[PATCH v3] PCI: Stop waiting for link status after config read failure

[Yury Murashka <yurypm@arista.com>]

With a nested PCIe topology with multiple layers of hotplug, a link can go
down near the bottom of the topology shortly before a link above it goes
down. In that case, pcie_wait_for_link_status() can wait for the full
timeout while every read of the link status register fails because the
device has disappeared.

Return immediately when reading link status fails so event processing can
continue.

Signed-off-by: Yury Murashka <yurypm@arista.com>
Co-authored-by: James Sewart <jamessewart@arista.com>
---
 drivers/pci/pci.c | 15 +++++++++++----
 1 file changed, 10 insertions(+), 5 deletions(-)

Changes in v3:
- Check the return value of pcie_capability_read_word() and stop retrying
  when the link status read fails.
- Do not use pci_dev_is_disconnected() because a read failure does not mean
  that the device will be marked as disconnected immediately.
- Update the kernel-doc return descriptions for errors from
  pcibios_err_to_errno() while retaining the -ETIMEDOUT description.

Changes in v2:
- Check pci_dev_is_disconnected() before reading link status instead of
  checking the return value of pcie_capability_read_word().

diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
index b2879a6be5f8080e949f7abfc4bab39d791735b8..430ff08f4f4b30f12b1190ea9c5408a3a8505a5d 100644
--- a/drivers/pci/pci.c
+++ b/drivers/pci/pci.c
@@ -4565,8 +4565,9 @@ static int pci_pm_reset(struct pci_dev *dev, bool probe)
  * @use_lt: Use the LT bit if TRUE, or the DLLLA bit if FALSE.
  * @active: Waiting for active or inactive?
  *
- * Return 0 if successful, or -ETIMEDOUT if status has not changed within
- * PCIE_LINK_RETRAIN_TIMEOUT_MS milliseconds.
+ * Return: 0 if successful, -ETIMEDOUT if status has not changed within
+ * PCIE_LINK_RETRAIN_TIMEOUT_MS milliseconds, or negative error code if
+ * reading of link status failed.
  */
 static int pcie_wait_for_link_status(struct pci_dev *pdev,
 				     bool use_lt, bool active)
@@ -4574,13 +4575,16 @@ static int pcie_wait_for_link_status(struct pci_dev *pdev,
 	u16 lnksta_mask, lnksta_match;
 	unsigned long end_jiffies;
 	u16 lnksta;
+	int ret;
 
 	lnksta_mask = use_lt ? PCI_EXP_LNKSTA_LT : PCI_EXP_LNKSTA_DLLLA;
 	lnksta_match = active ? lnksta_mask : 0;
 
 	end_jiffies = jiffies + msecs_to_jiffies(PCIE_LINK_RETRAIN_TIMEOUT_MS);
 	do {
-		pcie_capability_read_word(pdev, PCI_EXP_LNKSTA, &lnksta);
+		ret = pcie_capability_read_word(pdev, PCI_EXP_LNKSTA, &lnksta);
+		if (ret)
+			return pcibios_err_to_errno(ret);
 		if ((lnksta & lnksta_mask) == lnksta_match)
 			return 0;
 		msleep(1);
@@ -4603,8 +4607,9 @@ static int pcie_wait_for_link_status(struct pci_dev *pdev,
  * according to @use_lt.  It is not verified whether the use of the DLLLA
  * bit is valid.
  *
- * Return 0 if successful, or -ETIMEDOUT if training has not completed
- * within PCIE_LINK_RETRAIN_TIMEOUT_MS milliseconds.
+ * Return: 0 if successful, -ETIMEDOUT if training has not completed within
+ * PCIE_LINK_RETRAIN_TIMEOUT_MS milliseconds, or negative error code if
+ * reading of link status failed.
  */
 int pcie_retrain_link(struct pci_dev *pdev, bool use_lt)
 {

base-commit: a500db7819c50db59e55f1b4fa1c3baa5a2616f3
-- 
2.51.0