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

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

[Andy Shevchenko]

On Thu, Sep 25, 2025 at 09:54:19AM +0200, Romain Gantois wrote:
> On Tuesday, 16 September 2025 16:27:25 CEST Romain Gantois wrote:
> > 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:
...
> > > > 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.
> 
> My mistake, this cast is required to avoid a compiler warning;

THen provide a proper specifier instead. Casting in printf() is in 99.9% cases
just a pure mistake.

-- 
With Best Regards,
Andy Shevchenko

[PATCH 0/4] Add support for the LTM8054 voltage regulator

[Romain Gantois]

Hello everyone,

This series adds initial support of the Linear Technology LTM8054 voltage
regulator. The driver supports a fixed voltage and a tunable output current
limit using a DAC-controlled pin.

I'd say that the only unusual part of this series is the usage of the IIO
consumer API in a regulator driver. I think this makes sense here, since
the regulator driver has to access a DAC to read/set the output current
limit.

Since the regulator driver writes microvolts and the IIO consumer API takes
millivolts, the reads and writes to the CTL DAC have to be scaled by a
factor of 1000. Scaled reads are already supported in IIO, but scaled
writes are not, which is why I've implemented them in patch 2/4.

Please let me know what you think.

Thanks,

Romain

Signed-off-by: Romain Gantois <romain.gantois@bootlin.com>
---
Romain Gantois (4):
      regulator: dt-bindings: Add Linear Technology LTM8054 regulator
      iio: add processed write API
      regulator: Support the LTM8054 voltage regulator
      regulator: ltm8054: Support output current limit control

 .../bindings/regulator/lltc,ltm8054.yaml           |  77 +++++++
 MAINTAINERS                                        |   6 +
 drivers/iio/inkern.c                               |  99 +++++++++
 drivers/regulator/Kconfig                          |   9 +
 drivers/regulator/Makefile                         |   1 +
 drivers/regulator/ltm8054-regulator.c              | 229 +++++++++++++++++++++
 include/linux/iio/consumer.h                       |  17 ++
 7 files changed, 438 insertions(+)
---
base-commit: f87c2b34768828c4ff535ba7d50dd938838caab9
change-id: 20250728-ltm8054-driver-11cfa4741065

Best regards,
-- 
Romain Gantois <romain.gantois@bootlin.com>

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

[Romain Gantois]

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.

Signed-off-by: Romain Gantois <romain.gantois@bootlin.com>
---
 drivers/regulator/Kconfig             |   1 +
 drivers/regulator/ltm8054-regulator.c | 109 ++++++++++++++++++++++++++++++++++
 2 files changed, 110 insertions(+)

diff --git a/drivers/regulator/Kconfig b/drivers/regulator/Kconfig
index 15fb71193b67d0b2daa631b69778dde9323aedd2..22cf0e980351f21e3ef5b6611a39cb48aeb503ea 100644
--- a/drivers/regulator/Kconfig
+++ b/drivers/regulator/Kconfig
@@ -579,6 +579,7 @@ config REGULATOR_LTC3676
 
 config REGULATOR_LTM8054
 	tristate "LTM8054 Buck-Boost voltage regulator"
+	depends on IIO
 	help
 	  This driver provides support for the Linear Technology LTM8054
 	  Buck-Boost micromodule regulator. The LTM8054 has an adjustable
diff --git a/drivers/regulator/ltm8054-regulator.c b/drivers/regulator/ltm8054-regulator.c
index e41bd95da55fb87912e2cdf70bae231133c25745..3b7b826e29cfb37415a7fb7cab678cc33494d184 100644
--- a/drivers/regulator/ltm8054-regulator.c
+++ b/drivers/regulator/ltm8054-regulator.c
@@ -11,12 +11,27 @@
 #include <linux/regulator/driver.h>
 #include <linux/regulator/of_regulator.h>
 #include <linux/platform_device.h>
+#include <linux/iio/consumer.h>
+#include <linux/iio/types.h>
 #include <linux/gpio/consumer.h>
 
+/* Threshold voltage between the Vout and Iout pins which triggers current
+ * limiting, in microvolts
+ */
+#define LTM8054_VOUT_IOUT_MAX 58000
+
+#define LTM8054_MAX_CTL_V 1200000
+#define LTM8054_MIN_CTL_V 50000
+
 /* The LTM8054 regulates its FB pin to 1.2V */
 #define LTM8054_FB_V 1200000
 
 struct ltm8054_priv {
+	struct iio_channel *ctl_dac;
+
+	int min_uA;
+	int max_uA;
+
 	struct regulator_desc rdesc;
 };
 
@@ -30,18 +45,105 @@ static int ltm8054_scale(unsigned int uV, u32 r1, u32 r2)
 	return uV + (unsigned int)tmp;
 }
 
