PCI/ASPM: Add pcie_aspm_remove_cap() to override advertised link states

Add pcie_aspm_remove_cap().  A quirk can use this to prevent use of ASPM
L0s or L1 link states, even if the device advertised support for them.

Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Tested-by: Shawn Lin <shawn.lin@rock-chips.com>
Reviewed-by: Lukas Wunner <lukas@wunner.de>
Link: https://patch.msgid.link/20251110222929.2140564-3-helgaas@kernel.org

Author: bjorn-helgaas

drivers/pci/pci.h

@@ -958,13 +958,15 @@ void pci_save_aspm_l1ss_state(struct pci_dev *dev);
 void pci_restore_aspm_l1ss_state(struct pci_dev *dev);
 
 #ifdef CONFIG_PCIEASPM
+void pcie_aspm_remove_cap(struct pci_dev *pdev, u32 lnkcap);
 void pcie_aspm_init_link_state(struct pci_dev *pdev);
 void pcie_aspm_exit_link_state(struct pci_dev *pdev);
 void pcie_aspm_pm_state_change(struct pci_dev *pdev, bool locked);
 void pcie_aspm_powersave_config_link(struct pci_dev *pdev);
 void pci_configure_ltr(struct pci_dev *pdev);
 void pci_bridge_reconfigure_ltr(struct pci_dev *pdev);
 #else
+static inline void pcie_aspm_remove_cap(struct pci_dev *pdev, u32 lnkcap) { }
 static inline void pcie_aspm_init_link_state(struct pci_dev *pdev) { }
 static inline void pcie_aspm_exit_link_state(struct pci_dev *pdev) { }
 static inline void pcie_aspm_pm_state_change(struct pci_dev *pdev, bool locked) { }

drivers/pci/pcie/aspm.c

@@ -1542,6 +1542,19 @@ int pci_enable_link_state_locked(struct pci_dev *pdev, int state)
 }
 EXPORT_SYMBOL(pci_enable_link_state_locked);
 
+void pcie_aspm_remove_cap(struct pci_dev *pdev, u32 lnkcap)
+{
+	if (lnkcap & PCI_EXP_LNKCAP_ASPM_L0S)
+		pdev->aspm_l0s_support = 0;
+	if (lnkcap & PCI_EXP_LNKCAP_ASPM_L1)
+		pdev->aspm_l1_support = 0;
+
+	pci_info(pdev, "ASPM: Link Capabilities%s%s treated as unsupported to avoid device defect\n",
+		 lnkcap & PCI_EXP_LNKCAP_ASPM_L0S ? " L0s" : "",
+		 lnkcap & PCI_EXP_LNKCAP_ASPM_L1 ? " L1" : "");
+
+}
+
 static int pcie_aspm_set_policy(const char *val,
 				const struct kernel_param *kp)
 {