iio: health: max30100: Add DT pulse-width support

The appropriate LED pulse width for the MAX30100 depends on board-specific optical and mechanical design (lens, enclosure, LED-to-sensor distance) and the trade-off between measurement resolution and power consumption. Encoding it in Device Tree documents these platform choices and ensures consistent behavior.

Tested on: Raspberry Pi 3B + MAX30100 breakout board.

Signed-off-by Shrikant Raskar <[email protected]>

Changes since v1:
Add unit suffix.
Drop redundant description.

Link to v1:
https://lore.kernel.org/all/[email protected]/

---
 .../devicetree/bindings/iio/health/maxim,max30100.yaml      | 6 ++++++
 1 file changed, 6 insertions(+)

My bot found errors running 'make dt_binding_check' on your patch:

yamllint warnings/errors:

dtschema/dtc warnings/errors:
/builds/robherring/dt-review-ci/linux/Documentation/devicetree/bindings/iio/health/maxim,max30100.yaml: properties:maxim,pulse-width-us: 'enum' should not be valid under {'enum': ['const', 'enum', 'exclusiveMaximum', 'exclusiveMinimum', 'minimum', 'maximum', 'multipleOf', 'pattern']}
hint: Scalar and array keywords cannot be mixed
from schema $id: http://devicetree.org/meta-schemas/keywords.yaml#
/builds/robherring/dt-review-ci/linux/Documentation/devicetree/bindings/iio/health/maxim,max30100.yaml: properties:maxim,pulse-width-us: 'anyOf' conditional failed, one must be fixed:
'enum' is not one of ['maxItems', 'description', 'deprecated']
hint: Only "maxItems" is required for a single entry if there are no constraints defined for the values.
Additional properties are not allowed ('enum' was unexpected)
hint: Arrays must be described with a combination of minItems/maxItems/items
'maxItems' is not one of ['description', 'deprecated', 'const', 'enum', 'minimum', 'maximum', 'multipleOf', 'default', '$ref', 'oneOf']
1 is less than the minimum of 2
hint: Arrays must be described with a combination of minItems/maxItems/items
hint: cell array properties must define how many entries and what the entries are when there is more than one entry.
from schema $id: http://devicetree.org/meta-schemas/core.yaml#

doc reference errors (make refcheckdocs):

See https://patchwork.ozlabs.org/project/devicetree-bindings/patch/[email protected]

The base for the series is generally the latest rc1. A different dependency should be noted in *this* patch.

If you already ran 'make dt_binding_check' and didn't see the above error(s), then make sure 'yamllint' is installed and dt-schema is up to date:

pip3 install dtschema --upgrade

Please check and re-submit after running the above command yourself. Note that DT_SCHEMA_FILES can be set to your schema file to speed up checking your schema. However, it must be unset to test all examples with your schema.

The appropriate LED pulse width for the MAX30100 depends on board-specific optical and mechanical design (lens, enclosure, LED-to-sensor distance) and the trade-off between measurement resolution and power consumption. Encoding it in Device Tree documents these platform choices and ensures consistent behavior.

Tested on: Raspberry Pi 3B + MAX30100 breakout board.

Signed-off-by Shrikant Raskar <[email protected]>

Changes since v1:
Add unit suffix.
Drop redundant description.

Link to v1:
https://lore.kernel.org/all/[email protected]/

Quoted 6 lines

Signed-off-by Shrikant Raskar <[email protected]>

Changes since v1:
Add unit suffix.
Drop redundant description.

Quoted 2 lines

Link to v1:
https://lore.kernel.org/all/[email protected]/

This does not belong to commit msg but to changelog under ---.

See submitting patches.

You need to also start testing your patches BEFORE you send them.

The appropriate LED pulse width for the MAX30100 depends on board-specific optical and mechanical design (lens, enclosure, LED-to-sensor distance) and the trade-off between measurement resolution and power consumption. Encoding it in Device Tree documents these platform choices and ensures consistent behavior.

