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

Add Device Tree support for configuring the LED pulse-width of the MAX30100 sensor, and updates the driver to read and apply this property.

Testing:
- Verify DT property read successfully in probe().
- Verify default fallback to 1600 us when DT property is omitted.
- Confirm SPO2_CONFIG register programmed correctly using regmap_read().
- Validate different DT pulse-width values (200, 400, 800, 1600 us) are applied correctly.
- Validate probe() failure for invalid LED pulse-width
- Tested-on: Raspberry Pi 3B + MAX30100 breakout board

Changelog:
Changes from v2:
- Fix DT binding schema errors
- Add default value
- Remove changelog from commit message
- Add missing header file

Shrikant Raskar (2):
dt-bindings: iio: health: max30100: Add LED pulse-width property
iio: health: max30100: Make LED pulse-width configurable via DT

 .../bindings/iio/health/maxim,max30100.yaml   |  8 ++++
 drivers/iio/health/max30100.c                 | 38 +++++++++++++++++--
 2 files changed, 43 insertions(+), 3 deletions(-)

base-commit: 8bd9238e511d02831022ff0270865c54ccc482d6

2.43.0

The LED pulse width on the MAX30100 sensor determines how long the IR/Red LEDs are driven during each sample, directly affecting the emitted optical energy and hence the received signal amplitude.

This parameter is highly dependent on the mechanical and optical integration of the sensor, such as:
- The type and thickness of the optical window or lens covering the sensor.
- The distance between the LED and photodiode.
- The reflectivity of the target surface.

For example:
- A smartwatch or wearable ring with a thin glass window can operate with shorter pulses (200-400 us) to save power.
- A medical-grade pulse oximeter or sensor mounted behind a thicker protective layer may require longer pulses (800-1600 us) for reliable signal amplitude.

Because this configuration is determined by hardware design rather than by runtime conditions, it is appropriate to describe it in the DT.

If not specified, the driver defaults to 1600 us to maintain existing behavior.

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

---
Changelog:
Changes since v2:
- Fix DT binding schema for maxim,pulse-width-us
- Remove maxItems
- Update description with additional details
- Add default value to specify fallback pulse width when property is omitted
- Remove redundant changelog from commit message

Link to v2:
https://lore.kernel.org/all/[email protected]/

---
 .../devicetree/bindings/iio/health/maxim,max30100.yaml    | 8 ++++++++
 1 file changed, 8 insertions(+)

index 967778fb0ce8..d4753c85ecc3 100644
@@ -27,6 +27,14 @@ 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.
 
+  maxim,pulse-width-us:
+    description: |
+      LED pulse width in microseconds. Appropriate pulse width depends on
+      factors such as optical window absorption, LED-to-sensor distance,
+      and expected reflectivity of the skin or contact surface.
+    enum: [200, 400, 800, 1600]
+    default: 1600
+
 additionalProperties: false
 
 required:

2.43.0

Best regards,
Krzysztof

The required LED pulse width depends on board-specific optical and mechanical design, which affects measurement accuracy and power use. Making it configurable via Device Tree allows each platform to define an appropriate value instead of relying on a hardcoded default.

If unspecified, the driver defaults to 1600 us for backward compatibility.

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

---
Changelog:
Changes since v2:
- Reorder SPO2_CONFIG register defines by bit position (lowest to highest).
- Add missing header file for FIELD_PREP() macro.
- Add Reviewed-by tag.

Link to v2:
https://lore.kernel.org/all/[email protected]/

---
 drivers/iio/health/max30100.c | 38 ++++++++++++++++++++++++++++++++---
 1 file changed, 35 insertions(+), 3 deletions(-)

index 814f521e47ae..3d441013893c 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>

@@ -18,6 +17,7 @@
 #include <linux/mutex.h>
 #include <linux/property.h>
 #include <linux/regmap.h>
+#include <linux/bitfield.h>
 #include <linux/iio/iio.h>
 #include <linux/iio/buffer.h>
 #include <linux/iio/kfifo_buf.h>

@@ -52,9 +52,13 @@
 #define MAX30100_REG_MODE_CONFIG_PWR		BIT(7)
 
 #define MAX30100_REG_SPO2_CONFIG		0x07
+#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_SPO2_CONFIG_100HZ		BIT(2)
 #define MAX30100_REG_SPO2_CONFIG_HI_RES_EN	BIT(6)
-#define MAX30100_REG_SPO2_CONFIG_1600US		0x3
 
 #define MAX30100_REG_LED_CONFIG			0x09
 #define MAX30100_REG_LED_CONFIG_LED_MASK	0x0f

@@ -306,19 +310,47 @@ 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 LED pulse-width to 1600 us */
+	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 LED 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 LED 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;
 

2.43.0

Applied to the togreg branch of iio.git and pushed out as testing for now

Thanks,

Jonathan

Thanks for the update. I really appreciate your time and support!

Regards,
Shrikant