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

Romain Gantois
2025-09-16T14:27:33Z

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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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