linux-kernel - Re: [PATCH v2 1/4] PCI: rockchip: limit RK3399 to 2.5 GT/s to prevent damage

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Message-ID: <CAEsQvctSY7-RQEQF2TmJU2qKPZOe9TC5g-7Jat0LQKRHYz_6dQ@mail.gmail.com>
Date: Wed, 24 Dec 2025 02:38:40 -0300
From: Geraldo Nascimento <geraldogabriel@...il.com>
To: Anand Moon <linux.amoon@...il.com>
Cc: Shawn Lin <shawn.lin@...k-chips.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>, Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor Dooley <conor+dt@...nel.org>, 
	Johan Jonker <jbx6244@...il.com>, Dragan Simic <dsimic@...jaro.org>, 
	linux-rockchip@...ts.infradead.org, linux-pci@...r.kernel.org, 
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org, 
	devicetree@...r.kernel.org
Subject: Re: [PATCH v2 1/4] PCI: rockchip: limit RK3399 to 2.5 GT/s to prevent damage

On Wed, Dec 24, 2025 at 2:18 AM Anand Moon <linux.amoon@...il.com> wrote:
>
> Hi Geraldo,
>
> On Tue, 18 Nov 2025 at 03:17, Geraldo Nascimento
> <geraldogabriel@...il.com> wrote:
> >
> > Shawn Lin from Rockchip has reiterated that there may be danger in using
> > their PCIe with 5.0 GT/s speeds. Warn the user if they make a DT change
> > from the default and drive at 2.5 GT/s only, even if the DT
> > max-link-speed property is invalid or inexistent.
> >
> > This change is corroborated by RK3399 official datasheet [1], which
> > says maximum link speed for this platform is 2.5 GT/s.
> >
> > [1] https://opensource.rock-chips.com/images/d/d7/Rockchip_RK3399_Datasheet_V2.1-20200323.pdf
> >
> To accurately determine the operating speed, we can leverage the
> PCIE_CLIENT_BASIC_STATUS0/1 fields.
> This provides a dynamic mechanism to resolve the issue.
>
> [1] https://github.com/torvalds/linux/blob/master/drivers/pci/controller/pcie-rockchip-ep.c#L533-L595
>
> Thanks
> -Anand

Hi Anand,

not to put you down but I think your approach adds unnecessary complexity.

All I care really is that the Kernel Project isn't blamed in the
future if someone happens to lose their data.

Thanks,
Geraldo Nascimento