[PATCH v1 4/4] PCI: Allow extend_bridge_window() to shrink resource if necessary

[Nicholas Johnson <nicholas.johnson-opensource@outlook.com.au>]

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 non-zero 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 reflect that in the
call to pci_dbg().

Reset the resource if its new size is zero (if we have run out of a
bridge window resource) to prevent the PCI resource assignment code from
attempting to assign a zero-sized resource.

Signed-off-by: Nicholas Johnson <nicholas.johnson-opensource@outlook.com.au>
---
 drivers/pci/setup-bus.c | 17 ++++++++++++-----
 1 file changed, 12 insertions(+), 5 deletions(-)

diff --git a/drivers/pci/setup-bus.c b/drivers/pci/setup-bus.c
index 0c51f4937..e7e57bf72 100644
--- a/drivers/pci/setup-bus.c
+++ b/drivers/pci/setup-bus.c
@@ -1836,18 +1836,25 @@ static void adjust_bridge_window(struct pci_dev *bridge, struct resource *res,
 				 struct list_head *add_list,
 				 resource_size_t new_size)
 {
-	resource_size_t add_size;
+	resource_size_t add_size, size = resource_size(res);
 
 	if (res->parent)
 		return;
 
-	if (resource_size(res) >= new_size)
-		return;
+	if (new_size > size) {
+		add_size = new_size - size;
+		pci_dbg(bridge, "bridge window %pR extended by %pa\n", res,
+			&add_size);
+	} else if (new_size < size) {
+		add_size = size - new_size;
+		pci_dbg(bridge, "bridge window %pR shrunken by %pa\n", res,
+			&add_size);
+	}
 
-	add_size = new_size - resource_size(res);
-	pci_dbg(bridge, "bridge window %pR extended 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,
-- 
2.24.1