[PATCH v10 4/4] 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 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 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) to prevent the PCI resource assignment code from
attempting to assign a zero-sized resource.

Rename extend_bridge_window() to adjust_bridge_window() to reflect the
fact that the window can now shrink.

Signed-off-by: Nicholas Johnson <nicholas.johnson-opensource@xxxxxxxxxxxxxx>
---
 drivers/pci/setup-bus.c | 25 ++++++++++++++++---------
 1 file changed, 16 insertions(+), 9 deletions(-)

diff --git a/drivers/pci/setup-bus.c b/drivers/pci/setup-bus.c
index d83c55169..6b64bf909 100644
--- a/drivers/pci/setup-bus.c
+++ b/drivers/pci/setup-bus.c
@@ -1814,22 +1814,29 @@ void __init pci_assign_unassigned_resources(void)
 	}
 }
 
-static void extend_bridge_window(struct pci_dev *bridge, struct resource *res,
+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,
@@ -1865,9 +1872,9 @@ static void pci_bus_distribute_available_resources(struct pci_bus *bus,
 	 * Update the resources to fill as much remaining resource space in the
 	 * parent bridge as possible, while considering alignment.
 	 */
-	extend_bridge_window(bridge, io_res, add_list, resource_size(&io));
-	extend_bridge_window(bridge, mmio_res, add_list, resource_size(&mmio));
-	extend_bridge_window(bridge, mmio_pref_res, add_list,
+	adjust_bridge_window(bridge, io_res, add_list, resource_size(&io));
+	adjust_bridge_window(bridge, mmio_res, add_list, resource_size(&mmio));
+	adjust_bridge_window(bridge, mmio_pref_res, add_list,
 			     resource_size(&mmio_pref));
 
 	/*
-- 
2.23.0