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

[Sibi Sankar <quic_sibis@xxxxxxxxxxx>]

On 1/29/24 21:29, Cristian Marussi wrote:
> On Wed, Jan 17, 2024 at 04:11:16PM +0530, 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.

Christian,

Thanks for taking time to review the series.

> > Signed-off-by: Sibi Sankar <quic_sibis@xxxxxxxxxxx>
> > ---
> >
> > 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;
> > +	cpufreq_update_pressure(policy);
> > +
> > +	return NOTIFY_OK;
> > +}
> > +
> >   static int scmi_cpufreq_init(struct cpufreq_policy *policy)
> >   {
> >   	int ret, nr_opp, domain;
> > @@ -151,6 +171,7 @@ 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_perf_notify_info info = {};
> >   
> >   	cpu_dev = get_cpu_device(policy->cpu);
> >   	if (!cpu_dev) {
> > @@ -250,6 +271,25 @@ static int scmi_cpufreq_init(struct cpufreq_policy *policy)
> >   	policy->fast_switch_possible =
> >   		perf_ops->fast_switch_possible(ph, domain);
> >   
> > +	ret = perf_ops->perf_notify_support(ph, domain, &info);
> > +	if (ret)
> > +		dev_warn(cpu_dev, "failed to get supported notifications: %d\n", ret);
> > +
> > +	if (info.perf_limit_notify) {
> > +		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_err(cpu_dev, "Error in registering limit change notifier for domain %d\n",
> > +				domain);
> > +			return ret;
> > +		}
>
> Is there a reason to fail completely here if it was not possible to register
> the notifier ? (even though expected to succeed given perf_limit_notify
> was true...)
>
> Maybe a big fat warn that the system perf could be degraded, but
> carrying on ?
>
> Or maybe you have in mind a good reason to fail like you did, so please
> explain in that case in a comment.

ack a warn should suffice here

-Sibi

> Thanks,
> Cristian