Tested on: Raspberry Pi 3B + MAX30100 breakout board.

Signed-off-by Shrikant Raskar <[email protected]>

Changes since v1:
Add unit suffix.
Drop redundant description.

Link to v1:
https://lore.kernel.org/all/[email protected]/

---
 .../devicetree/bindings/iio/health/maxim,max30100.yaml      | 6 ++++++
 1 file changed, 6 insertions(+)

Documentation/devicetree/bindings/iio/health/maxim,max30100.yaml +0 -0

index 967778fb0ce8..5c651a0151cc 100644

Documentation/devicetree/bindings/iio/health/maxim,max30100.yaml +2 -0

+
 additionalProperties: false
 
 required:

@@ -44,6 +49,7 @@ examples:
             compatible = "maxim,max30100";
             reg = <0x57>;
             maxim,led-current-microamp = <24000 50000>;
+            maxim,pulse-width-us = <1600>;
             interrupt-parent = <&gpio1>;
             interrupts = <16 2>;
         };

Quoted 28 lines · Shrikant Raskar

The appropriate LED pulse width for the MAX30100 depends on board-specific optical and mechanical design (lens, enclosure, LED-to-sensor distance) and the trade-off between measurement resolution and power consumption. Encoding it in Device Tree documents these platform choices and ensures consistent behavior.

Tested on: Raspberry Pi 3B + MAX30100 breakout board.

Signed-off-by Shrikant Raskar <[email protected]>

Changes since v1:
Add unit suffix.
Drop redundant description.

Link to v1:
https://lore.kernel.org/all/[email protected]/

---
 .../devicetree/bindings/iio/health/maxim,max30100.yaml      | 6 ++++++
 1 file changed, 6 insertions(+)

Documentation/devicetree/bindings/iio/health/maxim,max30100.yaml +0 -0

index 967778fb0ce8..5c651a0151cc 100644
@@ -27,6 +27,11 @@ properties:
       LED current whilst the engine is running. First indexed value is
       the configuration for the RED LED, and second value is for the IR LED.
 

Documentation/devicetree/bindings/iio/health/maxim,max30100.yaml properties: · line 32

Quoted 3 lines

Documentation/devicetree/bindings/iio/health/maxim,max30100.yaml +3 -0

+  maxim,pulse-width-us:
+    maxItems: 1
+    description: Pulse width in microseconds

Would be nice to add to the description which pulse width this is referring to.

Documentation/devicetree/bindings/iio/health/maxim,max30100.yaml properties: · line 33

Quoted 1 line

Documentation/devicetree/bindings/iio/health/maxim,max30100.yaml +1 -0

+    enum: [200, 400, 800, 1600]

Properties with standard unit suffixes are u32 arrays, so I think this would fix the error and also make maxItems not necessary.

items:
- enum: [200, 400, 800, 1600]

And we want to know what the default is if this property is omitted.

        default: 1600

Quoted 12 lines

Documentation/devicetree/bindings/iio/health/maxim,max30100.yaml +2 -0

+
 additionalProperties: false
 
 required:

@@ -44,6 +49,7 @@ examples:
             compatible = "maxim,max30100";
             reg = <0x57>;
             maxim,led-current-microamp = <24000 50000>;
+            maxim,pulse-width-us = <1600>;
             interrupt-parent = <&gpio1>;
             interrupts = <16 2>;
         };

The appropriate LED pulse width for the MAX30100 depends on board-specific optical and mechanical design (lens, enclosure, LED-to-sensor distance) and the trade-off between measurement resolution and power consumption. Encoding it in Device Tree documents these platform choices and ensures consistent behavior.

Tested on: Raspberry Pi 3B + MAX30100 breakout board.

Signed-off-by Shrikant Raskar <[email protected]>

Changes since v1:
Add unit suffix.
Drop redundant description.

