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

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Message-Id: <20230725061008.1504292-1-jiaxun.yang@flygoat.com>
Date:   Tue, 25 Jul 2023 14:10:08 +0800
From:   Jiaxun Yang <jiaxun.yang@...goat.com>
To:     linux-pci@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, chenhuacai@...nel.org,
        bhelgaas@...gle.com, kw@...ux.com, lpieralisi@...nel.org,
        Jiaxun Yang <jiaxun.yang@...goat.com>, stable@...r.kernel.org
Subject: [PATCH v2] pci: loongson: Workaround MIPS firmware MRRS settings

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>
---
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);
-- 
2.39.2