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Message-ID: <CAAhV-H6=Q33SXNDGbWVMAQjBeH-26qj0d-E-pKZhgpS5DWu75g@mail.gmail.com>
Date: Sat, 10 Jan 2026 11:56:28 +0800
From: Huacai Chen <chenhuacai@...nel.org>
To: liziyao@...ontech.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>,
niecheng1@...ontech.com, zhanjun@...ontech.com, guanwentao@...ontech.com,
Kexy Biscuit <kexybiscuit@...c.io>, linux-pci@...r.kernel.org,
linux-kernel@...r.kernel.org, loongarch@...ts.linux.dev,
Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>,
Lain Fearyncess Yang <fsf@...e.com>, Ayden Meng <aydenmeng@...h.net>, Mingcong Bai <jeffbai@...c.io>,
Xi Ruoyao <xry111@...111.site>
Subject: Re: [PATCH v3] PCI: loongson: Override PCIe bridge supported speeds
for older Loongson 3C6000 series steppings
Hi, Ziyao,
As far as I know, new chips may still use the same PCI ID, and even if
new chips fix this problem in hardware, this patch seems harmless. So
I suggest the subject to be:
PCI: loongson: Override PCIe bridge supported speeds for Loongson-3C6000 series.
On Fri, Jan 9, 2026 at 11:37 AM Ziyao Li via B4 Relay
<devnull+liziyao.uniontech.com@...nel.org> wrote:
>
> From: Ziyao Li <liziyao@...ontech.com>
>
> Older steppings of the Loongson 3C6000 series incorrectly report the
> supported link speeds on their PCIe bridges (device IDs 3c19, 3c29) as
> only 2.5 GT/s, despite the upstream bus supporting speeds from 2.5 GT/s
> up to 16 GT/s.
Please use Loongson-3C6000 instead of Loongson 3C6000, and use
0x3c19/0x3c29 instead of 3c19/3c29, thanks.
Huacai
>
> As a result, since commit 774c71c52aa4 ("PCI/bwctrl: Enable only if more
> than one speed is supported"), bwctrl will be disabled if there's only
> one 2.5 GT/s value in vector `supported_speeds`.
>
> Also, amdgpu reads the value by pcie_get_speed_cap() in amdgpu_device_
> partner_bandwidth(), for its dynamic adjustment of PCIe clocks and
> lanes in power management. We hope this can prevent similar problems
> in future driver changes (similar checks may be implemented in other
> GPU, storage controller, NIC, etc. drivers).
>
> Manually override the `supported_speeds` field for affected PCIe bridges
> with those found on the upstream bus to correctly reflect the supported
> link speeds.
>
> This patch was originally found from AOSC OS[1].
>
> Link: https://github.com/AOSC-Tracking/linux/pull/2 #1
> Tested-by: Lain Fearyncess Yang <fsf@...e.com>
> Tested-by: Ayden Meng <aydenmeng@...h.net>
> Signed-off-by: Ayden Meng <aydenmeng@...h.net>
> Signed-off-by: Mingcong Bai <jeffbai@...c.io>
> [Xi Ruoyao: Fix falling through logic and add kernel log output.]
> Signed-off-by: Xi Ruoyao <xry111@...111.site>
> Link: https://github.com/AOSC-Tracking/linux/commit/4392f441363abdf6fa0a0433d73175a17f493454
> [Ziyao Li: move from drivers/pci/quirks.c to drivers/pci/controller/pci-loongson.c]
> Signed-off-by: Ziyao Li <liziyao@...ontech.com>
> Tested-by: Mingcong Bai <jeffbai@...c.io>
> ---
> Changes in v3:
> - Adjust commit message
> - Make the program flow more intuitive
> - Link to v2: https://lore.kernel.org/r/20260104-loongson-pci1-v2-1-d151e57b6ef8@uniontech.com
>
> Changes in v2:
> - Link to v1: https://lore.kernel.org/r/20250822-loongson-pci1-v1-1-39aabbd11fbd@uniontech.com
> - Move from arch/loongarch/pci/pci.c to drivers/pci/controller/pci-loongson.c
> - Fix falling through logic and add kernel log output by Xi Ruoyao
> ---
> drivers/pci/controller/pci-loongson.c | 38 +++++++++++++++++++++++++++++++++++
> 1 file changed, 38 insertions(+)
>
> diff --git a/drivers/pci/controller/pci-loongson.c b/drivers/pci/controller/pci-loongson.c
> index bc630ab8a283..67a6d99b9e82 100644
> --- a/drivers/pci/controller/pci-loongson.c
> +++ b/drivers/pci/controller/pci-loongson.c
> @@ -176,6 +176,44 @@ static void loongson_pci_msi_quirk(struct pci_dev *dev)
> }
> DECLARE_PCI_FIXUP_FINAL(PCI_VENDOR_ID_LOONGSON, DEV_LS7A_PCIE_PORT5, loongson_pci_msi_quirk);
>
> +/*
> + * Older steppings of the Loongson 3C6000 series incorrectly report the
> + * supported link speeds on their PCIe bridges (device IDs 3c19, 3c29) as
> + * only 2.5 GT/s, despite the upstream bus supporting speeds from 2.5 GT/s
> + * up to 16 GT/s.
> + */
> +static void loongson_pci_bridge_speed_quirk(struct pci_dev *pdev)
> +{
> + u8 old_supported_speeds = pdev->supported_speeds;
> +
> + switch (pdev->bus->max_bus_speed) {
> + case PCIE_SPEED_16_0GT:
> + pdev->supported_speeds |= PCI_EXP_LNKCAP2_SLS_16_0GB;
> + fallthrough;
> + case PCIE_SPEED_8_0GT:
> + pdev->supported_speeds |= PCI_EXP_LNKCAP2_SLS_8_0GB;
> + fallthrough;
> + case PCIE_SPEED_5_0GT:
> + pdev->supported_speeds |= PCI_EXP_LNKCAP2_SLS_5_0GB;
> + fallthrough;
> + case PCIE_SPEED_2_5GT:
> + pdev->supported_speeds |= PCI_EXP_LNKCAP2_SLS_2_5GB;
> + break;
> + default:
> + pci_warn(pdev, "unexpected max bus speed");
> +
> + return;
> + }
> +
> + if (pdev->supported_speeds != old_supported_speeds)
> + pci_info(pdev, "fixing up supported link speeds: 0x%x => 0x%x",
> + old_supported_speeds, pdev->supported_speeds);
> +}
> +DECLARE_PCI_FIXUP_HEADER(PCI_VENDOR_ID_LOONGSON, 0x3c19,
> + loongson_pci_bridge_speed_quirk);
> +DECLARE_PCI_FIXUP_HEADER(PCI_VENDOR_ID_LOONGSON, 0x3c29,
> + loongson_pci_bridge_speed_quirk);
> +
> static struct loongson_pci *pci_bus_to_loongson_pci(struct pci_bus *bus)
> {
> struct pci_config_window *cfg;
>
> ---
> base-commit: ea1013c1539270e372fc99854bc6e4d94eaeff66
> change-id: 20250822-loongson-pci1-4ded0d78f1bb
>
> Best regards,
> --
> Ziyao Li <liziyao@...ontech.com>
>
>
>
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