linux-kernel - Re: [PATCH 4/4] regulator: ltm8054: Support output current limit control

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Message-ID: <aMlj1OcfH8r9Zz6x@smile.fi.intel.com>
Date: Tue, 16 Sep 2025 16:19:16 +0300
From: Andy Shevchenko <andriy.shevchenko@...el.com>
To: Romain Gantois <romain.gantois@...tlin.com>
Cc: Liam Girdwood <lgirdwood@...il.com>, Mark Brown <broonie@...nel.org>,
	Rob Herring <robh@...nel.org>,
	Krzysztof Kozlowski <krzk+dt@...nel.org>,
	Conor Dooley <conor+dt@...nel.org>,
	Jonathan Cameron <jic23@...nel.org>,
	David Lechner <dlechner@...libre.com>,
	Nuno Sá <nuno.sa@...log.com>,
	Andy Shevchenko <andy@...nel.org>,
	Thomas Petazzoni <thomas.petazzoni@...tlin.com>,
	linux-kernel@...r.kernel.org, devicetree@...r.kernel.org,
	linux-iio@...r.kernel.org
Subject: Re: [PATCH 4/4] regulator: ltm8054: Support output current limit
 control

On Tue, Sep 16, 2025 at 12:24:09PM +0200, Romain Gantois wrote:
> The LTM8054 supports setting a fixed output current limit using a sense
> resistor connected to a dedicated pin. This limit can then be lowered
> dynamically by varying the voltage level of the CTL pin.
> 
> Support controlling the LTM8054's output current limit.

...

> in microvolts

Yeah, using _mV postfix will make it visible that those are in micro-Volts.

...

> +static int ltm8054_set_current_limit(struct regulator_dev *rdev, int min_uA, int max_uA)
> +{
> +	struct ltm8054_priv *priv = rdev_get_drvdata(rdev);
> +	u64 vdac_uV;
> +
> +	min_uA = clamp_t(int, min_uA, priv->min_uA, priv->max_uA);
> +
> +	/* adjusted current limit = Rsense current limit * CTL pin voltage / max CTL pin voltage */
> +	vdac_uV = (u64)min_uA * LTM8054_MAX_CTL_V;
> +	do_div(vdac_uV, priv->max_uA);
> +
> +	dev_dbg(&rdev->dev,
> +		"Setting current limit to %duA, CTL pin to %duV\n", min_uA, (int)vdac_uV);

Why casting?

> +	/* Standard IIO voltage unit is mV, scale accordingly. */
> +	return iio_write_channel_processed_scale(priv->ctl_dac, vdac_uV, 1000);
> +}

...

> +	ret = of_property_read_u32(np, "lltc,iout-rsense-micro-ohms", &rsense);

device_property_read_u32()

> +	if (ret < 0) {

Be consistent with a style, in the previous patch it was 'if (ret)'.

> +		dev_err(dev, "failed to get sense resistor value\n");
> +		return ret;
> +	}
> +
> +	if (rsense == 0) {
> +		dev_err(dev, "invalid value zero for sense resistor\n");
> +		return -EINVAL;
> +	}
> +
> +	/* The maximum output current limit is the one set by the Rsense resistor */
> +	tmp = 1000000 * (u64)LTM8054_VOUT_IOUT_MAX;

Yo may use MICRO and drop the casting.

> +	do_div(tmp, rsense);
> +	priv->max_uA = tmp;
> +
> +	/* Applying a voltage below LTM8054_MAX_CTL_V on the CTL pin reduces
> +	 * the output current limit. If this level drops below
> +	 * LTM8054_MIN_CTL_V the regulator stops switching
> +	 */

/*
 * Besides missing period at the end this is not correct multi-line style of
 * the comments. Use this example.
 */

> +	tmp = LTM8054_MIN_CTL_V * (u64)priv->max_uA;
> +	do_div(tmp, (u32)LTM8054_MAX_CTL_V);

Why casting?

> +	priv->min_uA = tmp;

-- 
With Best Regards,
Andy Shevchenko