linux-kernel - Re: [PATCH v6 04/10] PM / EM: add support for other devices than CPUs in Energy Model

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Date:   Fri, 10 Apr 2020 13:12:28 +0200
From:   Luis Gerhorst <linux-kernel@...sgerhorst.de>
To:     Lukasz Luba <lukasz.luba@....com>
Cc:     linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        dri-devel@...ts.freedesktop.org, linux-omap@...r.kernel.org,
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Subject: Re: [PATCH v6 04/10] PM / EM: add support for other devices than CPUs in Energy Model


Lukasz Luba writes:

> +/**
> + * em_dev_unregister_perf_domain() - Unregister Energy Model 
> (EM) for a device
> + * @dev		: Device for which the EM is registered
> + *
> + * Try to unregister the EM for the specified device (it checks 
> current
> + * reference counter). The EM for CPUs will not be freed.
> + */
> +void em_dev_unregister_perf_domain(struct device *dev)
> +{
> +	struct em_device *em_dev, *tmp;
> +
> +	if (IS_ERR_OR_NULL(dev))
> +		return;
> +
> +	/* We don't support freeing CPU structures in hotplug */
> +	if (_is_cpu_device(dev)) {
> +		dev_dbg_once(dev, "EM: the structures are not going to be 
> removed\n");
> +		return;
> +	}
> +
> +	mutex_lock(&em_pd_mutex);
> +
> +	if (list_empty(&em_pd_dev_list)) {
> +		mutex_unlock(&em_pd_mutex);
> +		return;
> +	}
> +
> +	list_for_each_entry_safe(em_dev, tmp, &em_pd_dev_list, 
> em_dev_list) {
> +		if (em_dev->dev == dev) {
> +			kref_put(&em_dev->kref, _em_release);
> +			break;
> +		}
> +	}
> +
> +	mutex_unlock(&em_pd_mutex);
> +}
> +EXPORT_SYMBOL_GPL(em_dev_unregister_perf_domain);

Ok, so em_dev_unregister_perf_domain() does not support the CPU 
device
and a subsequent em_register_perf_domain() will fail with EEXIST.

Is there a way to unregister/change the CPU's energy model during
runtime without restarting the whole system?