linux-kernel - Re: Supporting a Device with Switchable Current/Voltage Measurement

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Message-ID: <ZjLe0yIpMyPRl-eZ@archie.me>
Date: Thu, 2 May 2024 07:31:15 +0700
From: Bagas Sanjaya <bagasdotme@...il.com>
To: João Paulo Gonçalves <jpaulo.silvagoncalves@...il.com>,
	Linux IIO <linux-iio@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Linux Devicetree <devicetree@...r.kernel.org>
Cc: joao.goncalves@...adex.com, Rob Herring <robh@...nel.org>,
	Krzysztof Kozlowski <krzk+dt@...nel.org>,
	Conor Dooley <conor+dt@...nel.org>,
	Jonathan Cameron <jic23@...nel.org>,
	Lars-Peter Clausen <lars@...afoo.de>
Subject: Re: Supporting a Device with Switchable Current/Voltage Measurement

[also Cc: IIO and devicetree maintainers]

On Wed, May 01, 2024 at 08:38:53PM -0300, João Paulo Gonçalves wrote:
> Hello all,
> 
> 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?
> 
> For the in kernel gpio solution, this is a draft of DT we are thinking:
> 
> current-sense {
>       compatible = "current-sense-shunt";
>       io-channels = <&adc 0>;
>       gpio = <&main_gpio0 29 GPIO_ACTIVE_HIGH>;
>       shunt-resistor-micro-ohms = <3300000>;      
> };
> 
> voltage-sense {
>         compatible = "voltage-divider";
>         io-channels = <&adc 1>;
>         gpio = <&main_gpio0 29 GPIO_ACTIVE_LOW>;
>         output-ohms = <22>;
>         full-ohms = <222>;
> };

What are these ohms and where do you get them?

Confused...

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

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