powerpc/pci/of: Parse unassigned resources

BugLink: https://bugs.launchpad.net/bugs/1878232

commit dead1c84 upstream.

The pseries platform uses the PCI_PROBE_DEVTREE method of PCI probing
which reads "assigned-addresses" of every PCI device and initializes
the device resources. However if the property is missing or zero sized,
then there is no fallback of any kind and the PCI resources remain
undiscovered, i.e. pdev->resource[] array remains empty.

This adds a fallback which parses the "reg" property in pretty much same
way except it marks resources as "unset" which later make Linux assign
those resources proper addresses.

This has an effect when:
1. a hypervisor failed to assign any resource for a device;
2. /chosen/linux,pci-probe-only=0 is in the DT so the system may try
assigning a resource.
Neither is likely to happen under PowerVM.
Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Cc: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Ian May <ian.may@canonical.com>
Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>

arch/powerpc/kernel/pci_of_scan.c

@@ -82,10 +82,16 @@ static void of_pci_parse_addrs(struct device_node *node, struct pci_dev *dev)
 	const __be32 *addrs;
 	u32 i;
 	int proplen;
+	bool mark_unset = false;
 
 	addrs = of_get_property(node, "assigned-addresses", &proplen);
-	if (!addrs)
-		return;
+	if (!addrs || !proplen) {
+		addrs = of_get_property(node, "reg", &proplen);
+		if (!addrs || !proplen)
+			return;
+		mark_unset = true;
+	}
+
 	pr_debug("    parse addresses (%d bytes) @ %p\n", proplen, addrs);
 	for (; proplen >= 20; proplen -= 20, addrs += 5) {
 		flags = pci_parse_of_flags(of_read_number(addrs, 1), 0);
@@ -110,6 +116,8 @@ static void of_pci_parse_addrs(struct device_node *node, struct pci_dev *dev)
 			continue;
 		}
 		res->flags = flags;
+		if (mark_unset)
+			res->flags |= IORESOURCE_UNSET;
 		res->name = pci_name(dev);
 		region.start = base;
 		region.end = base + size - 1;