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

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Message-ID: <8772650.T7Z3S40VBb@fw-rgant>
Date: Tue, 16 Sep 2025 16:27:25 +0200
From: Romain Gantois <romain.gantois@...tlin.com>
To: Andy Shevchenko <andriy.shevchenko@...el.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 Tuesday, 16 September 2025 15:19:16 CEST Andy Shevchenko wrote:
> 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?
> 

This one is indeed unnecessary.

> > +	/* 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;

This cast avoids an overflow of the multiplication, since the result may 
easily exceed 32 bytes in size.

> > +	do_div(tmp, (u32)LTM8054_MAX_CTL_V);
> 
> Why casting?

Since do_div() is a macro, I casted the second argument just to be safe, but 
it seems that do_div() already does this internally, so I'll just drop the 
cast.

Thanks,

-- 
Romain Gantois, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com

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