+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);
+
+	/* Standard IIO voltage unit is mV, scale accordingly. */
+	return iio_write_channel_processed_scale(priv->ctl_dac, vdac_uV, 1000);
+}
+
+static int ltm8054_get_current_limit(struct regulator_dev *rdev)
+{
+	struct ltm8054_priv *priv = rdev_get_drvdata(rdev);
+	int ret, vdac_uv;
+	u64 uA;
+
+	ret = iio_read_channel_processed_scale(priv->ctl_dac, &vdac_uv, 1000);
+	if (ret < 0) {
+		dev_err(&rdev->dev, "failed to read CTL DAC voltage, err %d\n", ret);
+		return ret;
+	}
+
+	uA = (u64)vdac_uv * priv->max_uA;
+	do_div(uA, LTM8054_MAX_CTL_V);
+
+	return uA;
+}
+
 static const struct regulator_ops ltm8054_regulator_ops = {
+	.set_current_limit = ltm8054_set_current_limit,
+	.get_current_limit = ltm8054_get_current_limit,
 };
 
+static int ltm8054_init_ctl_dac(struct platform_device *pdev, struct ltm8054_priv *priv)
+{
+	struct iio_channel *ctl_dac;
+	enum iio_chan_type type;
+	int ret;
+
+	ctl_dac = devm_iio_channel_get(&pdev->dev, "ctl");
+	if (IS_ERR(ctl_dac))
+		return PTR_ERR(ctl_dac);
+
+	ret = iio_get_channel_type(ctl_dac, &type);
+	if (ret < 0)
+		return ret;
+
+	if (type != IIO_VOLTAGE)
+		return -EINVAL;
+
+	priv->ctl_dac = ctl_dac;
+
+	return 0;
+}
+
 static int ltm8054_of_parse(struct device *dev, struct ltm8054_priv *priv,
 			    struct regulator_config *config)
 {
 	struct device_node *np = dev->of_node;
+	u32 rsense;
 	u32 r[2];
+	u64 tmp;
 	int ret;
 
 	config->of_node = np;
 
+	ret = of_property_read_u32(np, "lltc,iout-rsense-micro-ohms", &rsense);
+	if (ret < 0) {
+		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;
+	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
+	 */
+
+	tmp = LTM8054_MIN_CTL_V * (u64)priv->max_uA;
+	do_div(tmp, (u32)LTM8054_MAX_CTL_V);
+	priv->min_uA = tmp;
+
 	ret = of_property_read_u32_array(np, "lltc,fb-voltage-divider", r, 2);
 	if (ret) {
 		dev_err(dev, "Failed to parse voltage divider\n");
@@ -52,6 +154,9 @@ static int ltm8054_of_parse(struct device *dev, struct ltm8054_priv *priv,
 	priv->rdesc.min_uV = priv->rdesc.fixed_uV;
 	priv->rdesc.n_voltages = 1;
 
+	dev_dbg(dev, "max_uA: %d min_uA: %d fixed_uV: %d\n",
+		priv->max_uA, priv->min_uA, priv->rdesc.fixed_uV);
+
 	config->init_data = of_get_regulator_init_data(dev,
 						       np,
 						       &priv->rdesc);
@@ -92,6 +197,10 @@ static int ltm8054_probe(struct platform_device *pdev)
 	if (ret)
 		return dev_err_probe(&pdev->dev, ret, "failed to parse device tree\n");
 
+	ret = ltm8054_init_ctl_dac(pdev, priv);
+	if (ret)
+		return dev_err_probe(&pdev->dev, ret, "failed to initialize CTL DAC\n");
+
 	rdev = devm_regulator_register(&pdev->dev, &priv->rdesc, &config);
 	if (IS_ERR(rdev))
 		return dev_err_probe(&pdev->dev, PTR_ERR(rdev), "failed to register regulator\n");

-- 
2.51.0

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

[Andy Shevchenko]

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

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

[Romain Gantois]

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

[Andy Shevchenko]

On Tue, Sep 16, 2025 at 04:27:25PM +0200, Romain Gantois wrote:
> 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:

First of all, please remove unneeded context (which is assumed you agree with)
in the replies. It makes reviewers' life much easier.

...

> > /*
> >  * 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.

It's better to read in a way of

	tmp = (u64)priv->max_uA * LTM8054_MIN_CTL_mV;

-- 
With Best Regards,
Andy Shevchenko

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

[Andy Shevchenko]

On Wed, Sep 17, 2025 at 10:02:03AM +0300, Andy Shevchenko wrote:
> On Tue, Sep 16, 2025 at 04:27:25PM +0200, Romain Gantois wrote:
> > 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:

...

> > > /*
> > >  * 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.
> 
> It's better to read in a way of
> 
> 	tmp = (u64)priv->max_uA * LTM8054_MIN_CTL_mV;

I just realised that in previous mails and here I meant _uV postfix for the
predefined voltage thresholds. Sorry for the confusion.

-- 
With Best Regards,
Andy Shevchenko

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

[Romain Gantois]

[-- Attachment #1: Type: text/plain, Size: 661 bytes --]

On Tuesday, 16 September 2025 16:27:25 CEST Romain Gantois wrote:
> 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:
...
> > > 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.

My mistake, this cast is required to avoid a compiler warning;

Thanks,

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

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