PCI/ASPM: Disable L1 before configuring L1 Substates

Per PCIe r6.1, sec 5.5.4, L1 must be disabled while setting ASPM L1 PM
Substates enable bits.  Previously this was enforced by clearing
PCI_EXP_LNKCTL_ASPMC before calling pci_restore_aspm_l1ss_state().

Move the L1 (and L0s, although that doesn't seem required) disable into
pci_restore_aspm_l1ss_state() itself so it's closer to the code that
depends on it.

Link: https://lore.kernel.org/r/20240223213733.GA115410@bhelgaasSigned-off-by: Bjorn Helgaas <bhelgaas@google.com>

drivers/pci/pci.c

@@ -1633,13 +1633,14 @@ static void pci_restore_pcie_state(struct pci_dev *dev)
 {
 	int i = 0;
 	struct pci_cap_saved_state *save_state;
-	u16 *cap, lnkctl;
+	u16 *cap;
 
 	/*
 	 * Restore max latencies (in the LTR capability) before enabling
 	 * LTR itself in PCI_EXP_DEVCTL2.
 	 */
 	pci_restore_ltr_state(dev);
+	pci_restore_aspm_l1ss_state(dev);
 
 	save_state = pci_find_saved_cap(dev, PCI_CAP_ID_EXP);
 	if (!save_state)
@@ -1654,23 +1655,12 @@ static void pci_restore_pcie_state(struct pci_dev *dev)
 
 	cap = (u16 *)&save_state->cap.data[0];
 	pcie_capability_write_word(dev, PCI_EXP_DEVCTL, cap[i++]);
-
-	/* Restore LNKCTL register with ASPM control field clear */
-	lnkctl = cap[i++];
-	pcie_capability_write_word(dev, PCI_EXP_LNKCTL,
-				   lnkctl & ~PCI_EXP_LNKCTL_ASPMC);
-
+	pcie_capability_write_word(dev, PCI_EXP_LNKCTL, cap[i++]);
 	pcie_capability_write_word(dev, PCI_EXP_SLTCTL, cap[i++]);
 	pcie_capability_write_word(dev, PCI_EXP_RTCTL, cap[i++]);
 	pcie_capability_write_word(dev, PCI_EXP_DEVCTL2, cap[i++]);
 	pcie_capability_write_word(dev, PCI_EXP_LNKCTL2, cap[i++]);
 	pcie_capability_write_word(dev, PCI_EXP_SLTCTL2, cap[i++]);
-
-	pci_restore_aspm_l1ss_state(dev);
-
-	/* Restore ASPM control after restoring L1SS state */
-	pcie_capability_set_word(dev, PCI_EXP_LNKCTL,
-				 lnkctl & PCI_EXP_LNKCTL_ASPMC);
 }
 
 static int pci_save_pcix_state(struct pci_dev *dev)

drivers/pci/pcie/aspm.c

@@ -105,6 +105,7 @@ void pci_restore_aspm_l1ss_state(struct pci_dev *pdev)
 	struct pci_dev *parent = pdev->bus->self;
 	u32 *cap, pl_ctl1, pl_ctl2, pl_l1_2_enable;
 	u32 cl_ctl1, cl_ctl2, cl_l1_2_enable;
+	u16 clnkctl, plnkctl;
 
 	/*
 	 * In case BIOS enabled L1.2 when resuming, we need to disable it first
@@ -129,6 +130,17 @@ void pci_restore_aspm_l1ss_state(struct pci_dev *pdev)
 	pl_ctl2 = *cap++;
 	pl_ctl1 = *cap;
 
+	/* Make sure L0s/L1 are disabled before updating L1SS config */
+	pcie_capability_read_word(pdev, PCI_EXP_LNKCTL, &clnkctl);
+	pcie_capability_read_word(parent, PCI_EXP_LNKCTL, &plnkctl);
+	if (FIELD_GET(PCI_EXP_LNKCTL_ASPMC, clnkctl) ||
+	    FIELD_GET(PCI_EXP_LNKCTL_ASPMC, plnkctl)) {
+		pcie_capability_write_word(pdev, PCI_EXP_LNKCTL,
+					   clnkctl & ~PCI_EXP_LNKCTL_ASPMC);
+		pcie_capability_write_word(parent, PCI_EXP_LNKCTL,
+					   plnkctl & ~PCI_EXP_LNKCTL_ASPMC);
+	}
+
 	/*
 	 * Disable L1.2 on this downstream endpoint device first, followed
 	 * by the upstream
@@ -161,6 +173,13 @@ void pci_restore_aspm_l1ss_state(struct pci_dev *pdev)
 		pci_write_config_dword(pdev, pdev->l1ss + PCI_L1SS_CTL1,
 				       cl_ctl1 | cl_l1_2_enable);
 	}
+
+	/* Restore L0s/L1 if they were enabled */
+	if (FIELD_GET(PCI_EXP_LNKCTL_ASPMC, clnkctl) ||
+	    FIELD_GET(PCI_EXP_LNKCTL_ASPMC, plnkctl)) {
+		pcie_capability_write_word(parent, PCI_EXP_LNKCTL, clnkctl);
+		pcie_capability_write_word(pdev, PCI_EXP_LNKCTL, plnkctl);
+	}
 }
 
 #ifdef CONFIG_PCIEASPM