linux-kernel - Re: [PATCH 2/3] PCI: rockchip-host: comment danger of 5.0 GT/s speed

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Message-ID: <aRhNIcGcQKp2ylqN@geday>
Date: Sat, 15 Nov 2025 06:51:29 -0300
From: Geraldo Nascimento <geraldogabriel@...il.com>
To: Dragan Simic <dsimic@...jaro.org>
Cc: linux-rockchip@...ts.infradead.org,
	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>, 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>
Subject: Re: [PATCH 2/3] PCI: rockchip-host: comment danger of 5.0 GT/s speed

On Sat, Nov 15, 2025 at 10:30:49AM +0100, Dragan Simic wrote:
> Hello Geraldo,
> 
> On Saturday, November 15, 2025 10:10 CET, Geraldo Nascimento <geraldogabriel@...il.com> wrote:
> > According to Rockchip sources, there is grave danger in enabling 5.0
> > GT/s speed for this core. Add a comment documenting that danger and
> > discouraging end-users from forcing higher speed through DT changes.
> > 
> > Link: https://lore.kernel.org/all/ffd05070-9879-4468-94e3-b88968b4c21b@rock-chips.com/
> > Reported-by: Shawn Lin <shawn.lin@...k-chips.com>
> > Signed-off-by: Geraldo Nascimento <geraldogabriel@...il.com>
> > ---
> >  drivers/pci/controller/pcie-rockchip-host.c | 5 +++++
> >  1 file changed, 5 insertions(+)
> > 
> > diff --git a/drivers/pci/controller/pcie-rockchip-host.c b/drivers/pci/controller/pcie-rockchip-host.c
> > index ee1822ca01db..7e6ff76466b7 100644
> > --- a/drivers/pci/controller/pcie-rockchip-host.c
> > +++ b/drivers/pci/controller/pcie-rockchip-host.c
> > @@ -332,6 +332,11 @@ static int rockchip_pcie_host_init_port(struct rockchip_pcie *rockchip)
> >  		/*
> >  		 * Enable retrain for gen2. This should be configured only after
> >  		 * gen1 finished.
> > +		 *
> > +		 * According to Rockchip this path is dangerous and may lead to
> > +		 * catastrophic failure. Even if the odds are small, users are
> > +		 * still discouraged to engage the corresponding DT option.
> > +		 *
> >  		 */
> >  		status = rockchip_pcie_read(rockchip, PCIE_RC_CONFIG_CR + PCI_EXP_LNKCTL2);
> >  		status &= ~PCI_EXP_LNKCTL2_TLS;
> 
> Looking good to me, thanks for this patch!  There's no need
> to emit warnings here, because they'd be emitted already in
> the rockchip_pcie_parse_dt() function.
> 
> Please feel free to include
> 
> Reviewed-by: Dragan Simic <dsimic@...jaro.org>
>

I disagree, I think the comment stands.

Even if we reduce to one line, ex:

+ May cause damage

Regards,
Geraldo Nascimento