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

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Message-ID: <aTHzYq5L7kvAPrjQ@shell.armlinux.org.uk>
Date: Thu, 4 Dec 2025 20:47:30 +0000
From: "Russell King (Oracle)" <linux@...linux.org.uk>
To: Krzysztof Kozlowski <krzk@...nel.org>
Cc: Vladimir Oltean <olteanv@...il.com>,
	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 Thu, Dec 04, 2025 at 06:32:23PM +0100, Krzysztof Kozlowski wrote:
> On 04/12/2025 18:23, Krzysztof Kozlowski wrote:
> > 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.
> 
> Although transistor would be still needed, so indeed that's still a bit
> more than a wire and resistor as I implied.
> 
> It looks like:
> https://www.electronics-tutorials.ws/wp-content/uploads/2018/05/logic-log47.gif

A bit more than even that... I do hope folk don't use exactly that,
that's the kind of thing that would be used in "learning about
electronics" projects! That's a recipe to drive a transistor into
full saturation, which makes it comparitively very slow to turn off.

-- 
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