linux-kernel - Re: [PATCH 1/2] dt-bindings: pinctrl: renesas,r9a09g077: Document pin configuration properties

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Message-ID: <9c1b12fb-2c30-4610-8262-5c615e1ac982@kernel.org>
Date: Fri, 16 Jan 2026 15:28:33 +0100
From: Krzysztof Kozlowski <krzk@...nel.org>
To: "Lad, Prabhakar" <prabhakar.csengg@...il.com>,
 Conor Dooley <conor@...nel.org>, Linus Walleij <linus.walleij@...aro.org>,
 Geert Uytterhoeven <geert+renesas@...der.be>
Cc: Rob Herring <robh@...nel.org>, Krzysztof Kozlowski <krzk+dt@...nel.org>,
 Conor Dooley <conor+dt@...nel.org>, Magnus Damm <magnus.damm@...il.com>,
 linux-renesas-soc@...r.kernel.org, linux-gpio@...r.kernel.org,
 devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
 Biju Das <biju.das.jz@...renesas.com>,
 Fabrizio Castro <fabrizio.castro.jz@...esas.com>,
 Lad Prabhakar <prabhakar.mahadev-lad.rj@...renesas.com>
Subject: Re: [PATCH 1/2] dt-bindings: pinctrl: renesas,r9a09g077: Document pin
 configuration properties

On 14/01/2026 21:53, Lad, Prabhakar wrote:
>>>>> What are the meanings of "0" and "1" for slew rate? Why isn't this given
>>>> I'll add a description for it (0 = slow, 1 = fast) and the same values
>>>> are programmed in the register to configure the slew rate.
>>>>
>>>>> as the actual rates? The docs surely give more detail than just "slow"
>>>>> and "fast".
>>>> You mean to represent slew-rate in some sort of a unit?
>>>>
>>> Based on the comments from the HW team, there is no numerical
>>> definition to represent slow/fast It only defines a relative
>>> relationship.
>>>>>
>>>>>> +      renesas,drive-strength:
>>>>>> +        description:
>>>>>> +          Drive strength configuration value. Valid values are 0 to 3, representing
>>>>>> +          increasing drive strength from low, medium, high and ultra high.
>>>>>
> I got the feedback from the HW team "The RZ/T2H drive strength
> (driving ability) is expressed using abstract levels such as Low,
> Middle, and High. These values do not correspond directly to specific

Hold my beer and let me design PCB... I will use high voltage power
supply, then small resistor and small capacitor. Ah, and that regulator
here should operate on medium/middle voltage. Looks about right, all
ready to send to fab!

> mA units. To determine how much current the pin can actually drive,
> the engineer must refer to the electrical characteristics table.
> Therefore, the drive strength in RZ/T2H is a parameter that switches
> the internal output transistor mode rather than directly representing
> a physical drive current.
> Consequently, expressing RZ/T2H drive strength in milli- or
> micro-amps, as suggested by the reviewer, is inappropriate. To
> accurately reflect the SoC's hardware specification, introducing a
> custom property is essential."

So the hardware team tells you how you should model DT - "introducing a
custom property is essential".

That's pretty bold statement and very poor language construct. It is not
hardware team which decides how DT should be written.


Best regards,
Krzysztof