Link to v1:
https://lore.kernel.org/all/[email protected]/

---
 .../devicetree/bindings/iio/health/maxim,max30100.yaml      | 6 ++++++
 1 file changed, 6 insertions(+)

Documentation/devicetree/bindings/iio/health/maxim,max30100.yaml +0 -0

index 967778fb0ce8..5c651a0151cc 100644

Documentation/devicetree/bindings/iio/health/maxim,max30100.yaml +3 -0

+    enum: [200, 400, 800, 1600]
+
 additionalProperties: false
 
 required:

@@ -44,6 +49,7 @@ examples:
             compatible = "maxim,max30100";
             reg = <0x57>;
             maxim,led-current-microamp = <24000 50000>;
+            maxim,pulse-width-us = <1600>;
             interrupt-parent = <&gpio1>;
             interrupts = <16 2>;
         };

Quoted 28 lines · On Wed, 8 Oct 2025 08:47:36 +0530 Shrikant Raskar <[email protected]>…

The appropriate LED pulse width for the MAX30100 depends on board-specific optical and mechanical design (lens, enclosure, LED-to-sensor distance) and the trade-off between measurement resolution and power consumption. Encoding it in Device Tree documents these platform choices and ensures consistent behavior.

Tested on: Raspberry Pi 3B + MAX30100 breakout board.

Signed-off-by Shrikant Raskar <[email protected]>

Changes since v1:
Add unit suffix.
Drop redundant description.

Link to v1:
https://lore.kernel.org/all/[email protected]/

---
 .../devicetree/bindings/iio/health/maxim,max30100.yaml      | 6 ++++++
 1 file changed, 6 insertions(+)

Documentation/devicetree/bindings/iio/health/maxim,max30100.yaml +0 -0

index 967778fb0ce8..5c651a0151cc 100644
@@ -27,6 +27,11 @@ properties:
       LED current whilst the engine is running. First indexed value is
       the configuration for the RED LED, and second value is for the IR LED.
 

Documentation/devicetree/bindings/iio/health/maxim,max30100.yaml properties: · line 32

Quoted 3 lines

Documentation/devicetree/bindings/iio/health/maxim,max30100.yaml +3 -0

+  maxim,pulse-width-us:
+    maxItems: 1
+    description: Pulse width in microseconds

I continued the discussion on v1 but just to make sure it is not missed, add a bit more here briefly touching on factors that govern what the right value is here.

Quoted 14 lines

Documentation/devicetree/bindings/iio/health/maxim,max30100.yaml +3 -0

+    enum: [200, 400, 800, 1600]
+
 additionalProperties: false
 
 required:

@@ -44,6 +49,7 @@ examples:
             compatible = "maxim,max30100";
             reg = <0x57>;
             maxim,led-current-microamp = <24000 50000>;
+            maxim,pulse-width-us = <1600>;
             interrupt-parent = <&gpio1>;
             interrupts = <16 2>;
         };

The MAX30100 driver previously hardcoded the SPO2 pulse width to 1600us. This patch adds support for reading the pulse width from device tree (maxim,pulse-width-us) and programming it into the SPO2 configuration register.

If no property is provided, the driver falls back to 1600us to preserve existing behavior.

Testing:
Hardware: Raspberry Pi 3B + MAX30100 breakout
Verified DT property read in probe()
Confirmed SPO2_CONFIG register written correctly using regmap_read()

Signed-off-by Shrikant Raskar <[email protected]>

Changes since v1:
Use FIELD_PREP() and define a pulse width bit mask. Initialize default pulse_us before property read. Use dev_err_probe() for error reporting.
Make pulse_width signed to handle negative return values.

