PCI/ERR: Use slot reset if available

The secondary bus reset may have link side effects that a hotplug capable
port may incorrectly react to.  Use the slot specific reset for hotplug
ports, fixing the undesirable link down-up handling during error
recovering.

Signed-off-by: Keith Busch <keith.busch@intel.com>
[bhelgaas: fold in
https://lore.kernel.org/linux-pci/20180926152326.14821-1-keith.busch@intel.com
for issue reported by Stephen Rothwell <sfr@canb.auug.org.au>]
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Sinan Kaya <okaya@kernel.org>

drivers/pci/pci.c

@@ -35,6 +35,8 @@
 #include <linux/aer.h>
 #include "pci.h"
 
+DEFINE_MUTEX(pci_slot_mutex);
+
 const char *pci_power_names[] = {
 	"error", "D0", "D1", "D2", "D3hot", "D3cold", "unknown",
 };
@@ -5155,6 +5157,41 @@ static int pci_bus_reset(struct pci_bus *bus, int probe)
 	return ret;
 }
 
+/**
+ * pci_bus_error_reset - reset the bridge's subordinate bus
+ * @bridge: The parent device that connects to the bus to reset
+ *
+ * This function will first try to reset the slots on this bus if the method is
+ * available. If slot reset fails or is not available, this will fall back to a
+ * secondary bus reset.
+ */
+int pci_bus_error_reset(struct pci_dev *bridge)
+{
+	struct pci_bus *bus = bridge->subordinate;
+	struct pci_slot *slot;
+
+	if (!bus)
+		return -ENOTTY;
+
+	mutex_lock(&pci_slot_mutex);
+	if (list_empty(&bus->slots))
+		goto bus_reset;
+
+	list_for_each_entry(slot, &bus->slots, list)
+		if (pci_probe_reset_slot(slot))
+			goto bus_reset;
+
+	list_for_each_entry(slot, &bus->slots, list)
+		if (pci_slot_reset(slot, 0))
+			goto bus_reset;
+
+	mutex_unlock(&pci_slot_mutex);
+	return 0;
+bus_reset:
+	mutex_unlock(&pci_slot_mutex);
+	return pci_bus_reset(bridge->subordinate, 0);
+}
+
 /**
  * pci_probe_reset_bus - probe whether a PCI bus can be reset
  * @bus: PCI bus to probe