Re: [PATCH 2/3] dt-bindings: iio: st,st-sensors: add st,fullscale-mg

[Conor Dooley <conor@kernel.org>]

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On Fri, Jun 05, 2026 at 12:08:42PM +0200, Herman van Hazendonk wrote:
> Add an optional st,fullscale-mg property that selects the initial
> full-scale range of an ST MEMS sensor at probe time, expressed in
> milligauss for magnetometers (and analogous engineering units for
> other ST sensor families that may grow this property in the future).
> 
> The property is purely additive: if absent, drivers fall back to
> their existing chip default, and if present but unsupported by the
> specific sensor the driver warns and falls back. No existing in-tree
> DTS is affected.
> 
> The motivating case is the LSM303DLH magnetometer on the HP TouchPad
> (apq8060 / tenderloin) where the kernel's chip-default +/-1.3 G range
> saturates the X axis to the chip's 0xF000 overflow sentinel out of
> probe, because the chip is mounted close to surrounding power planes
> and picks up enough DC bias to exceed the smallest range. The driver
> core hardcodes fs_avl[0] as the starting range, so userspace cannot
> recover without racing the driver to write the in_magn_x_scale sysfs
> attribute after probe. st,fullscale-mg lets the device tree declare
> a wider initial range up-front and avoids the race entirely.
> 
> Signed-off-by: Herman van Hazendonk <github.com@herrie.org>
> ---
>  .../devicetree/bindings/iio/st,st-sensors.yaml | 18 ++++++++++++++++++
>  1 file changed, 18 insertions(+)
> 
> diff --git a/Documentation/devicetree/bindings/iio/st,st-sensors.yaml b/Documentation/devicetree/bindings/iio/st,st-sensors.yaml
> index a1a958215cdb..335f38e9f78f 100644
> --- a/Documentation/devicetree/bindings/iio/st,st-sensors.yaml
> +++ b/Documentation/devicetree/bindings/iio/st,st-sensors.yaml
> @@ -126,6 +126,24 @@ properties:
>    mount-matrix:
>      description: an optional 3x3 mounting rotation matrix.
>  
> +  st,fullscale-mg:

I'd be inclined to say that this should spell out milligauss, but
this seems reasonable enough to me.
Acked-by: Conor Dooley <conor.dooley@microchip.com>
pw-bot: not-applicable

> +    description: |
> +      Selects the initial sensor full-scale at probe time, expressed in
> +      milligauss for magnetometers (or analogous engineering units for
> +      other sensor families that may grow this property in the future).
> +      The value must match one of the sensor-specific full-scale ranges
> +      supported by the chip; if the chip does not support the requested
> +      range the driver falls back to its built-in default.
> +
> +      This is intended for boards where the magnetometer chip picks up
> +      enough DC bias from nearby PCB structures (power planes, ferrous
> +      shields, etc.) that the kernel's chip-default highest-sensitivity
> +      range saturates one or more axes to the chip's overflow sentinel,
> +      and userspace observes that axis as permanently stuck. Declaring
> +      a wider initial range avoids the saturation at the cost of a
> +      slightly coarser quantisation.
> +    $ref: /schemas/types.yaml#/definitions/uint32
> +
>  allOf:
>    - if:
>        properties:
> -- 
> 2.43.0
> 

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