linux-kernel - Re: [PATCH v2 1/2] ARM64: dts: mediatek: fix MT7531 reset GPIO polarity on multiple boards

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Message-ID: <52d3469e-104e-4950-802a-2b83cea8d726@lunn.ch>
Date: Thu, 20 Nov 2025 23:08:05 +0100
From: Andrew Lunn <andrew@...n.ch>
To: Chen Minqiang <ptpt52@...il.com>
Cc: 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>,
	Daniel Golle <daniel@...rotopia.org>,
	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 v2 1/2] ARM64: dts: mediatek: fix MT7531 reset GPIO
 polarity on multiple boards

On Fri, Nov 21, 2025 at 05:38:04AM +0800, Chen Minqiang wrote:
> The MT7531 reset pin is active-low, but several DTS files configured the
> reset-gpios property without GPIO_ACTIVE_LOW. This causes the reset GPIO
> to behave as active-high and prevents the switch from being properly reset.
> 
> Update all affected DTS files to correctly use GPIO_ACTIVE_LOW so that
> the reset polarity matches the hardware design.
> 
> Boards fixed:
>  - mt7622-bananapi-bpi-r64
>  - mt7622-rfb1
>  - mt7986a-bananapi-bpi-r3
>  - mt7986a-rfb
>  - mt7986b-rfb
> 
> Note: the previous DTS description used the wrong polarity but the
> driver also assumed the opposite polarity, resulting in a matched pair
> of bugs that worked together. Updating the DTS requires updating the
> driver at the same time; old kernels will not reset the switch correctly
> when used with this DTS.

Sometimes we need to live with issues like this, because of:

> Compatibility
> -------------
> 
> Correcting the polarity creates intentional incompatibility:
> 
>  * New kernel + old DTS:
>    The driver now expects active-low, but out-of-tree DTS still marks
>    active-high, causing the reset sequence to invert.
> 
>  * Old kernel + new DTS:
>    The old driver toggles reset assuming active-high, which now
>    conflicts with the corrected active-low DTS.
> 
> This was unavoidable because the original DTS was factually wrong.
> Out-of-tree DTS users must update their DTS together with the kernel.

So the real question is, does this actually harm anything? Do we see
any real issues?

	Andrew