[PATCH v7 6/8] PCI: Allow extend_bridge_window() to shrink resource if necessary

[Nicholas Johnson]

Remove checks for resource size in extend_bridge_window(). This is
necessary to allow the pci_bus_distribute_available_resources() to
function when the kernel parameter pci=hpmemsize=nn[KMG] is used to
allocate resources. Because the kernel parameter sets the size of all
hotplug bridges to be the same, there are problems when nested hotplug
bridges are encountered. Fitting a downstream hotplug bridge with size X
and normal bridges with size Y into parent hotplug bridge with size X is
impossible, and hence the downstream hotplug bridge needs to shrink to
fit into its parent.

Add check for if bridge is extended or shrunken and adjust pci_dbg to
reflect this.

Reset the resource if its new size is zero (if we have run out of a
bridge window resource). If it is set to zero size and left, it can
cause significant problems when it comes to enabling devices.

Signed-off-by: Nicholas Johnson <nicholas.johnson-opensource@xxxxxxxxxxxxxx>
---
 drivers/pci/setup-bus.c | 16 +++++++++++-----
 1 file changed, 11 insertions(+), 5 deletions(-)

diff --git a/drivers/pci/setup-bus.c b/drivers/pci/setup-bus.c
index d65982438..9064fd964 100644
--- a/drivers/pci/setup-bus.c
+++ b/drivers/pci/setup-bus.c
@@ -1818,13 +1818,19 @@ static void extend_bridge_window(struct pci_dev *bridge, struct resource *res,
 	if (res->parent)
 		return;
 
-	if (resource_size(res) >= new_size)
-		return;
-
-	add_size = new_size - resource_size(res);
-	pci_dbg(bridge, "bridge window %pR extended by %pa\n", res, &add_size);
+	if (new_size > resource_size(res)) {
+		add_size = new_size - resource_size(res);
+		pci_dbg(bridge, "bridge window %pR extended by %pa\n", res,
+			&add_size);
+	} else if (new_size < resource_size(res)) {
+		add_size = resource_size(res) - new_size;
+		pci_dbg(bridge, "bridge window %pR shrunken by %pa\n", res,
+			&add_size);
+	}
 	res->end = res->start + new_size - 1;
 	remove_from_list(add_list, res);
+	if (!new_size)
+		reset_resource(res);
 }
 
 static void pci_bus_distribute_available_resources(struct pci_bus *bus,
-- 
2.20.1