linux-kernel - Re: [PATCH 0/3] PCI: rockchip: 5.0 GT/s speed may be dangerous

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Message-ID: <257951b7-c22e-9707-6aba-3dc5794306bb@manjaro.org>
Date: Mon, 17 Nov 2025 04:57:11 +0100
From: "Dragan Simic" <dsimic@...jaro.org>
To: "Shawn Lin" <shawn.lin@...k-chips.com>
Cc: "Geraldo Nascimento" <geraldogabriel@...il.com>, "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 0/3] PCI: rockchip: 5.0 GT/s speed may be dangerous

Hello Shawn and Geraldo,

On Monday, November 17, 2025 04:42 CET, Shawn Lin <shawn.lin@...k-chips.com> wrote:
> 在 2025/11/15 星期六 17:10, Geraldo Nascimento 写道:
> > In recent interactions with Shawn Lin from Rockchip it came to my
> > attention there's an unknown errata regarding 5.0 GT/s operational
> > speed of their PCIe core. According to Shawn there's grave danger
> > even if the odds are low. To contain any damage, let's cover the
> > remaining corner-cases where the default would lead to 5.0 GT/s
> > operation as well as add a comment to Root Complex driver core,
> > documenting this danger.
> 
> I'm not sure just adding a warn would be a good choice. Could we totally
> force to use gen1 and add a warn if trying to use Gen2.

I think that forcing 2.5 GT/s with an appropriate warning message
is a good idea.  That would be like some quirk that gets applied
automatically, to prevent data corruption, while warning people
who attempt to "overclock" the PCIe interface.

> Meanwhile amend the commit message to add a reference
> of RK3399 official datesheet[1] which says PCIe on RK3399 should only
> support 2.5GT/s?
> 
> [1]https://opensource.rock-chips.com/images/d/d7/Rockchip_RK3399_Datasheet_V2.1-20200323.pdf

Also, rewording the patch summary as follows below may be good,
because that would provide more details:

  PCI: rockchip: Warn about Gen2 5.0 GT/s on RK3399 being unsafe

Or, if we'll go with the automatic downgrading, like this:

  PCI: rockchip: Limit RK3399 to Gen1 2.5 GT/s to prevent breakage