Re: [PATCH 1/4] PM / EM: and devices to Energy Model

[Lukasz Luba]

On 1/20/20 6:27 PM, Dietmar Eggemann wrote:
> On 20/01/2020 16:09, Quentin Perret wrote:
> > Hey Lukasz,
> >
> > On Monday 20 Jan 2020 at 14:52:07 (+0000), Lukasz Luba wrote:
> > > On 1/17/20 10:54 AM, Quentin Perret wrote:
> > > > Suggested alternative: have two registration functions like so:
> > > >
> > > > 	int em_register_dev_pd(struct device *dev, unsigned int nr_states,
> > > > 			       struct em_data_callback *cb);
> > > > 	int em_register_cpu_pd(cpumask_t *span, unsigned int nr_states,
> > > > 			       struct em_data_callback *cb);
> > >
> > > Interesting, in the internal review Dietmar asked me to remove these two
> > > functions. I had the same idea, which would simplify a bit the
> > > registration and it does not need to check the dev->bus if it is CPU.
> > >
> > > Unfortunately, we would need also two function in drivers/opp/of.c:
> > > dev_pm_opp_of_register_cpu_em(policy->cpus);
> > > and
> > > dev_pm_opp_of_register_dev_em(dev);
> > >
> > > Thus, I have created only one registration function, which you can see
> > > in this patch set.
> >
> > Right, I can see how having a unified API would be appealing, but the
> > OPP dependency is a nono, so we'll need to work around one way or
> > another.
> >
> > FWIW, I don't think having separate APIs for CPUs and other devices is
> > that bad given that we already have entirely different frameworks to
> > drive their respective frequencies. And the _cpu variants are basically
> > just wrappers around the _dev ones, so not too bad either IMO :).
>
> It's true that we need the policy->cpus cpumask only for cpu devices and
> we have it available when we call em_register_perf_domain()
> [scmi-cpufreq.c driver] or the OPP wrapper dev_pm_opp_of_register_em()
> [e.g. cpufreq-dt.c driver].
>
> And we shouldn't make EM code dependent on OPP.
>
> But can't we add 'struct cpumask *mask' as an additional argument to
> both which can be set to NULL for (devfreq) devices?
>
> We can check in em_register_perf_domain() that we got a valid cpumask
> for a cpu device and ignore it for (devfreq) devices.

I think we could avoid this additional argument 'cpumask'. I have
checked the cpufreq_cpu_get function, which should do be good for this:

---------->8-------------------------
static int _get_sharing_cpus(struct device *cpu_dev, struct cpumask *span)
{
        struct cpufreq_policy *policy;

        policy = cpufreq_cpu_get(cpu_dev->id);
        if (policy) {
                cpumask_copy(span, policy->cpus);
                cpufreq_cpu_put(policy);
                return 0;
        } else {
                return -EINVAL;
        }
}
--------------------------8<-------------------------------

It would be a replacement for:
ret = dev_pm_opp_get_sharing_cpus(dev, span);

Regards,
Lukasz