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

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Message-ID: <ee686b83-d8ae-4643-8913-bd31de7f6534@kernel.org>
Date: Mon, 13 Oct 2025 02:06:21 +0200
From: Krzysztof Kozlowski <krzk@...nel.org>
To: Shrikant Raskar <raskar.shree97@...il.com>, 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
Subject: Re: [PATCH v3 1/2] dt-bindings: iio: health: max30100: Add LED
 pulse-width property

On 12/10/2025 19:30, Shrikant Raskar wrote:
> 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>

Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>

Best regards,
Krzysztof