PCI/ASPM: Move pci_configure_ltr() to aspm.c

The Latency Tolerance Reporting (LTR) mechanism supports the ASPM L1.2
state and is only configured when CONFIG_PCIEASPM is set.

Move pci_configure_ltr() and pci_bridge_reconfigure_ltr() into aspm.c since
they only build when CONFIG_PCIEASPM is set.  No functional change
intended.

Suggested-by: Bjorn Helgaas <bhelgaas@google.com>
Link: https://lore.kernel.org/r/20240128233212.1139663-2-david.e.box@linux.intel.com
[bhelgaas: commit log, split build change from function moves]
Link: https://lore.kernel.org/r/20240223205851.114931-2-helgaas@kernel.org
Signed-off-by: David E. Box <david.e.box@linux.intel.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>

1 files changed, 75 insertions, 0 deletions

diff --git a/drivers/pci/pcie/aspm.c b/drivers/pci/pcie/aspm.c
index 5a0066ecc3c5..d1538f73f2f9 100644
--- a/drivers/pci/pcie/aspm.c
+++ b/drivers/pci/pcie/aspm.c
@@ -938,6 +938,81 @@ out:
 	up_read(&pci_bus_sem);
 }
 
+void pci_bridge_reconfigure_ltr(struct pci_dev *pdev)
+{
+	struct pci_dev *bridge;
+	u32 ctl;
+
+	bridge = pci_upstream_bridge(pdev);
+	if (bridge && bridge->ltr_path) {
+		pcie_capability_read_dword(bridge, PCI_EXP_DEVCTL2, &ctl);
+		if (!(ctl & PCI_EXP_DEVCTL2_LTR_EN)) {
+			pci_dbg(bridge, "re-enabling LTR\n");
+			pcie_capability_set_word(bridge, PCI_EXP_DEVCTL2,
+						 PCI_EXP_DEVCTL2_LTR_EN);
+		}
+	}
+}
+
+void pci_configure_ltr(struct pci_dev *pdev)
+{
+	struct pci_host_bridge *host = pci_find_host_bridge(pdev->bus);
+	struct pci_dev *bridge;
+	u32 cap, ctl;
+
+	if (!pci_is_pcie(pdev))
+		return;
+
+	/* Read L1 PM substate capabilities */
+	pdev->l1ss = pci_find_ext_capability(pdev, PCI_EXT_CAP_ID_L1SS);
+
+	pcie_capability_read_dword(pdev, PCI_EXP_DEVCAP2, &cap);
+	if (!(cap & PCI_EXP_DEVCAP2_LTR))
+		return;
+
+	pcie_capability_read_dword(pdev, PCI_EXP_DEVCTL2, &ctl);
+	if (ctl & PCI_EXP_DEVCTL2_LTR_EN) {
+		if (pci_pcie_type(pdev) == PCI_EXP_TYPE_ROOT_PORT) {
+			pdev->ltr_path = 1;
+			return;
+		}
+
+		bridge = pci_upstream_bridge(pdev);
+		if (bridge && bridge->ltr_path)
+			pdev->ltr_path = 1;
+
+		return;
+	}
+
+	if (!host->native_ltr)
+		return;
+
+	/*
+	 * Software must not enable LTR in an Endpoint unless the Root
+	 * Complex and all intermediate Switches indicate support for LTR.
+	 * PCIe r4.0, sec 6.18.
+	 */
+	if (pci_pcie_type(pdev) == PCI_EXP_TYPE_ROOT_PORT) {
+		pcie_capability_set_word(pdev, PCI_EXP_DEVCTL2,
+					 PCI_EXP_DEVCTL2_LTR_EN);
+		pdev->ltr_path = 1;
+		return;
+	}
+
+	/*
+	 * If we're configuring a hot-added device, LTR was likely
+	 * disabled in the upstream bridge, so re-enable it before enabling
+	 * it in the new device.
+	 */
+	bridge = pci_upstream_bridge(pdev);
+	if (bridge && bridge->ltr_path) {
+		pci_bridge_reconfigure_ltr(pdev);
+		pcie_capability_set_word(pdev, PCI_EXP_DEVCTL2,
+					 PCI_EXP_DEVCTL2_LTR_EN);
+		pdev->ltr_path = 1;
+	}
+}
+
 /* Recheck latencies and update aspm_capable for links under the root */
 static void pcie_update_aspm_capable(struct pcie_link_state *root)
 {