linux-kernel - Re: [PATCH] arm64: dts: rockchip: align bindings to PCIe spec

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Message-ID: <aQ1c7ZDycxiOIy8Y@geday>
Date: Thu, 6 Nov 2025 23:43:57 -0300
From: Geraldo Nascimento <geraldogabriel@...il.com>
To: Shawn Lin <shawn.lin@...k-chips.com>
Cc: Lorenzo Pieralisi <lpieralisi@...nel.org>,
	Krzysztof Wilczyński <kwilczynski@...nel.org>,
	Manivannan Sadhasivam <mani@...nel.org>,
	Rob Herring <robh@...nel.org>, Bjorn Helgaas <bhelgaas@...gle.com>,
	Heiko Stuebner <heiko@...ech.de>, linux-pci@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	devicetree@...r.kernel.org,
	Krzysztof Kozlowski <krzk+dt@...nel.org>,
	Conor Dooley <conor+dt@...nel.org>,
	Johan Jonker <jbx6244@...il.com>,
	linux-rockchip@...ts.infradead.org
Subject: Re: [PATCH] arm64: dts: rockchip: align bindings to PCIe spec

On Wed, Nov 05, 2025 at 04:56:36PM +0800, Shawn Lin wrote:
> 在 2025/11/05 星期三 16:18, Geraldo Nascimento 写道:
> > Hi Shawn, glad to hear from you.
> > 
> > Perhaps the following change is better? It resolves the issue
> > without the added complication of open drain. After you questioned
> > if open drain is actually part of the spec, I remembered that
> > GPIO_OPEN_DRAIN is actually (GPIO_SINGLE_ENDED | GPIO_LINE_OPEN_DRAIN)
> > so I decided to test with just GPIO_SINGLE_ENDED and it works.

Shawn,

I quote from the PCIe Mini Card Electromechanical Specification Rev 1.2

"3.4.1. Logic Signal Requirements

The 3.3V card logic levels for single-ended digital signals (WAKE#,
CLKREQ#, PERST#, and W_DISABLE#) are given in Table 3-7. [...]"

So while you are correct that PERST# is most definitely not Open Drain,
there's evidence on the spec that defines this signal as Single-Ended.

Thanks,
Geraldo Nascimento