linux-kernel - Re: [PATCH v4 3/4] scmi-cpufreq: get opp_shared

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Date:   Tue, 8 Dec 2020 12:56:11 +0530
From:   Viresh Kumar <viresh.kumar@...aro.org>
To:     Nicola Mazzucato <nicola.mazzucato@....com>
Cc:     linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-pm@...r.kernel.org, devicetree@...r.kernel.org,
        sudeep.holla@....com, rjw@...ysocki.net, vireshk@...nel.org,
        robh+dt@...nel.org, sboyd@...nel.org, nm@...com,
        daniel.lezcano@...aro.org, morten.rasmussen@....com,
        chris.redpath@....com
Subject: Re: [PATCH v4 3/4] scmi-cpufreq: get opp_shared_cpus from opp-v2 for
 EM

On 08-12-20, 07:22, Nicola Mazzucato wrote:
> On 12/8/20 5:50 AM, Viresh Kumar wrote:
> > On 02-12-20, 17:23, Nicola Mazzucato wrote:
> >>  	nr_opp = dev_pm_opp_get_opp_count(cpu_dev);
> >>  	if (nr_opp <= 0) {
> >> -		dev_dbg(cpu_dev, "OPP table is not ready, deferring probe\n");
> >> -		ret = -EPROBE_DEFER;
> >> -		goto out_free_opp;
> >> +		ret = handle->perf_ops->device_opps_add(handle, cpu_dev);
> >> +		if (ret) {
> >> +			dev_warn(cpu_dev, "failed to add opps to the device\n");
> >> +			goto out_free_cpumask;
> >> +		}
> >> +
> >> +		ret = dev_pm_opp_set_sharing_cpus(cpu_dev, opp_shared_cpus);
> >> +		if (ret) {
> >> +			dev_err(cpu_dev, "%s: failed to mark OPPs as shared: %d\n",
> >> +				__func__, ret);
> >> +			goto out_free_cpumask;
> >> +		}
> >> +
> > 
> > Why do we need to call above two after calling
> > dev_pm_opp_get_opp_count() ?
> 
> Sorry, I am not sure to understand your question here. If there are no opps for
> a device we want to add them to it

Earlier we used to call handle->perf_ops->device_opps_add() and
dev_pm_opp_set_sharing_cpus() before calling dev_pm_opp_get_opp_count(), why is
the order changed now ?

> otherwise no need as they would be duplicated.

I am not sure why they would be duplicated in your case. I though
device_opps_add() is responsible for dynamically adding the OPPs here.

> > And we don't check the return value of
> > the below call anymore, moreover we have to call it twice now.
> 
> This second get_opp_count is required such that we register em with the correct
> opp number after having added them. Without this the opp_count would not be correct.

What if the count is still 0 ? What about deferred probe we were doing earlier ?

-- 
viresh