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

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Message-ID: <20251204160247.yz42mnxvzhxas5jc@skbuf>
Date: Thu, 4 Dec 2025 18:02:47 +0200
From: Vladimir Oltean <olteanv@...il.com>
To: Krzysztof Kozlowski <krzk@...nel.org>
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 Thu, Dec 04, 2025 at 03:49:52PM +0100, Krzysztof Kozlowski wrote:
> On 04/12/2025 14:16, Vladimir Oltean wrote:
> > I get the feeling that we're complicating a simple solution because of a
> > theoretical "what if" scenario. The "NOT" gate is somewhat contrived
> 
> You downplay this case and suggest (if I get it right) that NOT gate is
> something unusual.
> 
>  I mentioned "line inverter" but it's not about NOT gate. There is no
> need for NOT gate at all, like some magical component which no one puts
> to the board. The only thing needed is just to pull the GPIO up or down,
> that's it. It's completely normal design thus it CAN happen.
> 
> Of course "can" does not mean it actually does, because certain
> configurations like powerdown-fail-safe are more likely and I am not an
> electric circuit designer to tell which one is better, but that
> downplaying does not help here.

I don't want to dismiss this comment, but I don't really understand it.
What do you mean by "line inverter", is it the component inside the GPIO
pin which makes it active low?

I thought that the premise of this patch set is that old device trees
are all (incorrectly) defined as GPIO_ACTIVE_HIGH, but someone familiar
with the matter needs to fact-check this statement.

Anyway, you and Andrew are talking about different things, you haven't
made it clear (or at least it wasn't clear to me) that the inverter you
are talking about isn't his NOT gate (that isn't described in the device
tree at all, as opposed to your inverter which would make the GPIO line
GPIO_ACTIVE_LOW - that's something verifiable).

> Just to clarify: I expect clear communication that some users will be
> broken with as good as you can provide analysis of the impact (which
> users). I only object the clame here "no one can ever pull down a GPIO
> line thus I handled all possible cases and made it backward compatible".
> 
> And that claim to quote was:
> "Therefore, regardless of whether a DTS is old or new, correct or
> incorrect, the driver now generates the correct electrical reset pulse."
> 
> which is 100% false and I am surprised how one could claim that.

Agree, the communication should be better.