Link to v1:
https://lore.kernel.org/all/[email protected]/

---
 drivers/iio/health/max30100.c | 35 +++++++++++++++++++++++++++++++++--

 1 file changed, 33 insertions(+), 2 deletions(-)

drivers/iio/health/max30100.c +0 -1

index 814f521e47ae..50cd4fd13849 100644
@@ -5,7 +5,6 @@
   * Copyright (C) 2015, 2018
   * Author: Matt Ranostay <[email protected]>
   *
- * TODO: enable pulse length controls via device tree properties
   */

 #include <linux/module.h>

drivers/iio/health/max30100.c +4 -0

@@ -54,6 +53,10 @@
  #define MAX30100_REG_SPO2_CONFIG		0x07
  #define MAX30100_REG_SPO2_CONFIG_100HZ		BIT(2)
  #define MAX30100_REG_SPO2_CONFIG_HI_RES_EN	BIT(6)
+#define MAX30100_REG_SPO2_CONFIG_PW_MASK	GENMASK(1, 0)
+#define MAX30100_REG_SPO2_CONFIG_200US		0x0
+#define MAX30100_REG_SPO2_CONFIG_400US		0x1
+#define MAX30100_REG_SPO2_CONFIG_800US		0x2
  #define MAX30100_REG_SPO2_CONFIG_1600US		0x3

 #define MAX30100_REG_LED_CONFIG 0x09

drivers/iio/health/max30100.c +0 -0

@@ -306,19 +309,47 @@ static int max30100_led_init(struct max30100_data *data)
  		MAX30100_REG_LED_CONFIG_LED_MASK, reg);
  }

drivers/iio/health/max30100.c +16 -0

+static int max30100_get_pulse_width(unsigned int pwidth_us)
+{
+	switch (pwidth_us) {
+	case 200:
+		return MAX30100_REG_SPO2_CONFIG_200US;
+	case 400:
+		return MAX30100_REG_SPO2_CONFIG_400US;
+	case 800:
+		return MAX30100_REG_SPO2_CONFIG_800US;
+	case 1600:
+		return MAX30100_REG_SPO2_CONFIG_1600US;
+	default:
+		return -EINVAL;
+	}
+}
+

 static int max30100_chip_init(struct max30100_data *data) {
  int ret;

drivers/iio/health/max30100.c +4 -0

+	int pulse_width;
+	/* set default pulse-width-us to 1600us */
+	unsigned int pulse_us = 1600;
+	struct device *dev = &data->client->dev;

  /* setup LED current settings */
  ret = max30100_led_init(data);
  if (ret)
  return ret;

drivers/iio/health/max30100.c +6 -0

+	/* Read pulse-width-us from DT */
+	device_property_read_u32(dev, "maxim,pulse-width-us", &pulse_us);
+
+	pulse_width = max30100_get_pulse_width(pulse_us);
+	if (pulse_width < 0)
+		return dev_err_probe(dev, pulse_width, "invalid pulse-width

%uus\n", pulse_us);
+
  /* enable hi-res SPO2 readings at 100Hz */
  ret = regmap_write(data->regmap, MAX30100_REG_SPO2_CONFIG, MAX30100_REG_SPO2_CONFIG_HI_RES_EN |

drivers/iio/health/max30100.c +2 -1

-				 MAX30100_REG_SPO2_CONFIG_100HZ);
+				 MAX30100_REG_SPO2_CONFIG_100HZ |
+				 FIELD_PREP(MAX30100_REG_SPO2_CONFIG_PW_MASK,

pulse_width));
  if (ret)
  return ret;

Hi Shrikant,

Thanks for your patch.

Quoted 21 lines · Shrikant Raskar

The MAX30100 driver previously hardcoded the SPO2 pulse width to 1600us. This patch adds support for reading the pulse width from device tree (maxim,pulse-width-us) and programming it into the SPO2 configuration register.

If no property is provided, the driver falls back to 1600us to preserve existing behavior.

Testing:
Hardware: Raspberry Pi 3B + MAX30100 breakout
Verified DT property read in probe()
Confirmed SPO2_CONFIG register written correctly using regmap_read()

Signed-off-by Shrikant Raskar <[email protected]>

Changes since v1:
Use FIELD_PREP() and define a pulse width bit mask. Initialize default pulse_us before property read. Use dev_err_probe() for error reporting.
Make pulse_width signed to handle negative return values.

