linux-kernel - [PATCH 1/2] PCI: Correct error reporting with PCIe failed link retraining

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Message-ID: <alpine.DEB.2.21.2402100045590.2376@angie.orcam.me.uk>
Date: Sat, 10 Feb 2024 01:43:50 +0000 (GMT)
From: "Maciej W. Rozycki" <macro@...am.me.uk>
To: Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>, 
    Bjorn Helgaas <bhelgaas@...gle.com>
cc: Mika Westerberg <mika.westerberg@...ux.intel.com>, 
    linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH 1/2] 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>
Cc: stable@...r.kernel.org # v6.5+
---
 drivers/pci/quirks.c |   18 +++++++++++-------
 1 file changed, 11 insertions(+), 7 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
@@ -74,7 +74,8 @@
  * firmware may have already arranged and lift it with ports that already
  * report their data link being up.
  *
- * Return TRUE if the link has been successfully retrained, otherwise FALSE.
+ * Return TRUE if the link has been successfully retrained, otherwise FALSE,
+ * also when retraining was not needed in the first place.
  */
 bool pcie_failed_link_retrain(struct pci_dev *dev)
 {
@@ -83,10 +84,11 @@ 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)
-		return false;
+		return ret;
 
 	pcie_capability_read_word(dev, PCI_EXP_LNKCTL2, &lnkctl2);
 	pcie_capability_read_word(dev, PCI_EXP_LNKSTA, &lnksta);
@@ -98,9 +100,10 @@ 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");
-			return false;
+			return ret;
 		}
 
 		pcie_capability_read_word(dev, PCI_EXP_LNKSTA, &lnksta);
@@ -117,13 +120,14 @@ 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 ret;
 		}
 	}
 
-	return true;
+	return ret;
 }
 
 static ktime_t fixup_debug_start(struct pci_dev *dev,