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

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Message-ID: <20240502145228.qgocejdzjaaxt2zq@joaog-nb>
Date: Thu, 2 May 2024 11:53:04 -0300
From: jpaulo.silvagoncalves@...il.com
To: Jonathan Cameron <Jonathan.Cameron@...wei.com>,
	Peter Rosin <peda@...ntia.se>
Cc: João Paulo Gonçalves <jpaulo.silvagoncalves@...il.com>,
	linux-iio@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: Supporting a Device with Switchable Current/Voltage Measurement

On Thu, May 02, 2024 at 01:36:23PM +0100, Jonathan Cameron wrote:
> Superficially sounds like you want a mixture of appropriate analog front ends
> and a Mux.  I haven't tried the combination but it should be possible to do
> something like this with 
> 
> An IIO mux via this binding
> https://elixir.bootlin.com/linux/v6.9-rc6/source/Documentation/devicetree/bindings/iio/multiplexer/io-channel-mux.yaml
> (that includes a gpio-mux example).
> 
> Consumed in turn by a pair of AFE devices.
> 
> Then you should be able to just read from which ever of the AFE device you want.
> A sysfs read from
> /sys/bus/iio/devices/iio\:deviceA/in_voltage_raw
> will switch the mux to appropriate place then request the
> voltage from the iio-mux, which in turn requests it from the ADC IIO driver.
> 
> /sys/bus/iio/devices/iio\:deviceB/in_current_raw
> switches the mux the other way and otherwise the flow as above.
> 
> Jonathan
> 

On Thu, May 02, 2024 at 03:49:03PM +0200, Peter Rosin wrote:
> I just realized that it's also possible to do this "the other way around". Maybe
> that makes more sense?
> 
> Cheers,
> Peter
> 
> mux: gpio-mux {
> 	compatible = "gpio-mux";
> 	#mux-control-cells = <0>;
> 
> 	gpios-mux = <&main_gpio0 29 GPIO_ACTIVE_HIGH>;
> };
> 
> rcs: raw-current-sense {
> 	compatible = "io-channel-mux";
> 	io-channels = <&adc 0>;
> 	io-channel-names = "parent";
> 	#io-channel-cells = <1>;
> 
> 	mux-controls = <&mux>;
> 
> 	channels = "raw-current", "";
> };
> 
> rvs: raw-voltage-sense {
> 	compatible = "io-channel-mux";
> 	io-channels = <&adc 1>;
> 	io-channel-names = "parent";
> 	#io-channel-cells = <1>;
> 
> 	mux-controls = <&mux>;
> 
> 	channels = "", "raw-voltage";
> };
> 
> current-sense {
> 	compatible = "current-sense-shunt";
> 	io-channels = <&rcs 0>;
> 	io-channel-name = "current";
> 
> 	shunt-resistor-micro-ohms = <3300000>;
> };
> 
> voltage-sense {
> 	compatible = "voltage-divider";
> 	io-channels = <&rvs 1>;
> 	io-channel-name = "voltage";
> 
> 	output-ohms = <22>;
> 	full-ohms = <222>;
> };
> 
> Cheers,
> Peter

A lot of good information. I didn't know about the iio-mux. It might 
solve our problem, and I will do some testing with it.

Thanks a lot for the help! 

Regards,
João Paulo Gonçalves