linux-kernel - Re: [PATCH] PCI: dw-rockchip: Skip waiting for link up

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Message-Id: <DE3DPAVIOGZP.7RW4SGB8HXUT@cknow-tech.com>
Date: Sat, 08 Nov 2025 15:21:45 +0100
From: "Diederik de Haas" <diederik@...ow-tech.com>
To: "Niklas Cassel" <cassel@...nel.org>, "Shawn Lin"
 <shawn.lin@...k-chips.com>
Cc: "FUKAUMI Naoki" <naoki@...xa.com>, "Damien Le Moal"
 <dlemoal@...nel.org>, "Anand Moon" <linux.amoon@...il.com>,
 <linux-pci@...r.kernel.org>, <linux-arm-kernel@...ts.infradead.org>,
 <linux-rockchip@...ts.infradead.org>, <linux-kernel@...r.kernel.org>,
 "Dragan Simic" <dsimic@...jaro.org>, "Lorenzo Pieralisi"
 <lpieralisi@...nel.org>, Krzysztof Wilczyński
 <kw@...ux.com>, "Manivannan Sadhasivam" <manivannan.sadhasivam@...aro.org>,
 "Rob Herring" <robh@...nel.org>, "Bjorn Helgaas" <bhelgaas@...gle.com>,
 "Heiko Stuebner" <heiko@...ech.de>
Subject: Re: [PATCH] PCI: dw-rockchip: Skip waiting for link up

On Sat Nov 8, 2025 at 2:27 PM CET, Niklas Cassel wrote:
> On Sat, Nov 08, 2025 at 01:34:32PM +0100, Niklas Cassel wrote:
>> 
>> The pcie-dw-rockchip.c driver is modelled after the qcom driver.
>> So if this is a problem when a ASM2806 switch is connected, I would
>> expect qcom platforms to have the same problem.
>
> Looking more closely at this, comparing the "good" kernel:

There's another thing that caught my eye ...

> [    1.868857] pci 0004:40:00.0: [1d87:3588] type 01 class 0x060400 PCIe Root Port
> [    1.869509] pci 0004:40:00.0: ROM [mem 0x00000000-0x0000ffff pref]
> ...
> [    1.879764] pci 0004:41:00.0: enabling Extended Tags
> [    1.880614] pci 0004:41:00.0: PME# supported from D0 D3hot D3cold
> [    1.881409] pci 0004:41:00.0: 2.000 Gb/s available PCIe bandwidth, limited by 2.5 GT/s PCIe x1 link at 0004:40:00.0 (capable of 15.752 Gb/s with 8.0 GT/s PCIe x2 link)

... 2.000 Gb/s ...

> [    1.888729] pci 0004:41:00.0: bridge configuration invalid ([bus 00-00]), reconfiguring
> ...
>
>
> With the "bad" kernel:
> [    1.383075] pci 0004:40:00.0: [1d87:3588] type 01 class 0x060400 PCIe Root Port
> [    1.383738] pci 0004:40:00.0: ROM [mem 0x00000000-0x0000ffff pref]
> ...
> [    1.415746] pci 0004:41:00.0: enabling Extended Tags
> [    1.416465] pci 0004:41:00.0: PME# supported from D0 D3hot D3cold
> [    1.417181] pci 0004:41:00.0: 4.000 Gb/s available PCIe bandwidth, limited by 5.0 GT/s PCIe x1 link at 0004:40:00.0 (capable of 15.752 Gb/s with 8.0 GT/s PCIe x2 link)

... 4.0000 Gb/s

I don't know if that's relevant or important, but wanted to mention it.

Cheers,
  Diederik

> [    1.423384] pci 0004:41:00.0: bridge configuration invalid ([bus 00-00]), reconfiguring
> ...
>
>
> We can see that the pcie-dw-rockchip.c driver detects the ASM2806 switch
> in both cases. So the problem is not really with enumerating the root port.
>
> The problem seems to be that with the "bad" kernel, you get a lot of:
> [    1.464651] pci 0004:42:00.0: devices behind bridge are unusable because [bus 43] cannot be assigned for them
>
> Because the bus ends are different, and conflicts with each other.
> I don't know why this happens.
>
> Perhaps we could add a quirk for ASM2806 that does some extra sleep if that
> switch is detected, if for some reason, the switch is not actually ready
> after the delays defined by the PCIe specification.
>
> (And btw. please test with the latest 6.18-rc, as, from experience, the
> ASPM problems in earlier RCs can result in some weird problems that are
> not immediately deduced to be caused by the ASPM enablement.)
>
>
> Kind regards,
> Niklas