       if (!handle)