[PATCH v12 4/4] PCI: Allow extend_bridge_window() to shrink resource if necessary

From: Nicholas Johnson
Date: Mon Dec 09 2019 - 08:00:59 EST

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>
Reviewed-by: Mika Westerberg <mika.westerberg@xxxxxxxxxxxxxxx>
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 0e0c8b677..22aed6cdb 100644
--- a/drivers/pci/setup-bus.c
+++ b/drivers/pci/setup-bus.c
@@ -1832,22 +1832,29 @@ 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)

- 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,
@@ -1883,9 +1890,9 @@ 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, whilst 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,