PCI/ASPM: Save parent L1SS config in pci_save_aspm_l1ss_state()

After 1742336 ("PCI/ASPM: Save L1 PM Substates Capability for
suspend/resume"), pci_save_aspm_l1ss_state(dev) saves the L1SS state for
"dev", and pci_restore_aspm_l1ss_state(dev) restores the state for both
"dev" and its parent.

The problem is that unless pci_save_state() has been used in some other
path and has already saved the parent L1SS state, we will restore junk to
the parent, which means the L1 Substates likely won't work correctly.

Save the L1SS config for both the device and its parent in
pci_save_aspm_l1ss_state().  When restoring, we need both because L1SS must
be enabled at the parent (the Downstream Port) before being enabled at the
child (the Upstream Port).

Link: https://lore.kernel.org/r/[email protected]
Fixes: 1742336 ("PCI/ASPM: Save L1 PM Substates Capability for suspend/resume")
Closes: https://bugzilla.kernel.org/show_bug.cgi?id=218394
Suggested-by: Ilpo Järvinen <[email protected]>
Signed-off-by: Jian-Hong Pan <[email protected]>
[bhelgaas: parallel save/restore structure, simplify commit log, patch at
https://lore.kernel.org/r/20241212230340.GA3267194@bhelgaas]
Signed-off-by: Bjorn Helgaas <[email protected]>
Tested-by: Jian-Hong Pan <[email protected]> # Asus B1400CEAE

Author: starnight

drivers/pci/pcie/aspm.c

@@ -81,24 +81,47 @@ void pci_configure_aspm_l1ss(struct pci_dev *pdev)
 
 void pci_save_aspm_l1ss_state(struct pci_dev *pdev)
 {
+	struct pci_dev *parent = pdev->bus->self;
 	struct pci_cap_saved_state *save_state;
-	u16 l1ss = pdev->l1ss;
 	u32 *cap;
 
+	/*
+	 * If this is a Downstream Port, we never restore the L1SS state
+	 * directly; we only restore it when we restore the state of the
+	 * Upstream Port below it.
+	 */
+	if (pcie_downstream_port(pdev) || !parent)
+		return;
+
+	if (!pdev->l1ss || !parent->l1ss)
+		return;
+
 	/*
 	 * Save L1 substate configuration. The ASPM L0s/L1 configuration
 	 * in PCI_EXP_LNKCTL_ASPMC is saved by pci_save_pcie_state().
 	 */
-	if (!l1ss)
+	save_state = pci_find_saved_ext_cap(pdev, PCI_EXT_CAP_ID_L1SS);
+	if (!save_state)
 		return;
 
-	save_state = pci_find_saved_ext_cap(pdev, PCI_EXT_CAP_ID_L1SS);
+	cap = &save_state->cap.data[0];
+	pci_read_config_dword(pdev, pdev->l1ss + PCI_L1SS_CTL2, cap++);
+	pci_read_config_dword(pdev, pdev->l1ss + PCI_L1SS_CTL1, cap++);
+
+	if (parent->state_saved)
+		return;
+
+	/*
+	 * Save parent's L1 substate configuration so we have it for
+	 * pci_restore_aspm_l1ss_state(pdev) to restore.
+	 */
+	save_state = pci_find_saved_ext_cap(parent, PCI_EXT_CAP_ID_L1SS);
 	if (!save_state)
 		return;
 
 	cap = &save_state->cap.data[0];
-	pci_read_config_dword(pdev, l1ss + PCI_L1SS_CTL2, cap++);
-	pci_read_config_dword(pdev, l1ss + PCI_L1SS_CTL1, cap++);
+	pci_read_config_dword(parent, parent->l1ss + PCI_L1SS_CTL2, cap++);
+	pci_read_config_dword(parent, parent->l1ss + PCI_L1SS_CTL1, cap++);
 }
 
 void pci_restore_aspm_l1ss_state(struct pci_dev *pdev)