[PATCH v2 2/2] iio: health: max30100: Add pulse-width configuration via DT

[Shrikant Raskar <raskar.shree97@gmail.com>]

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 <raskar.shree97@gmail.com>

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/20251004015623.7019-3-raskar.shree97@gmail.com/
---
 drivers/iio/health/max30100.c | 35 +++++++++++++++++++++++++++++++++--
 1 file changed, 33 insertions(+), 2 deletions(-)

diff --git a/drivers/iio/health/max30100.c b/drivers/iio/health/max30100.c
index 814f521e47ae..50cd4fd13849 100644
--- a/drivers/iio/health/max30100.c
+++ b/drivers/iio/health/max30100.c
@@ -5,7 +5,6 @@
  * Copyright (C) 2015, 2018
  * Author: Matt Ranostay <matt.ranostay@konsulko.com>
  *
- * 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;
 
-- 
2.43.0