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

Romain Gantois
2025-09-16T10:24:23Z

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