linux-kernel - Re: [PATCH 1/2] PM: EM: Add min/max available performance state limits

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Message-ID: <08bff6ab-dcdc-42b6-b8ad-5938f0119385@arm.com>
Date: Tue, 9 Apr 2024 15:47:56 +0100
From: Hongyan Xia <hongyan.xia2@....com>
To: Lukasz Luba <lukasz.luba@....com>, linux-kernel@...r.kernel.org,
 linux-pm@...r.kernel.org
Cc: dietmar.eggemann@....com, linux-arm-kernel@...ts.infradead.org,
 sudeep.holla@....com, cristian.marussi@....com,
 linux-samsung-soc@...r.kernel.org, rafael@...nel.org,
 viresh.kumar@...aro.org, quic_sibis@...cinc.com
Subject: Re: [PATCH 1/2] PM: EM: Add min/max available performance state
 limits

On 03/04/2024 17:23, Lukasz Luba wrote:
> [...]
>
> diff --git a/kernel/power/energy_model.c b/kernel/power/energy_model.c
> index 927cc55ba0b3d..1a8b394251cb2 100644
> --- a/kernel/power/energy_model.c
> +++ b/kernel/power/energy_model.c
> @@ -628,6 +628,8 @@ int em_dev_register_perf_domain(struct device *dev, unsigned int nr_states,
>   		goto unlock;
>   
>   	dev->em_pd->flags |= flags;
> +	dev->em_pd->min_ps = 0;
> +	dev->em_pd->max_ps = nr_states - 1;
>   
>   	em_cpufreq_update_efficiencies(dev, dev->em_pd->em_table->state);
>   
> @@ -856,3 +858,49 @@ int em_dev_update_chip_binning(struct device *dev)
>   	return em_recalc_and_update(dev, pd, em_table);
>   }
>   EXPORT_SYMBOL_GPL(em_dev_update_chip_binning);
> +
> +
> +/**
> + * em_update_performance_limits() - Update Energy Model with performance
> + *				limits information.
> + * @pd			: Performance Domain with EM that has to be updated.
> + * @freq_min_khz	: New minimum allowed frequency for this device.
> + * @freq_max_khz	: New maximum allowed frequency for this device.
> + *
> + * This function allows to update the EM with information about available
> + * performance levels. It takes the minimum and maximum frequency in kHz
> + * and does internal translation to performance levels.
> + * Returns 0 on success or -EINVAL when failed.
> + */
> +int em_update_performance_limits(struct em_perf_domain *pd,
> +		unsigned long freq_min_khz, unsigned long freq_max_khz)
> +{
> +	struct em_perf_state *table;
> +	int min_ps = -1;
> +	int max_ps = -1;
> +	int i;
> +
> +	if (!pd)
> +		return -EINVAL;
> +
> +	rcu_read_lock();
> +	table = em_perf_state_from_pd(pd);
> +
> +	for (i = 0; i < pd->nr_perf_states; i++) {
> +		if (freq_min_khz == table[i].frequency)
> +			min_ps = i;
> +		if (freq_max_khz == table[i].frequency)
> +			max_ps = i;
> +	}
> +	rcu_read_unlock();
> +
> +	/* Only update when both are found and sane */
> +	if (min_ps < 0 || max_ps < 0 || max_ps < min_ps)
> +		return -EINVAL;
> +
> +	pd->min_ps = min_ps;
> +	pd->max_ps = max_ps;

Are we sure we are protected against multiple simultaneous updates? Or 
is this a concern for the caller?

The rest of the patch LGTM.

> +
> +	return 0;
> +}
> +EXPORT_SYMBOL_GPL(em_update_performance_limits);