Re: [PATCH v2] pci: loongson: Workaround MIPS firmware MRRS settings

[Huacai Chen]

Hi, Jiaxun,

On Tue, Aug 8, 2023 at 3:38 PM Jiaxun Yang <jiaxun.yang@xxxxxxxxxxx> wrote:
>
>
>
> 在 2023/8/6 22:30, Huacai Chen 写道:
> > Hi, Jiaxun,
> >
> > On Sun, Aug 6, 2023 at 10:20 AM Jiaxun Yang <jiaxun.yang@xxxxxxxxxxx> wrote:
> >>
> >>
> >> 在 2023/7/25 14:10, Jiaxun Yang 写道:
> >>> 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.
> >>>
> >>> Cc: stable@xxxxxxxxxxxxxxx
> >>> 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>
> >> Ping?
> >> I expect this patch to go through PCI fixes tree.
> > Can we do it like this by modifying the existing loongson_mrrs_quirk()?
>
> Hmm, I'm not sure this will work, since loongson_mrrs_quirk only run on
> bridges
But it is worth to try, and you can walk the children to set mrrs when
the quirk runs on bridges, I think.

> but the old quirk should run on every single device.
Your current patch has a drawback that both quirks will run for MIPS,
and their order is random (though it may cause nothing, but not
elegant).

Huacai

>
> Thanks
> Jiaxun
>
> >
> > 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 = pci_find_host_bridge(pdev->bus);
> >
> > #ifdef CONFIG_MIPS
> >          set_pcie_ports_to_mrrs_256_to_emulate_the_firmware_behavior();
> > #endif
> >
> >          bridge->no_inc_mrrs = 1;
> > }
> >
> >> Thanks
> >> - Jiaxun
> >>
> >>> ---
> >>> v2: Rename quirk name to: loongson_old_mrrs_quirk
> >>> ---
> >>>    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..d0f68b102d10 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_old_mrrs_quirk(struct pci_dev *pdev)
> >>> +{
> >>> +     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_old_mrrs_quirk);
> >>> +#endif
> >>> +
> >>>    static void loongson_pci_pin_quirk(struct pci_dev *pdev)
> >>>    {
> >>>        pdev->pin = 1 + (PCI_FUNC(pdev->devfn) & 3);
>