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

From: "Diederik de Haas" <diederik@cknow-tech.com>
To: "Dragan Simic" <dsimic@manjaro.org>,
	"Manivannan Sadhasivam" <mani@kernel.org>
Cc: "Geraldo Nascimento" <geraldogabriel@gmail.com>,
	"Shawn Lin" <shawn.lin@rock-chips.com>,
	"Lorenzo Pieralisi" <lpieralisi@kernel.org>,
	"Krzysztof Wilczyński" <kwilczynski@kernel.org>,
	"Rob Herring" <robh@kernel.org>,
	"Bjorn Helgaas" <bhelgaas@google.com>,
	"Heiko Stuebner" <heiko@sntech.de>,
	"Krzysztof Kozlowski" <krzk+dt@kernel.org>,
	"Conor Dooley" <conor+dt@kernel.org>,
	"Johan Jonker" <jbx6244@gmail.com>,
	linux-rockchip@lists.infradead.org, linux-pci@vger.kernel.org,
	linux-arm-kernel@lists.infradead.org,
	linux-kernel@vger.kernel.org, devicetree@vger.kernel.org
Subject: Re: [PATCH v2 1/4] PCI: rockchip: limit RK3399 to 2.5 GT/s to prevent damage
Date: Thu, 18 Dec 2025 11:01:16 +0100	[thread overview]
Message-ID: <DF197NIRHLIJ.3LIG9GJGJQLQX@cknow-tech.com> (raw)
In-Reply-To: <3ea8ac20-6332-0c0c-645b-36ca4231c109@manjaro.org>

On Thu Dec 18, 2025 at 10:47 AM CET, Dragan Simic wrote:
> Heello Manivannan and Geraldo,
>
> On Thursday, December 18, 2025 09:05 CET, Manivannan Sadhasivam <mani@kernel.org> wrote:
>> 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@vger.kernel.org
>> > Reported-by: Dragan Simic <dsimic@manjaro.org>
>> > Reported-by: Shawn Lin <shawn.lin@rock-chips.com>
>> > Reviewed-by: Dragan Simic <dsimic@manjaro.org>
>> > Signed-off-by: Geraldo Nascimento <geraldogabriel@gmail.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.
>
> I agree that the original wording is a bit suboptimal, and I'd suggest
> to Geraldo that the produced warning message is changed to
>
>   "5.0 GT/s may cause data corruption, limited to to 2.5 GT/s\n"
>
> or something similar, to better reflect the actual underlying issue.

s/limited to to/therefore limit speed to/ ?

Cheers,
  Diederik