linux-kernel - Re: [PATCH v3 2/2] net: dsa: mt7530: Use GPIO polarity to generate correct reset sequence

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Message-ID: <178afbeb-168f-4765-bb0b-fad0bcd29382@kernel.org>
Date: Thu, 4 Dec 2025 18:23:48 +0100
From: Krzysztof Kozlowski <krzk@...nel.org>
To: Vladimir Oltean <olteanv@...il.com>
Cc: Daniel Golle <daniel@...rotopia.org>, Frank Wunderlich <frankwu@....de>,
 Andrew Lunn <andrew@...n.ch>, Chen Minqiang <ptpt52@...il.com>,
 Rob Herring <robh@...nel.org>, Krzysztof Kozlowski <krzk+dt@...nel.org>,
 Conor Dooley <conor+dt@...nel.org>, Matthias Brugger
 <matthias.bgg@...il.com>,
 AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>,
 "Chester A. Unal" <chester.a.unal@...nc9.com>,
 DENG Qingfang <dqfext@...il.com>, Sean Wang <sean.wang@...iatek.com>,
 linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
 linux-mediatek@...ts.infradead.org, netdev@...r.kernel.org
Subject: Re: [PATCH v3 2/2] net: dsa: mt7530: Use GPIO polarity to generate
 correct reset sequence

On 04/12/2025 18:11, Vladimir Oltean wrote:
> On Thu, Dec 04, 2025 at 05:48:07PM +0100, Krzysztof Kozlowski wrote:
>> Both are the same - inverter or NOT gate, same stuff. It is just
>> connecting wire to pull up, not actual component on the board (although
>> one could make and buy such component as well...). We never describe
>> these inverters in the DTS, these are just too trivial circuits, thus
>> the final GPIO_ACTIVE_XXX should already include whatever is on the wire
>> between SoC and device.
> 
> Please read what Andrew said:
> https://lore.kernel.org/netdev/3fbc4e67-b931-421c-9d83-2214aaa2f6ed@lunn.ch/
> 
>   Assuming there is not a NOT gate placed between the GPIO and the reset
>   pin, because the board designer decided to do that for some reason?
>                    ~~~~~~~~~~~~~~
> 
> You two are *not* talking about the same thing. I dismissed the

It's the same thing. NOT gate is just pulling some pin down or up.

> probability of there being a NOT gate in the form of a discrete chip on

We do not describe NOT gates as discreet chips. I don't think anyone
actually places something as NOT gate. It's logical NOT gate, but on
circuit it is just pull up/down as I said multiple times. The pull +
resistor is the "NOT gate".

It's so easy and that's why it is potentially so common design.

> the PCB, *exactly because* you can most likely invert the signal in the
> GPIO pin itself.

Best regards,
Krzysztof