On Fri, Dec 01, 2023 at 11:50:28AM +0000, Jiaxun Yang 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@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>
Applied to for-linus for v6.7, thanks!
> ---
> 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/controller/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 = 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;
> +
> + 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_quirk);
> +#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 = pci_find_host_bridge(pdev->bus);
>
> bridge->no_inc_mrrs = 1;
> --
> 2.34.1
>
