linux-kernel - Re: [PATCH v6] pci: loongson: Workaround MIPS firmware MRRS settings

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Message-ID: <20231208165039.GA796094@bhelgaas>
Date:   Fri, 8 Dec 2023 10:50:39 -0600
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     Jiaxun Yang <jiaxun.yang@...goat.com>
Cc:     linux-pci@...r.kernel.org, lpieralisi@...nel.org, kw@...ux.com,
        robh@...nel.org, linux-kernel@...r.kernel.org,
        chenhuacai@...nel.org, stable@...r.kernel.org
Subject: Re: [PATCH v6] pci: loongson: Workaround MIPS firmware MRRS settings

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@...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>

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
>