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

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Date:   Tue, 8 Aug 2023 15:38:19 +0800
From:   Jiaxun Yang <jiaxun.yang@...goat.com>
To:     Huacai Chen <chenhuacai@...nel.org>
Cc:     linux-pci@...r.kernel.org, bhelgaas@...gle.com,
        linux-kernel@...r.kernel.org, kw@...ux.com, lpieralisi@...nel.org,
        stable@...r.kernel.org
Subject: Re: [PATCH v2] pci: loongson: Workaround MIPS firmware MRRS settings



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@...goat.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@...r.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@...goat.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()?

Hmm, I'm not sure this will work, since loongson_mrrs_quirk only run on 
bridges
but the old quirk should run on every single device.

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);