Re: [PATCH] pci: loongson: Workaround MIPS firmware MRRS settings

[Huacai Chen]

Hi, Jiaxun,

On Tue, Jul 18, 2023 at 9:33 PM Jiaxun Yang <jiaxun.yang@xxxxxxxxxxx> wrote:
>
> This is a partial revert of commit 8b3517f88ff2 ("PCI:
> loongson: Prevent LS7A MRRS increases") for MIPS based Loongson.
>
> There are many MIPS based Loongson systems in wild that
> shipped with firmware which does not set maximum MRRS properly.
>
> Limiting MRRS to 256 for all as MIPS Loongson comes with higher
> MRRS support is considered rare.
>
> Closes: https://bugzilla.kernel.org/show_bug.cgi?id=217680
> Fixes: 8b3517f88ff2 ("PCI: loongson: Prevent LS7A MRRS increases")
> Signed-off-by: Jiaxun Yang <jiaxun.yang@xxxxxxxxxxx>
> ---
>  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 fe0f732f6e43..1cc3a5535dac 100644
> --- a/drivers/pci/controller/pci-loongson.c
> +++ b/drivers/pci/controller/pci-loongson.c
> @@ -108,6 +108,44 @@ DECLARE_PCI_FIXUP_EARLY(PCI_VENDOR_ID_LOONGSON,
>  DECLARE_PCI_FIXUP_EARLY(PCI_VENDOR_ID_LOONGSON,
>                         DEV_LS7A_PCIE_PORT6, loongson_mrrs_quirk);
>
> +#ifdef CONFIG_MIPS
> +static void loongson_firmware_mrrs_quirk(struct pci_dev *pdev)
>From my point of view, loongson_old_mrrs_quirk() may be better.

Huacai

> +{
> +       struct pci_bus *bus = pdev->bus;
> +       struct pci_dev *bridge;
> +       static const struct pci_device_id bridge_devids[] = {
> +               { PCI_VDEVICE(LOONGSON, DEV_LS2K_PCIE_PORT0) },
> +               { PCI_VDEVICE(LOONGSON, DEV_LS7A_PCIE_PORT0) },
> +               { PCI_VDEVICE(LOONGSON, DEV_LS7A_PCIE_PORT1) },
> +               { PCI_VDEVICE(LOONGSON, DEV_LS7A_PCIE_PORT2) },
> +               { PCI_VDEVICE(LOONGSON, DEV_LS7A_PCIE_PORT3) },
> +               { PCI_VDEVICE(LOONGSON, DEV_LS7A_PCIE_PORT4) },
> +               { PCI_VDEVICE(LOONGSON, DEV_LS7A_PCIE_PORT5) },
> +               { PCI_VDEVICE(LOONGSON, DEV_LS7A_PCIE_PORT6) },
> +               { 0, },
> +       };
> +
> +       /* look for the matching bridge */
> +       while (!pci_is_root_bus(bus)) {
> +               bridge = bus->self;
> +               bus = bus->parent;
> +               /*
> +                * There are still some wild MIPS Loongson firmware won't
> +                * set MRRS properly. Limiting MRRS to 256 as MIPS Loongson
> +                * comes with higher MRRS support is considered rare.
> +                */
> +               if (pci_match_id(bridge_devids, bridge)) {
> +                       if (pcie_get_readrq(pdev) > 256) {
> +                               pci_info(pdev, "limiting MRRS to 256\n");
> +                               pcie_set_readrq(pdev, 256);
> +                       }
> +                       break;
> +               }
> +       }
> +}
> +DECLARE_PCI_FIXUP_ENABLE(PCI_ANY_ID, PCI_ANY_ID, loongson_firmware_mrrs_quirk);
> +#endif
> +
>  static void loongson_pci_pin_quirk(struct pci_dev *pdev)
>  {
>         pdev->pin = 1 + (PCI_FUNC(pdev->devfn) & 3);
> --
> 2.39.2
>