From 4147c2fd9b12ae1e0bdbb2dbb9a9163c94a10a22 Mon Sep 17 00:00:00 2001
From: Mika Westerberg <mika.westerberg@linux.intel.com>
Date: Fri, 13 Oct 2017 21:35:42 +0300
Subject: [PATCH] PCI: Open-code the two pass loop when scanning bridges
Git-commit: 4147c2fd9b12ae1e0bdbb2dbb9a9163c94a10a22
Patch-mainline: v4.15-rc1
References: bsc#1070681

The current scanning code is really hard to understand because it calls
the same function in a loop where pass value is changed without any
comments explaining it:

  for (pass = 0; pass < 2; pass++)
    for_each_pci_bridge(dev, bus)
      max = pci_scan_bridge(bus, dev, max, pass);

Unfamiliar reader cannot tell easily what is the purpose of this loop
without looking at internals of pci_scan_bridge().

In order to make this bit easier to understand, open-code the loop in
pci_scan_child_bus() and pci_hp_add_bridge() with added comments.

No functional changes intended.

Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Signed-off-by: Oliver Neukum <oneukum@suse.com>
---
 drivers/pci/probe.c |   27 ++++++++++++++++++++-------
 1 file changed, 20 insertions(+), 7 deletions(-)

--- a/drivers/pci/probe.c
+++ b/drivers/pci/probe.c
@@ -2306,7 +2306,7 @@ EXPORT_SYMBOL_GPL(pcie_bus_configure_set
 
 unsigned int pci_scan_child_bus(struct pci_bus *bus)
 {
-	unsigned int devfn, pass, max = bus->busn_res.start;
+	unsigned int devfn, max = bus->busn_res.start;
 	struct pci_dev *dev;
 
 	dev_dbg(&bus->dev, "scanning bus\n");
@@ -2328,9 +2328,17 @@ unsigned int pci_scan_child_bus(struct p
 		bus->is_added = 1;
 	}
 
-	for (pass = 0; pass < 2; pass++)
-		for_each_pci_bridge(dev, bus)
-			max = pci_scan_bridge(bus, dev, max, pass);
+	/*
+	 * Scan bridges that are already configured. We don't touch them
+	 * unless they are misconfigured (which will be done in the second
+	 * scan below).
+	 */
+	for_each_pci_bridge(dev, bus)
+		max = pci_scan_bridge(bus, dev, max, 0);
+
+	/* Scan bridges that need to be reconfigured */
+	for_each_pci_bridge(dev, bus)
+		max = pci_scan_bridge(bus, dev, max, 1);
 
 	/*
 	 * Make sure a hotplug bridge has at least the minimum requested
@@ -2626,7 +2634,7 @@ void __init pci_sort_breadthfirst(void)
 int pci_hp_add_bridge(struct pci_dev *dev)
 {
 	struct pci_bus *parent = dev->bus;
-	int pass, busnr, start = parent->busn_res.start;
+	int busnr, start = parent->busn_res.start;
 	int end = parent->busn_res.end;
 
 	for (busnr = start; busnr <= end; busnr++) {
@@ -2637,8 +2645,13 @@ int pci_hp_add_bridge(struct pci_dev *de
 		dev_err(&dev->dev, "No bus number available for hot-added bridge\n");
 		return -1;
 	}
-	for (pass = 0; pass < 2; pass++)
-		busnr = pci_scan_bridge(parent, dev, busnr, pass);
+
+	/* Scan bridges that are already configured */
+	busnr = pci_scan_bridge(parent, dev, busnr, 0);
+
+	/* Scan bridges that need to be reconfigured */
+	pci_scan_bridge(parent, dev, busnr, 1);
+
 	if (!dev->subordinate)
 		return -1;