linux-kernel - Re: [PATCH v2 1/2] hwmon:(pmbus/tda38740a) TDA38740A Voltage Regulator Driver

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Message-ID: <787ffcff-28cb-43e0-97db-19dd7a996d13@roeck-us.net>
Date: Sun, 1 Feb 2026 16:29:38 -0800
From: Guenter Roeck <linux@...ck-us.net>
To: ashish yadav <ashishyadav78@...il.com>
Cc: Rob Herring <robh@...nel.org>, Krzysztof Kozlowski <krzk+dt@...nel.org>,
 Conor Dooley <conor+dt@...nel.org>, linux-hwmon@...r.kernel.org,
 devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
 ASHISH YADAV <Ashish.Yadav@...ineon.com>
Subject: Re: [PATCH v2 1/2] hwmon:(pmbus/tda38740a) TDA38740A Voltage
 Regulator Driver

On 1/22/26 03:42, ashish yadav wrote:
> Hi Guenter,
> 
> Please find my response inline.
> 
> Thanks & Regards
>     Ashish Yadav
> 
> On Tue, Jan 13, 2026 at 8:40 PM Guenter Roeck <linux@...ck-us.net> wrote:
>>
>> On 1/12/26 23:24, ashish yadav wrote:
>>
>>>> The need for this, especially why it would only be needed for PMBUS_READ_VOUT
>>>> but not for any other VOUT related commands, is still insufficiently explained
>>>> (and I failed to understand the rationale provided earlier).
>>>>
>>>
>>> It is specifically needed for READ_VOUT as it is being used by
>>> external controller to monitor the rail health.
>>> Other Vout related parameters are used internally in the IC to for
>>> output voltage related protections and does not impact any external
>>> decision making.
>>>
>>
>> Sorry, that doesn't really make sense. How would the chip know to match
>> VOUT with its VOUT limits if both don't use the same scale ?
>>
> The chip telemetry would still show Vout as 0.7V as it does not know
> about the external feedback resistors.
> Hence, no need to scale internal Vout related parameters.
> This scale is only for external vendor use to tweak their telemetry
> output voltage reading.
> 

You fail to explain why VOUT_SCALE_LOOP - which is supposed to handle such
situations - can not be used, and why it would be acceptable for other VOUT
related attributes such as VOUT_MIN, VOUT_MAX, VOUT_MARGIN_LOW, VOUT_MARGIN_HIGH,
and the various VOUT fault limits to show the wrong values.

For reference:

VOUT_SCALE_LOOP:
"Used to account for any external attenuation network on VOUT sense
  feedback and provide correct VOUT reporting."

Guenter