FROMLIST: PCI: Override PCIe bridge supported speeds for older Loongson 3C6000 series steppings

Ziyao · MingcongBai · commit 72abf0802557 · 2025-09-09T16:34:09.000+08:00
Older steppings of the Loongson 3C6000 series incorrectly report the supported link speeds on their PCIe bridges (device IDs 3c19, 3c29) as only 2.5 GT/s, despite the upstream bus supporting speeds from 2.5 GT/s up to 16 GT/s. As a result, certain PCIe devices would be incorrectly probed as a Gen1- only, even if higher link speeds are supported, harming performance and prevents dynamic link speed functionality from being enabled in drivers such as amdgpu. Manually override the `supported_speeds` field for affected PCIe bridges with those found on the upstream bus to correctly reflect the supported link speeds. This patch is found from AOSC OS[1]. Link: #2 #1 Tested-by: Lain Fearyncess Yang <fsf@live.com> Tested-by: Mingcong Bai <jeffbai@aosc.io> Tested-by: Ayden Meng <aydenmeng@yeah.net> Signed-off-by: Ayden Meng <aydenmeng@yeah.net> Signed-off-by: Ziyao <liziyao@uniontech.com> Link: https://lore.kernel.org/loongarch/20250822-loongson-pci1-v1-1-39aabbd11fbd@uniontech.com/ Signed-off-by: Mingcong Bai <jeffbai@aosc.io>
diff --git a/drivers/pci/quirks.c b/drivers/pci/quirks.c
@@ -1956,6 +1956,30 @@ DECLARE_PCI_FIXUP_FINAL(PCI_VENDOR_ID_INTEL,	PCI_DEVICE_ID_INTEL_E7525_MCH,	quir
 
 DECLARE_PCI_FIXUP_CLASS_FINAL(PCI_VENDOR_ID_HUAWEI, 0x1610, PCI_CLASS_BRIDGE_PCI, 8, quirk_pcie_mch);
 
+/*
+ * Older steppings of the Loongson 3C6000 series incorrectly report the
+ * supported link speeds on their PCIe bridges (device IDs 3c19, 3c29) as
+ * only 2.5 GT/s, despite the upstream bus supporting speeds from 2.5 GT/s
+ * up to 16 GT/s.
+ */
+static void quirk_loongson_pci_bridge_supported_speeds(struct pci_dev *pdev)
+{
+	switch (pdev->bus->max_bus_speed) {
+	case PCIE_SPEED_16_0GT:
+		pdev->supported_speeds |= PCI_EXP_LNKCAP2_SLS_16_0GB;
+	case PCIE_SPEED_8_0GT:
+		pdev->supported_speeds |= PCI_EXP_LNKCAP2_SLS_8_0GB;
+	case PCIE_SPEED_5_0GT:
+		pdev->supported_speeds |= PCI_EXP_LNKCAP2_SLS_5_0GB;
+	case PCIE_SPEED_2_5GT:
+		pdev->supported_speeds |= PCI_EXP_LNKCAP2_SLS_2_5GB;
+	default:
+		break;
+	}
+}
+DECLARE_PCI_FIXUP_HEADER(PCI_VENDOR_ID_LOONGSON, 0x3c19, quirk_loongson_secondary_bridge_supported_speeds);
+DECLARE_PCI_FIXUP_HEADER(PCI_VENDOR_ID_LOONGSON, 0x3c29, quirk_loongson_secondary_bridge_supported_speeds);
+
 /*
  * HiSilicon KunPeng920 and KunPeng930 have devices appear as PCI but are
  * actually on the AMBA bus. These fake PCI devices can support SVA via
