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

[Sibi Sankar]

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@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;
>
> 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)