[PATCH v3 1/2] PCI: Take other bus devices into account when distributing resources

[Mika Westerberg <mika.westerberg@linux.intel.com>]

A PCI bridge may reside on a bus with other devices as well. The
resource distribution code does not take this into account properly and
therefore it expands the bridge resource windows too much, not leaving
space for the other devices (or functions a multifunction device) and
this leads to an issue that Jonathan reported. He runs QEMU with the
following topoology (QEMU parameters):

 -device pcie-root-port,port=0,id=root_port13,chassis=0,slot=2	\
 -device x3130-upstream,id=sw1,bus=root_port13,multifunction=on	\
 -device e1000,bus=root_port13,addr=0.1 			\
 -device xio3130-downstream,id=fun1,bus=sw1,chassis=0,slot=3	\
 -device e1000,bus=fun1

The first e1000 NIC here is another function in the switch upstream
port. This leads to following errors:

  pci 0000:00:04.0: bridge window [mem 0x10200000-0x103fffff] to [bus 02-04]
  pci 0000:02:00.0: bridge window [mem 0x10200000-0x103fffff] to [bus 03-04]
  pci 0000:02:00.1: BAR 0: failed to assign [mem size 0x00020000]
  e1000 0000:02:00.1: can't ioremap BAR 0: [??? 0x00000000 flags 0x0]

Fix this by taking into account the possible multifunction devices when
uptream port resources are distributed.

Link: https://lore.kernel.org/linux-pci/20221014124553.0000696f@huawei.com/
Reported-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>
---
 drivers/pci/setup-bus.c | 66 ++++++++++++++++++++++++++++++++++++++---
 1 file changed, 62 insertions(+), 4 deletions(-)

diff --git a/drivers/pci/setup-bus.c b/drivers/pci/setup-bus.c
index b4096598dbcb..d456175ddc4f 100644
--- a/drivers/pci/setup-bus.c
+++ b/drivers/pci/setup-bus.c
@@ -1830,10 +1830,68 @@ static void pci_bus_distribute_available_resources(struct pci_bus *bus,
 	 * bridges below.
 	 */
 	if (hotplug_bridges + normal_bridges == 1) {
-		dev = list_first_entry(&bus->devices, struct pci_dev, bus_list);
-		if (dev->subordinate)
-			pci_bus_distribute_available_resources(dev->subordinate,
-				add_list, io, mmio, mmio_pref);
+		bridge = NULL;
+
+		/* Find the single bridge on this bus first */
+		for_each_pci_bridge(dev, bus) {
+			bridge = dev;
+			break;
+		}
+
+		if (WARN_ON_ONCE(!bridge))
+			return;
+		if (!bridge->subordinate)
+			return;
+
+		/*
+		 * Reduce the space available for distribution by the
+		 * amount required by the other devices on the same bus
+		 * as this bridge.
+		 */
+		list_for_each_entry(dev, &bus->devices, bus_list) {
+			int i;
+
+			if (dev == bridge)
+				continue;
+
+			for (i = 0; i < PCI_NUM_RESOURCES; i++) {
+				const struct resource *dev_res = &dev->resource[i];
+				resource_size_t dev_sz;
+				struct resource *b_res;
+
+				if (dev_res->flags & IORESOURCE_IO) {
+					b_res = &io;
+				} else if (dev_res->flags & IORESOURCE_MEM) {
+					if (dev_res->flags & IORESOURCE_PREFETCH)
+						b_res = &mmio_pref;
+					else
+						b_res = &mmio;
+				} else {
+					continue;
+				}
+
+				/* Size aligned to bridge window */
+				align = pci_resource_alignment(bridge, b_res);
+				dev_sz = ALIGN(resource_size(dev_res), align);
+				if (!dev_sz)
+					continue;
+
+				pci_dbg(dev, "resource %pR aligned to %#llx\n",
+					dev_res, (unsigned long long)dev_sz);
+
+				if (dev_sz > resource_size(b_res))
+					memset(b_res, 0, sizeof(*b_res));
+				else
+					b_res->end -= dev_sz;
+
+				pci_dbg(bridge, "updated available resources to %pR\n",
+					b_res);
+			}
+		}
+
+		pci_bus_distribute_available_resources(bridge->subordinate,
+						       add_list, io, mmio,
+						       mmio_pref);
 		return;
 	}
 
-- 
2.35.1