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

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Date:   Thu, 7 Sep 2023 06:48:28 +0530
From:   Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
To:     Jiaxun Yang <jiaxun.yang@...goat.com>
Cc:     Huacai Chen <chenhuacai@...nel.org>, 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

On Tue, Aug 08, 2023 at 03:38:19PM +0800, Jiaxun Yang 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@...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.
> 

Why do you need to walk through every single device instead of just bridges?
I'm not the maintainer, but my suggestion is to go for Huacai Chen's solution.

This avoids iterating over bridges/devices two times.

Also, please rename firmware to BIOS, as firmware commonly represents the
software running on PCIe endpoint devices.

- Mani

> 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);
> 

-- 
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