linux-kernel - [PATCH v3 3/4] PCI: Correct error reporting with PCIe failed link retraining

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Message-ID: <alpine.DEB.2.21.2408251424480.30766@angie.orcam.me.uk>
Date: Sun, 25 Aug 2024 14:47:39 +0100 (BST)
From: "Maciej W. Rozycki" <macro@...am.me.uk>
To: Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>, 
    Matthew W Carlis <mattc@...estorage.com>, 
    Bjorn Helgaas <bhelgaas@...gle.com>
cc: Mika Westerberg <mika.westerberg@...ux.intel.com>, 
    Oliver O'Halloran <oohall@...il.com>, linux-pci@...r.kernel.org, 
    linux-kernel@...r.kernel.org
Subject: [PATCH v3 3/4] 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: a89c82249c37 ("PCI: Work around PCIe link training failures")
Reported-by: Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
Link: https://lore.kernel.org/r/aa2d1c4e-9961-d54a-00c7-ddf8e858a9b0@linux.intel.com/
Signed-off-by: Maciej W. Rozycki <macro@...am.me.uk>
Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
Cc: stable@...r.kernel.org # v6.5+
---
No changes from v2.

Changes from v1 (superseding 1/2):

- Regenerate on top of 2/4.

- Reword the comment update for clarity.

- Go back to returning explicit FALSE rather than `ret' where it is known 
  that we failed.
---
 drivers/pci/quirks.c |   12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

linux-pcie-failed-link-retrain-status-fix.diff
Index: linux-macro/drivers/pci/quirks.c
===================================================================
--- linux-macro.orig/drivers/pci/quirks.c
+++ linux-macro/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
 		{}
 	};
 	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
 		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
 		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,