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Date: Thu, 2 May 2024 07:31:15 +0700
From: Bagas Sanjaya <bagasdotme@gmail.com>
To: =?utf-8?Q?Jo=C3=A3o_Paulo_Gon=C3=A7alves?= <jpaulo.silvagoncalves@gmail.com>,
	Linux IIO <linux-iio@vger.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	Linux Devicetree <devicetree@vger.kernel.org>
Cc: joao.goncalves@toradex.com, Rob Herring <robh@kernel.org>,
	Krzysztof Kozlowski <krzk+dt@kernel.org>,
	Conor Dooley <conor+dt@kernel.org>,
	Jonathan Cameron <jic23@kernel.org>,
	Lars-Peter Clausen <lars@metafoo.de>
Subject: Re: Supporting a Device with Switchable Current/Voltage Measurement
Message-ID: <ZjLe0yIpMyPRl-eZ@archie.me>
References: <20240501233853.32y4ev7jvas5ahdz@joaog-nb>
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[also Cc: IIO and devicetree maintainers]

On Wed, May 01, 2024 at 08:38:53PM -0300, Jo=C3=A3o Paulo Gon=C3=A7alves wr=
ote:
> Hello all,
>=20
> We need to support a hardware that can measure current and voltage on
> the same differential analog input, similar to a multimeter. The mode
> of measurement is controlled by a GPIO switch and goes to different
> ADC inputs depending on the mode. If the switch is enabled, a current
> loop with a shunt is enabled for current measurement; otherwise, voltage
> is measured. From the software point of view, we are considering using
> the iio-rescale driver as a consumer of an ADC IIO parent device. One
> of the problems is that we need to change the mode of measurement at
> runtime, but we are trying to avoid using some userspace "hack". The
> other is that for a minimal solution to enable the mode from boot, we
> can use a gpio-hog and control it with overlays. However,
> still would be better that this was done by the kernel. Do you know
> or have some guidance on how to properly support this in the kernel?
>=20
> For the in kernel gpio solution, this is a draft of DT we are thinking:
>=20
> current-sense {
>       compatible =3D "current-sense-shunt";
>       io-channels =3D <&adc 0>;
>       gpio =3D <&main_gpio0 29 GPIO_ACTIVE_HIGH>;
>       shunt-resistor-micro-ohms =3D <3300000>;     =20
> };
>=20
> voltage-sense {
>         compatible =3D "voltage-divider";
>         io-channels =3D <&adc 1>;
>         gpio =3D <&main_gpio0 29 GPIO_ACTIVE_LOW>;
>         output-ohms =3D <22>;
>         full-ohms =3D <222>;
> };

What are these ohms and where do you get them?

Confused...

--=20
An old man doll... just what I always wanted! - Clara

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