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From:   Huacai Chen <chenhuacai@kernel.org>
Date:   Sat, 2 Dec 2023 11:01:00 +0800
Message-ID: <CAAhV-H6+goYrqQ_LAPMFZ9gJrr-tDHSkesnTwAdqCYNdB_GPZQ@mail.gmail.com>
Subject: Re: [PATCH v6] pci: loongson: Workaround MIPS firmware MRRS settings
To:     Jiaxun Yang <jiaxun.yang@flygoat.com>
Cc:     linux-pci@vger.kernel.org, lpieralisi@kernel.org, kw@linux.com,
        robh@kernel.org, linux-kernel@vger.kernel.org,
        stable@vger.kernel.org
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Acked-by: Huacai Chen <chenhuacai@loongson.cn>

On Fri, Dec 1, 2023 at 7:50=E2=80=AFPM Jiaxun Yang <jiaxun.yang@flygoat.com=
> 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.
>
> It must be done at device enablement stage because MRRS setting
> may get lost if the parent bridge lost PCI_COMMAND_MASTER, and
> we are only sure parent bridge is enabled at this point.
>
> Cc: stable@vger.kernel.org
> Closes: https://bugzilla.kernel.org/show_bug.cgi?id=3D217680
> Fixes: 8b3517f88ff2 ("PCI: loongson: Prevent LS7A MRRS increases")
> Signed-off-by: Jiaxun Yang <jiaxun.yang@flygoat.com>
> ---
> v4: Improve commit message
> v5:
>         - Improve commit message and comments.
>         - Style fix from Huacai's off-list input.
> v6: Fix a typo
> ---
>  drivers/pci/controller/pci-loongson.c | 47 ++++++++++++++++++++++++---
>  1 file changed, 42 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/pci/controller/pci-loongson.c b/drivers/pci/controll=
er/pci-loongson.c
> index d45e7b8dc530..e181d99decf1 100644
> --- a/drivers/pci/controller/pci-loongson.c
> +++ b/drivers/pci/controller/pci-loongson.c
> @@ -80,13 +80,50 @@ DECLARE_PCI_FIXUP_EARLY(PCI_VENDOR_ID_LOONGSON,
>  DECLARE_PCI_FIXUP_EARLY(PCI_VENDOR_ID_LOONGSON,
>                         DEV_LS7A_LPC, system_bus_quirk);
>
> +/*
> + * Some Loongson PCIe ports have h/w limitations of maximum read
> + * request size. They can't handle anything larger than this.
> + * Sane firmware will set proper MRRS at boot, so we only need
> + * no_inc_mrrs for bridges. However, some MIPS Loongson firmware
> + * won't set MRRS properly, and we have to enforce maximum safe
> + * MRRS, which is 256 bytes.
> + */
> +#ifdef CONFIG_MIPS
> +static void loongson_set_min_mrrs_quirk(struct pci_dev *pdev)
> +{
> +       struct pci_bus *bus =3D pdev->bus;
> +       struct pci_dev *bridge;
> +       static const struct pci_device_id bridge_devids[] =3D {
> +               { 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 =3D bus->self;
> +               bus =3D bus->parent;
> +
> +               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_set_min_mrrs_q=
uirk);
> +#endif
> +
>  static void loongson_mrrs_quirk(struct pci_dev *pdev)
>  {
> -       /*
> -        * Some Loongson PCIe ports have h/w limitations of maximum read
> -        * request size. They can't handle anything larger than this. So
> -        * force this limit on any devices attached under these ports.
> -        */
>         struct pci_host_bridge *bridge =3D pci_find_host_bridge(pdev->bus=
);
>
>         bridge->no_inc_mrrs =3D 1;
> --
> 2.34.1
>