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

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Date:   Fri, 9 Jul 2021 12:16:46 +0530
From:   Viresh Kumar <viresh.kumar@...aro.org>
To:     Thara Gopinath <thara.gopinath@...aro.org>
Cc:     agross@...nel.org, bjorn.andersson@...aro.org, rui.zhang@...el.com,
        daniel.lezcano@...aro.org, rjw@...ysocki.net, robh+dt@...nel.org,
        tdas@...eaurora.org, mka@...omium.org,
        linux-arm-msm@...r.kernel.org, linux-pm@...r.kernel.org,
        linux-kernel@...r.kernel.org, devicetree@...r.kernel.org
Subject: Re: [Patch v3 3/6] cpufreq: qcom-cpufreq-hw: Add dcvs interrupt
 support

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).

> +	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.

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 :)

-- 
viresh