Re: [PATCH 1/3] PCI: rockchip: warn of danger of 5.0 GT/s speeds

From: Geraldo Nascimento <geraldogabriel@gmail.com>
To: Dragan Simic <dsimic@manjaro.org>
Cc: linux-rockchip@lists.infradead.org,
	"Shawn Lin" <shawn.lin@rock-chips.com>,
	"Lorenzo Pieralisi" <lpieralisi@kernel.org>,
	"Krzysztof Wilczyński" <kwilczynski@kernel.org>,
	"Manivannan Sadhasivam" <mani@kernel.org>,
	"Rob Herring" <robh@kernel.org>,
	"Bjorn Helgaas" <bhelgaas@google.com>,
	"Heiko Stuebner" <heiko@sntech.de>,
	linux-pci@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
	linux-kernel@vger.kernel.org, devicetree@vger.kernel.org,
	"Krzysztof Kozlowski" <krzk+dt@kernel.org>,
	"Conor Dooley" <conor+dt@kernel.org>,
	"Johan Jonker" <jbx6244@gmail.com>
Subject: Re: [PATCH 1/3] PCI: rockchip: warn of danger of 5.0 GT/s speeds
Date: Sat, 15 Nov 2025 06:49:33 -0300	[thread overview]
Message-ID: <aRhMrXz_RlL0WErZ@geday> (raw)
In-Reply-To: <a214ac9a-36d9-6505-64a8-92af2da42cf1@manjaro.org>

On Sat, Nov 15, 2025 at 10:24:49AM +0100, Dragan Simic wrote:
> Hello Geraldo,
> 
> On Saturday, November 15, 2025 10:10 CET, Geraldo Nascimento <geraldogabriel@gmail.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 at the same time, drive at 2.5 GT/s only, in case
> > the DT max-link-speed property is invalid or inexistent.
> > 
> > Fixes: 956cd99b35a8 ("PCI: rockchip: Separate common code from RC driver")
> > Link: https://lore.kernel.org/all/ffd05070-9879-4468-94e3-b88968b4c21b@rock-chips.com/
> > Reported-by: Shawn Lin <shawn.lin@rock-chips.com>
> > Signed-off-by: Geraldo Nascimento <geraldogabriel@gmail.com>
> > ---
> >  drivers/pci/controller/pcie-rockchip.c | 8 ++++++--
> >  1 file changed, 6 insertions(+), 2 deletions(-)
> > 
> > diff --git a/drivers/pci/controller/pcie-rockchip.c b/drivers/pci/controller/pcie-rockchip.c
> > index 0f88da378805..ed67886a6d43 100644
> > --- a/drivers/pci/controller/pcie-rockchip.c
> > +++ b/drivers/pci/controller/pcie-rockchip.c
> > @@ -66,8 +66,12 @@ 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)
> > +		dev_warn(dev, "5.0 GT/s may lead to catastrophic failure\n");
> >  
> >  	for (i = 0; i < ROCKCHIP_NUM_PM_RSTS; i++)
> >  		rockchip->pm_rsts[i].id = rockchip_pci_pm_rsts[i];
> 
> Looking good to me, thanks for this patch!  People often declare
> PCIe Gen2 on RK3399-based boards as "works for me", which actually
> happens very often, but such simple evaluations cannot be taken
> as a proof of Gen2 correctness.
> 
> Furthermore, RK3399's internal interconnects limit the effective
> I/O speed of PCIe transfers already, so switching to PCIe Gen1
> actually doesn't result in some large I/O performance penalties.
> 
> With all that in mind, please feel free to include
> 
> Reviewed-by: Dragan Simic <dsimic@manjaro.org>

Hi Dragan,

I think I'll include a Reported-By: you too, since you were the first to
warn me of unknown errata regarding Rockchip PCIe.

I told you it was a test of mine but I didn't realize the grave danger
implied by Shawn Lin declarations.

Once I realized this could end badly the only way I could retribute was
to send a few corrections :)

Thank you,
Geraldo Nascimento