[PATCH v2] backports: Add return value to backport_pci_disable_link_state()

Since Linux upstream commit 4cfd21885592 ("PCI: let
pci_disable_link_state propagate errors") The
backport_pci_disable_link_state() function can return an error. This
return code is now used by the mt76 driver.

In case it is not possible to disable ASPM, for example on some ACPI
systems, we should return an error and mt76 handles this. Do this by
checking the PCI registers if the operation was successfully.

The checking of the PCI register was added by Felix Fietkau.

Signed-off-by: Hauke Mehrtens <[email protected]>
---
 backport/backport-include/linux/pci.h | 25 +++++++++++++++++++++++++
 1 file changed, 25 insertions(+)

diff --git a/backport/backport-include/linux/pci.h b/backport/backport-include/linux/pci.h
index 84c4e8f6..1cc5f281 100644
--- a/backport/backport-include/linux/pci.h
+++ b/backport/backport-include/linux/pci.h
@@ -236,4 +236,29 @@ static inline struct pci_dev *pcie_find_root_port(struct pci_dev *dev)
 	(PCI_IRQ_LEGACY | PCI_IRQ_MSI | PCI_IRQ_MSIX)
 #endif
 
+#if defined(CONFIG_PCI)
+#if LINUX_VERSION_IS_LESS(5,3,0)
+static inline int
+backport_pci_disable_link_state(struct pci_dev *pdev, int state)
+{
+	u16 aspmc;
+
+	pci_disable_link_state(pdev, state);
+
+	pcie_capability_read_word(pdev, PCI_EXP_LNKCTL, &aspmc);
+	if ((state & PCIE_LINK_STATE_L0S) &&
+	    (aspmc & PCI_EXP_LNKCTL_ASPM_L0S))
+		return -EPERM;
+
+	if ((state & PCIE_LINK_STATE_L1) &&
+	    (aspmc & PCI_EXP_LNKCTL_ASPM_L1))
+		return -EPERM;
+
+	return 0;
+}
+#define pci_disable_link_state LINUX_BACKPORT(pci_disable_link_state)
+
+#endif /* < 5.3 */
+#endif /* defined(CONFIG_PCI) */
+
 #endif /* _BACKPORT_LINUX_PCI_H */
-- 
2.20.1

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