linux-kernel - Re: [PATCH] arm64: dts: rockchip: align bindings to PCIe spec

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Message-ID: <aReSPbRxCgdNRI9y@geday>
Date: Fri, 14 Nov 2025 17:34:05 -0300
From: Geraldo Nascimento <geraldogabriel@...il.com>
To: Shawn Lin <shawn.lin@...k-chips.com>
Cc: 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 <linux-pci@...r.kernel.org>,
	linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	devicetree <devicetree@...r.kernel.org>,
	krzk+dt <krzk+dt@...nel.org>, conor+dt <conor+dt@...nel.org>,
	Johan Jonker <jbx6244@...il.com>,
	linux-rockchip <linux-rockchip@...ts.infradead.org>,
	Simon Glass <sjg@...omium.org>,
	Philipp Tomsich <philipp.tomsich@...ll.eu>,
	Kever Yang <kever.yang@...k-chips.com>,
	Tom Rini <trini@...sulko.com>, u-boot@...ts.denx.de,
	张烨 <ye.zhang@...k-chips.com>
Subject: Re: [PATCH] arm64: dts: rockchip: align bindings to PCIe spec

On Fri, Nov 14, 2025 at 05:16:21PM +0800, Shawn Lin wrote:
> Don't worry, it's helpful, so I think Ye could have a look.
> May I ask if the failure only happened to one specific board?

Hi Shawn,

Yes, testing is restricted to my Radxa Rock Pi N10 board.

> 
> Another thing I noticed is about one commit:
> 114b06ee108c ("PCI: rockchip: Set Target Link Speed to 5.0 GT/s before 
> retraining")
> 
> It said: "Rockchip controllers can support up to 5.0 GT/s link speed."
> But we issued an errata long time ago to announced it doesn't, you could
> also check the PCIe part of RK3399 datasheet:
> https://opensource.rock-chips.com/images/d/d7/Rockchip_RK3399_Datasheet_V2.1-20200323.pdf

OK, I'm partly responsible for that as author of the commit in question.

First off let me say I do not intend to send any patches setting
max-link-speed to TWO for this platform.

I understand you issued an erratum, but are you absolutely sure about
that erratum? Because my testing shows otherwise:

---
With max-link-speed = <2>
pci 0000:01:00.0: 16.000 Gb/s available PCIe bandwidth, limited by 5.0 GT/s PCIe x4 link at 0000:00:00.0 (capable of 31.504 Gb/s with 8.0 GT/s PCIe x4 link)

/dev/nvme0n1:
 Timing cached reads:   3002 MB in  2.00 seconds = 1502.21 MB/sec
 Timing buffered disk reads: 2044 MB in  3.00 seconds = 680.79 MB/sec
---
With max-link-speed = <1>
pci 0000:01:00.0: 8.000 Gb/s available PCIe bandwidth, limited by 2.5 GT/s PCIe x4 link at 0000:00:00.0 (capable of 31.504 Gb/s with 8.0 GT/s PCIe x4 link)

/dev/nvme0n1:
 Timing cached reads:   2730 MB in  2.00 seconds = 1366.15 MB/sec
 Timing buffered disk reads: 2028 MB in  3.00 seconds = 675.71 MB/sec
---

As you can see, not only the kernel PCI driver recognizes 5.0 GT/s PCIe
link but there's even a marginal increase in cached reads as measured by
hdparm, the gains are of course limited by CPU performance.

> Also we set max-link-speed to ONE in rk3399-base.dtsi but seems another
> patch slip in: 755fff528b1b ("arm64: dts: rockchip: add variables for 
> pcie completion to helios64")

I can't speak for patches I haven't authored, but I believe you're
welcome to send a correction.

Thank you,
Geraldo Nascimento