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

[Huacai Chen <chenhuacai@kernel.org>]

Hi, Jiaxun,

On Sun, Aug 6, 2023 at 10:20 AM Jiaxun Yang <jiaxun.yang@flygoat.com> 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@vger.kernel.org
> > 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@flygoat.com>
>
> Ping?
> I expect this patch to go through PCI fixes tree.
Can we do it like this by modifying the existing loongson_mrrs_quirk()?

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);
>