[PATCH v9 13/14] PCI: Add failed link recovery for device reset events

[Maciej W. Rozycki]

Request failed link recovery with any upstream bridge where a device has 
not come back after reset within PCI_RESET_WAIT time.  Reset the polling 
interval if recovery succeeded, otherwise continue as usual.

Signed-off-by: Maciej W. Rozycki <macro at orcam.me.uk>
---
New change in v9, factored out from 7/7:

- Remove duplicate succesful completion report previously added (not sure 
  where it came from, possibly an unnoticed leftover from experiments).

- Make the type of `retrain' variable `bool' rather than `int' and invert
  the logic used.

- Rename `pcie_downstream_link_retrain' to `pcie_failed_link_retrain'.

- Rename `pcie_upstream_link_retrain' to `pcie_parent_link_retrain'.  Add 
  documentation.
---
 drivers/pci/pci.c |   39 ++++++++++++++++++++++++++++++++++-----
 1 file changed, 34 insertions(+), 5 deletions(-)

linux-pcie-dev-wait-link-retrain.diff
Index: linux-macro/drivers/pci/pci.c
===================================================================
--- linux-macro.orig/drivers/pci/pci.c
+++ linux-macro/drivers/pci/pci.c
@@ -1146,10 +1146,27 @@ void pci_resume_bus(struct pci_bus *bus)
 		pci_walk_bus(bus, pci_resume_one, NULL);
 }
 
+/**
+ * pcie_parent_link_retrain - Check and retrain link we are downstream from
+ * @dev: PCI device to handle.
+ *
+ * Return TRUE if the link was retrained, FALSE otherwise.
+ */
+static bool pcie_parent_link_retrain(struct pci_dev *dev)
+{
+	struct pci_dev *bridge;
+
+	bridge = pci_upstream_bridge(dev);
+	if (bridge)
+		return pcie_failed_link_retrain(bridge);
+	else
+		return false;
+}
+
 static int pci_dev_wait(struct pci_dev *dev, char *reset_type, int timeout)
 {
+	bool retrain = true;
 	int delay = 1;
-	u32 id;
 
 	/*
 	 * After reset, the device should not silently discard config
@@ -1163,21 +1180,33 @@ static int pci_dev_wait(struct pci_dev *
 	 * Command register instead of Vendor ID so we don't have to
 	 * contend with the CRS SV value.
 	 */
-	pci_read_config_dword(dev, PCI_COMMAND, &id);
-	while (PCI_POSSIBLE_ERROR(id)) {
+	for (;;) {
+		u32 id;
+
+		pci_read_config_dword(dev, PCI_COMMAND, &id);
+		if (!PCI_POSSIBLE_ERROR(id))
+			break;
+
 		if (delay > timeout) {
 			pci_warn(dev, "not ready %dms after %s; giving up\n",
 				 delay - 1, reset_type);
 			return -ENOTTY;
 		}
 
-		if (delay > PCI_RESET_WAIT)
+		if (delay > PCI_RESET_WAIT) {
+			if (retrain) {
+				retrain = false;
+				if (pcie_parent_link_retrain(dev)) {
+					delay = 1;
+					continue;
+				}
+			}
 			pci_info(dev, "not ready %dms after %s; waiting\n",
 				 delay - 1, reset_type);
+		}
 
 		msleep(delay);
 		delay *= 2;
-		pci_read_config_dword(dev, PCI_COMMAND, &id);
 	}
 
 	if (delay > PCI_RESET_WAIT)