Quoted 2 lines

Link to v1:
https://lore.kernel.org/all/[email protected]/

As mentioned in the bindings patch, this is not place for changelog. With that fixed:

Reviewed-by Nuno Sá <[email protected]>

Quoted 79 lines

---
 drivers/iio/health/max30100.c | 35 +++++++++++++++++++++++++++++++++--
 1 file changed, 33 insertions(+), 2 deletions(-)

drivers/iio/health/max30100.c +33 -2

index 814f521e47ae..50cd4fd13849 100644
@@ -5,7 +5,6 @@
  * Copyright (C) 2015, 2018
  * Author: Matt Ranostay <[email protected]>
  *
- * TODO: enable pulse length controls via device tree properties
  */
 
 #include <linux/module.h>

@@ -54,6 +53,10 @@
 #define MAX30100_REG_SPO2_CONFIG             0x07
 #define MAX30100_REG_SPO2_CONFIG_100HZ               BIT(2)
 #define MAX30100_REG_SPO2_CONFIG_HI_RES_EN   BIT(6)
+#define MAX30100_REG_SPO2_CONFIG_PW_MASK     GENMASK(1, 0)
+#define MAX30100_REG_SPO2_CONFIG_200US               0x0
+#define MAX30100_REG_SPO2_CONFIG_400US               0x1
+#define MAX30100_REG_SPO2_CONFIG_800US               0x2
 #define MAX30100_REG_SPO2_CONFIG_1600US              0x3
 
 #define MAX30100_REG_LED_CONFIG                      0x09

@@ -306,19 +309,47 @@ static int max30100_led_init(struct max30100_data *data)
              MAX30100_REG_LED_CONFIG_LED_MASK, reg);
 }
 
+static int max30100_get_pulse_width(unsigned int pwidth_us)
+{
+     switch (pwidth_us) {
+     case 200:
+             return MAX30100_REG_SPO2_CONFIG_200US;
+     case 400:
+             return MAX30100_REG_SPO2_CONFIG_400US;
+     case 800:
+             return MAX30100_REG_SPO2_CONFIG_800US;
+     case 1600:
+             return MAX30100_REG_SPO2_CONFIG_1600US;
+     default:
+             return -EINVAL;
+     }
+}
+
 static int max30100_chip_init(struct max30100_data *data)
 {
      int ret;
+     int pulse_width;
+     /* set default pulse-width-us to 1600us */
+     unsigned int pulse_us = 1600;
+     struct device *dev = &data->client->dev;
 
      /* setup LED current settings */
      ret = max30100_led_init(data);
      if (ret)
              return ret;
 
+     /* Read pulse-width-us from DT */
+     device_property_read_u32(dev, "maxim,pulse-width-us", &pulse_us);
+
+     pulse_width = max30100_get_pulse_width(pulse_us);
+     if (pulse_width < 0)
+             return dev_err_probe(dev, pulse_width, "invalid pulse-width
 %uus\n", pulse_us);
+
      /* enable hi-res SPO2 readings at 100Hz */
      ret = regmap_write(data->regmap, MAX30100_REG_SPO2_CONFIG,
                               MAX30100_REG_SPO2_CONFIG_HI_RES_EN |
-                              MAX30100_REG_SPO2_CONFIG_100HZ);
+                              MAX30100_REG_SPO2_CONFIG_100HZ |
+                              FIELD_PREP(MAX30100_REG_SPO2_CONFIG_PW_MASK,
 pulse_width));
      if (ret)

              return ret;

drivers/iio/health/max30100.c +0 -1

@@ -5,7 +5,6 @@
  * Copyright (C) 2015, 2018
  * Author: Matt Ranostay <[email protected]>
  *
- * TODO: enable pulse length controls via device tree properties
  */
 
 #include <linux/module.h>