linux-kernel - Re: [PATCH v4 1/2] dt-bindings: hwmon: ti,ina2xx: Add INA233 device

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Message-ID: <CAAfUjZGSgdQYwC24S__EO13-q1HQWVkUP7oDgJm-=AeeXgr1DQ@mail.gmail.com>
Date: Thu, 16 Jan 2025 21:52:08 +0800
From: Leo Yang <leo.yang.sy0@...il.com>
To: Krzysztof Kozlowski <krzk@...nel.org>
Cc: jdelvare@...e.com, linux@...ck-us.net, robh@...nel.org, krzk+dt@...nel.org, 
	conor+dt@...nel.org, Leo-Yang@...ntatw.com, corbet@....net, 
	Delphine_CC_Chiu@...ynn.com, linux-hwmon@...r.kernel.org, 
	devicetree@...r.kernel.org, linux-kernel@...r.kernel.org, 
	linux-doc@...r.kernel.org
Subject: Re: [PATCH v4 1/2] dt-bindings: hwmon: ti,ina2xx: Add INA233 device

Hi Krzysztof,

On Thu, Jan 16, 2025 at 6:47 PM Krzysztof Kozlowski <krzk@...nel.org> wrote:
>
> > +      This value will be used to calculate the Current_LSB and current/power
> > +      coefficient for the pmbus and to calibrate the IC.
> > +    minimum: 32768
> > +    maximum: 4294967295
>
> Uh, are these real values measurable by the device? The last one looks
> like UINT_MAX.

According to the spec I don't see a definition of the upper limit of the
current measurement, it all depends on how low the shunt resistance can
be, so I'll use the upper limit of the u32 as the maximum for now, even
though it's unlikely that this number will be present in the actual circuit.

>
> > +    default: 32768000
>
> Default is 32 A? For what applications is this sensor used?
>

According to spec 8.2.2.1 Programming the Calibration Register example,
a Current_LSB with a maximum expected current of 15A is approximately
457.7uA.
The example shows that a Current_LSB of 500 or 1000uA/bit can be used.
So I choose 1000uA as the default value here, this value corresponds to
the expected maximum current which is 32A (with some loss of accuracy to
 have a larger measurement range), and yes maybe the user doesn't
need such a large current, so the accuracy-sensitive use of the scene
can be adjusted according to the actual measurement range of the
expected maximum current, I'm trying to retain some flexibility for the
user.

Thank you for all your suggestions, they are very useful and
I have gained a lot from them.

Best Regards,

Leo Yang