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: <qncj72c3owrw7rvnj6jit2sbn4ojyr3kztcjailfxtdboan6sy@ddh5g7v4fcvt>
Date: Thu, 18 Dec 2025 13:35:37 +0530
From: Manivannan Sadhasivam <mani@...nel.org>
To: Geraldo Nascimento <geraldogabriel@...il.com>
Cc: Shawn Lin <shawn.lin@...k-chips.com>, 
	Lorenzo Pieralisi <lpieralisi@...nel.org>, Krzysztof Wilczyński <kwilczynski@...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 Mon, Nov 17, 2025 at 06:47:05PM -0300, Geraldo Nascimento 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
> 
> Fixes: 956cd99b35a8 ("PCI: rockchip: Separate common code from RC driver")
> Link: https://lore.kernel.org/all/ffd05070-9879-4468-94e3-b88968b4c21b@rock-chips.com/
> Cc: stable@...r.kernel.org
> Reported-by: Dragan Simic <dsimic@...jaro.org>
> Reported-by: Shawn Lin <shawn.lin@...k-chips.com>
> Reviewed-by: Dragan Simic <dsimic@...jaro.org>
> Signed-off-by: Geraldo Nascimento <geraldogabriel@...il.com>
> ---
>  drivers/pci/controller/pcie-rockchip.c | 10 ++++++++--
>  1 file changed, 8 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/pci/controller/pcie-rockchip.c b/drivers/pci/controller/pcie-rockchip.c
> index 0f88da378805..992ccf4b139e 100644
> --- a/drivers/pci/controller/pcie-rockchip.c
> +++ b/drivers/pci/controller/pcie-rockchip.c
> @@ -66,8 +66,14 @@ int rockchip_pcie_parse_dt(struct rockchip_pcie *rockchip)
>  	}
>  
>  	rockchip->link_gen = of_pci_get_max_link_speed(node);
> -	if (rockchip->link_gen < 0 || rockchip->link_gen > 2)
> -		rockchip->link_gen = 2;
> +	if (rockchip->link_gen < 0 || rockchip->link_gen > 2) {
> +		rockchip->link_gen = 1;
> +		dev_warn(dev, "invalid max-link-speed, set to 2.5 GT/s\n");
> +	}
> +	else if (rockchip->link_gen == 2) {
> +		rockchip->link_gen = 1;
> +		dev_warn(dev, "5.0 GT/s is dangerous, set to 2.5 GT/s\n");

What does 'danger' really mean here? Link instability or something else?

Error messages should be precise and not fearmongering.

- Mani

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