linux-kernel - Re: [RESEND][PATCH v2 3/4] PM: EM: Add em_dev_update_chip

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Message-ID: <eb9f48f6-cca8-405b-82a2-352893a79f14@arm.com>
Date: Tue, 26 Mar 2024 11:09:05 +0100
From: Dietmar Eggemann <dietmar.eggemann@....com>
To: Lukasz Luba <lukasz.luba@....com>, linux-kernel@...r.kernel.org,
 linux-pm@...r.kernel.org
Cc: linux-arm-kernel@...ts.infradead.org, sboyd@...nel.org, nm@...com,
 linux-samsung-soc@...r.kernel.org, daniel.lezcano@...aro.org,
 rafael@...nel.org, viresh.kumar@...aro.org, krzysztof.kozlowski@...aro.org,
 alim.akhtar@...sung.com, m.szyprowski@...sung.com, mhiramat@...nel.org
Subject: Re: [RESEND][PATCH v2 3/4] PM: EM: Add em_dev_update_chip_binning()

On 22/03/2024 12:08, Lukasz Luba wrote:

> diff --git a/kernel/power/energy_model.c b/kernel/power/energy_model.c
> index 6960dd7393b2d..f7f7ae34ec552 100644
> --- a/kernel/power/energy_model.c
> +++ b/kernel/power/energy_model.c
> @@ -808,3 +808,54 @@ static void em_update_workfn(struct work_struct *work)
>  {
>  	em_check_capacity_update();
>  }
> +
> +/**
> + * em_dev_update_chip_binning() - Update Energy Model with new values after

s/with new values// ... IMHO this should be obvious ?

> + *			the new voltage information is present in the OPPs.
> + * @dev		: Device for which the Energy Model has to be updated.
> + *
> + * This function allows to update easily the EM with new values available in
> + * the OPP framework and DT. It can be used after the chip has been properly
> + * verified by device drivers and the voltages adjusted for the 'chip binning'.
> + * It uses the "dynamic-power-coefficient" DT property to calculate the power
> + * values for EM. For power calculation it uses the new adjusted voltage
> + * values known for OPPs, which might be changed after boot.

The last two sentences describe what dev_pm_opp_calc_power() is doing.
Maybe this can be made clearer here?

> + */
> +int em_dev_update_chip_binning(struct device *dev)

This is the old dev_pm_opp_of_update_em() right?

> +{
> +	struct em_perf_table __rcu *em_table;
> +	struct em_perf_domain *pd;
> +	int i, ret;
> +
> +	if (IS_ERR_OR_NULL(dev))
> +		return -EINVAL;

When do you use if '(IS_ERR_OR_NULL(dev))' and when 'if(!dev)' for EM
interface functions?

> +	pd = em_pd_get(dev);
> +	if (!pd) {
> +		dev_warn(dev, "Couldn't find Energy Model\n");
> +		return -EINVAL;
> +	}
> +
> +	em_table = em_table_dup(pd);
> +	if (!em_table) {
> +		dev_warn(dev, "EM: allocation failed\n");
> +		return -ENOMEM;
> +	}
> +
> +	/* Update power values which might change due to new voltage in OPPs */
> +	for (i = 0; i < pd->nr_perf_states; i++) {
> +		unsigned long freq = em_table->state[i].frequency;
> +		unsigned long power;
> +
> +		ret = dev_pm_opp_calc_power(dev, &power, &freq);
> +		if (ret) {
> +			em_table_free(em_table);
> +			return ret;
> +		}
> +
> +		em_table->state[i].power = power;
> +	}
> +
> +	return em_recalc_and_update(dev, pd, em_table);
> +}
> +EXPORT_SYMBOL_GPL(em_dev_update_chip_binning);

In the previous version of 'chip-binning' you were using the new EM
interface em_dev_compute_costs() (1) which is now replaced by
em_recalc_and_update() -> em_compute_costs().

https://lkml.kernel.org/r/20231220110339.1065505-2-lukasz.luba@arm.com

Which leaves (1) still unused.

That was why my concern back then that we shouldn't introduce EM
interfaces without a user:

https://lkml.kernel.org/r/8fc499cf-fca1-4465-bff7-a93dfd36f3c8@arm.com

What happens now with em_dev_compute_costs()?