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

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Date:   Tue, 8 Dec 2020 10:58:44 +0000
From:   Nicola Mazzucato <nicola.mazzucato@....com>
To:     Viresh Kumar <viresh.kumar@...aro.org>
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 12/8/20 7:26 AM, Viresh Kumar wrote:
> 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 ?

True. The order has changed to take into account the fact that when we have
per-cpu + opp-shared, we don't need to add opps for devices which already have them.

> 
>> 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.

In case of per-cpu + opp-shared, with the "previous order" we would try to add
opps to a device which already has them, in fact attempting to add duplicates.
Nothing wrong with it, but a lot of warnings are thrown.

> 
>>> 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 ?

My assumption is to rely on the two above to fail if there was something wrong.
For the deferred probe, I am not sure it is still a useful case to have, but I
will let Sudeep have his view also on this.

> 

Thanks Viresh, hope it's a bit more clear now.
Nicola