Re: [Patch v3 3/6] cpufreq: qcom-cpufreq-hw: Add dcvs interrupt support

[Thara Gopinath]

On 7/9/21 2:46 AM, Viresh Kumar wrote:
> On 08-07-21, 08:06, Thara Gopinath wrote:
> >   static int qcom_cpufreq_hw_cpu_init(struct cpufreq_policy *policy)
> >   {
> >   	struct platform_device *pdev = cpufreq_get_driver_data();
> > @@ -370,6 +480,10 @@ static int qcom_cpufreq_hw_cpu_init(struct cpufreq_policy *policy)
> >   			dev_warn(cpu_dev, "failed to enable boost: %d\n", ret);
> >   	}
> >   
> > +	ret = qcom_cpufreq_hw_lmh_init(policy, index);
>
> You missed unregistering EM here (which is also missing from exit,
> which you need to fix first in a separate patch).

Hi!

So how exactly do you do this? I checked other users of the api and I do 
not see any free. I would say if needed, it should be a separate patch 
and outside of this series.

> > +	if (ret)
> > +		goto error;
> > +
> >   	return 0;
> >   error:
> >   	kfree(data);
> > @@ -389,6 +503,10 @@ static int qcom_cpufreq_hw_cpu_exit(struct cpufreq_policy *policy)
> >   
> >   	dev_pm_opp_remove_all_dynamic(cpu_dev);
> >   	dev_pm_opp_of_cpumask_remove_table(policy->related_cpus);
> > +	if (data->lmh_dcvs_irq > 0) {
> > +		devm_free_irq(cpu_dev, data->lmh_dcvs_irq, data);
>
> Why using devm variants here and while requesting the irq ?
>
> > +		cancel_delayed_work_sync(&data->lmh_dcvs_poll_work);
> > +	}
>
> Please move this to qcom_cpufreq_hw_lmh_exit() or something.

Ok.

> Now with sequence of disabling interrupt, etc, I see a potential
> problem.
>
> CPU0                                    CPU1
>
> qcom_cpufreq_hw_cpu_exit()
> -> devm_free_irq();
>                                          qcom_lmh_dcvs_poll()
>                                          -> qcom_lmh_dcvs_notify()
>                                            -> enable_irq()
>
> -> cancel_delayed_work_sync();
>
>
> What will happen if enable_irq() gets called after freeing the irq ?
> Not sure, but it looks like you will hit this then from manage.c:
>
> WARN(!desc->irq_data.chip, KERN_ERR "enable_irq before
>                                       setup/request_irq: irq %u\n", irq))
>
> ?
>
> You got a chicken n egg problem :)

Yes indeed! But also it is a very rare chicken and egg problem.
The scenario here is that the cpus are busy and running load causing a 
thermal overrun and lmh is engaged. At the same time for this issue to 
be hit the cpu is trying to exit/disable cpufreq. Calling 
cancel_delayed_work_sync first could solve this issue, right ? 
cancel_delayed_work_sync guarantees the work not to be pending even if
it requeues itself on return. So once the delayed work is cancelled, the 
interrupts can be safely disabled. Thoughts ?


>

--
Warm Regards
Thara (She/Her/Hers)