PCI: Correct error reporting with PCIe failed link retraining

Only return successful completion status from pcie_failed_link_retrain() if
retraining has actually been done, preventing excessive delays from being
triggered at call sites in a hope that communication will finally be
established with the downstream device where in fact nothing has been done
about the link in question that would justify such a hope.

Fixes: a89c822 ("PCI: Work around PCIe link training failures")
Link: https://lore.kernel.org/r/[email protected]
Reported-by: Ilpo Järvinen <[email protected]>
Link: https://lore.kernel.org/r/[email protected]/
Signed-off-by: Maciej W. Rozycki <[email protected]>
Signed-off-by: Bjorn Helgaas <[email protected]>
Signed-off-by: Krzysztof Wilczyński <[email protected]>
Reviewed-by: Ilpo Järvinen <[email protected]>
Cc: <[email protected]> # v6.5+

drivers/pci/quirks.c

@@ -78,7 +78,8 @@
  * again to remove any residual state, ignoring the result as it's supposed
  * to fail anyway.
  *
- * Return TRUE if the link has been successfully retrained, otherwise FALSE.
+ * Return TRUE if the link has been successfully retrained.  Return FALSE
+ * if retraining was not needed or we attempted a retrain and it failed.
  */
 bool pcie_failed_link_retrain(struct pci_dev *dev)
 {
@@ -87,6 +88,7 @@ bool pcie_failed_link_retrain(struct pci_dev *dev)
 		{}
 	};
 	u16 lnksta, lnkctl2;
+	bool ret = false;
 
 	if (!pci_is_pcie(dev) || !pcie_downstream_port(dev) ||
 	    !pcie_cap_has_lnkctl2(dev) || !dev->link_active_reporting)
@@ -104,7 +106,8 @@ bool pcie_failed_link_retrain(struct pci_dev *dev)
 		lnkctl2 |= PCI_EXP_LNKCTL2_TLS_2_5GT;
 		pcie_capability_write_word(dev, PCI_EXP_LNKCTL2, lnkctl2);
 
-		if (pcie_retrain_link(dev, false)) {
+		ret = pcie_retrain_link(dev, false) == 0;
+		if (!ret) {
 			pci_info(dev, "retraining failed\n");
 			pcie_capability_write_word(dev, PCI_EXP_LNKCTL2,
 						   oldlnkctl2);
@@ -126,13 +129,14 @@ bool pcie_failed_link_retrain(struct pci_dev *dev)
 		lnkctl2 |= lnkcap & PCI_EXP_LNKCAP_SLS;
 		pcie_capability_write_word(dev, PCI_EXP_LNKCTL2, lnkctl2);
 
-		if (pcie_retrain_link(dev, false)) {
+		ret = pcie_retrain_link(dev, false) == 0;
+		if (!ret) {
 			pci_info(dev, "retraining failed\n");
 			return false;
 		}
 	}
 
-	return true;
+	return ret;
 }
 
 static ktime_t fixup_debug_start(struct pci_dev *dev,