linux-kernel - Re: [PATCH] hwmon: ina238: Add support for shunt voltage scaling

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Message-ID: <CAGfYmwX2fEPmLbc2rP=R10WaV_LpX-_uy+SZnJ+gYg3bnO_Yag@mail.gmail.com>
Date: Tue, 21 Jan 2025 09:18:54 +0800
From: Potin Lai <potin.lai.pt@...il.com>
To: Guenter Roeck <linux@...ck-us.net>
Cc: Jean Delvare <jdelvare@...e.com>, Patrick Williams <patrick@...cx.xyz>, linux-hwmon@...r.kernel.org, 
	linux-kernel@...r.kernel.org, Cosmo Chou <cosmo.chou@...ntatw.com>, 
	Potin Lai <potin.lai@...ntatw.com>
Subject: Re: [PATCH] hwmon: ina238: Add support for shunt voltage scaling

On Tue, Jan 21, 2025 at 12:38 AM Guenter Roeck <linux@...ck-us.net> wrote:
>
> On 1/20/25 08:23, Potin Lai wrote:
> > The INA238 sensor reports shunt voltage with microvolt precision.
> > However, the hwmon driver currently exposes this value only in
> > millivolts via `in0_input`, which results in a loss of precision for
> > readings within the range of ±1 mV.
> >
> > This patch introduces an `in0_scale` attribute to provide the scaling
> > factor applied to the shunt voltage reading. By exposing this attribute,
> > users can accurately interpret the in0_input values in microvolts,
> > preserving the sensor's full precision.
> >
> > Signed-off-by: Potin Lai <potin.lai.pt@...il.com>
>
> Sorry, this is an ABI violation and thus a no-go. in0_input is and will
> always be reported in mV.
>
> Guenter
>

Hi Guenter,
In our use case, the shunt voltage is less than 1 mv most of the time.
I would like to get your advice on the correct way of getting
microvolt reading from the driver? Thank you.

Best regards,
Potin