linux-kernel - Re: [PATCH V2 4/5] cpufreq: Register notifiers with the PM QoS framework

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Message-ID: <20190222114446.cmwoe7tanxvf2gxh@e107158-lin.cambridge.arm.com>
Date:   Fri, 22 Feb 2019 11:44:46 +0000
From:   Qais Yousef <qais.yousef@....com>
To:     Viresh Kumar <viresh.kumar@...aro.org>
Cc:     Rafael Wysocki <rjw@...ysocki.net>, linux-pm@...r.kernel.org,
        Vincent Guittot <vincent.guittot@...aro.org>, mka@...omium.org,
        juri.lelli@...il.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH V2 4/5] cpufreq: Register notifiers with the PM QoS
 framework

Hi Verish

On 02/21/19 16:59, Viresh Kumar wrote:

[...]

> @@ -2239,6 +2314,8 @@ static int cpufreq_set_policy(struct cpufreq_policy *policy,
>  			      struct cpufreq_policy *new_policy)
>  {
>  	struct cpufreq_governor *old_gov;
> +	struct device *cpu_dev = get_cpu_device(policy->cpu);
> +	unsigned long min, max;
>  	int ret;
>  
>  	pr_debug("setting new policy for CPU %u: %u - %u kHz\n",
> @@ -2253,11 +2330,23 @@ static int cpufreq_set_policy(struct cpufreq_policy *policy,
>  	if (new_policy->min > new_policy->max)
>  		return -EINVAL;
>  
> +	min = dev_pm_qos_read_value(cpu_dev, DEV_PM_QOS_MIN_FREQUENCY);
> +	max = dev_pm_qos_read_value(cpu_dev, DEV_PM_QOS_MAX_FREQUENCY);
> +
> +	if (min > new_policy->min)
> +		new_policy->min = min;
> +	if (max < new_policy->max)
> +		new_policy->max = max;
> +

Assuming for example min and max range from 1-10, and thermal throttles max to
5 using pm_qos to deal with temporary thermal pressure. But shortly after
a driver thinks that max shouldn't be greater than 7 for one reason or another.

What will happen after thermal pressure removes its constraint? Will we still
remember the driver's request and apply it so max is set to 7 instead of 10?

Thanks

--
Qais Yousef