linux-kernel - [PATCH v3 1/2] dt-bindings: iio: health: max30100: Add LED pulse-width property

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Message-ID: <20251012173035.12536-2-raskar.shree97@gmail.com>
Date: Sun, 12 Oct 2025 23:00:34 +0530
From: Shrikant Raskar <raskar.shree97@...il.com>
To: jic23@...nel.org,
	robh@...nel.org,
	krzk+dt@...nel.org,
	conor+dt@...nel.org
Cc: dlechner@...libre.com,
	nuno.sa@...log.com,
	andy@...nel.org,
	matt@...ostay.sg,
	skhan@...uxfoundation.org,
	david.hunter.linux@...il.com,
	linux-iio@...r.kernel.org,
	devicetree@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	linux-kernel-mentees@...ts.linux.dev,
	Shrikant Raskar <raskar.shree97@...il.com>
Subject: [PATCH v3 1/2] dt-bindings: iio: health: max30100: Add LED pulse-width property

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.

Signed-off-by: Shrikant Raskar <raskar.shree97@...il.com>
---
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/20251008031737.7321-2-raskar.shree97@gmail.com/
---
 .../devicetree/bindings/iio/health/maxim,max30100.yaml    | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/Documentation/devicetree/bindings/iio/health/maxim,max30100.yaml b/Documentation/devicetree/bindings/iio/health/maxim,max30100.yaml
index 967778fb0ce8..d4753c85ecc3 100644
--- a/Documentation/devicetree/bindings/iio/health/maxim,max30100.yaml
+++ b/Documentation/devicetree/bindings/iio/health/maxim,max30100.yaml
@@ -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