PCI: Consider alignment of hot-added bridges when assigning resources

Change pci_bus_distribute_available_resources() to better handle bridges
with different resource alignment requirements.

The arguments io, mmio and mmio_pref represent the start and end
addresses of resource, into which we must fit the current bridge window.

The steps taken by pci_bus_distribute_available_resources():

  - For io, mmio and mmio_pref, increase .start to align with the alignment
    of the current bridge window (otherwise the current bridge window may
    not fit within the available range).

  - For io, mmio and mmio_pref, adjust the current bridge window to the
    size after the above.

  - Count the number of hotplug bridges and normal bridges on this bus.

  - If the total number of bridges is one, give that bridge all of the
    resources and return.

  - If there are no hotplug bridges, return.

  - For io, mmio and mmio_pref, increase .start by the amount required for
    each bridge resource on the bus for non hotplug bridges, giving extra
    room to make up for alignment of those resources.

  - For io, mmio and mmio_pref, calculate the resource size per hotplug
    bridge which is available after the previous steps.

  - For io, mmio and mmio_pref, distribute the resources to each hotplug
    bridge, with the sizes calculated above.

The motivation for fixing this is enabling devices that require greater
than 1MB alignment. This fixes the case where the user hot-adds devices
with BAR alignment >1MB and Linux fails to assign resources to it.

Link: https://bugzilla.kernel.org/show_bug.cgi?id=199581
Link: https://lore.kernel.org/r/PSXP216MB0438C2BFD0FD3691ED9C83F4803C0@PSXP216MB0438.KORP216.PROD.OUTLOOK.COMReported-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Signed-off-by: Nicholas Johnson <nicholas.johnson-opensource@outlook.com.au>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Mika Westerberg <mika.westerberg@linux.intel.com>

drivers/pci/setup-bus.c

@@ -1869,17 +1869,32 @@ static void pci_bus_distribute_available_resources(struct pci_bus *bus,
 					    struct resource mmio,
 					    struct resource mmio_pref)
 {
-	resource_size_t available_io, available_mmio, available_mmio_pref;
-	resource_size_t remaining_io, remaining_mmio, remaining_mmio_pref;
 	unsigned int normal_bridges = 0, hotplug_bridges = 0;
 	struct resource *io_res, *mmio_res, *mmio_pref_res;
 	struct pci_dev *dev, *bridge = bus->self;
-	resource_size_t io_per_hp, mmio_per_hp, mmio_pref_per_hp;
+	resource_size_t io_per_hp, mmio_per_hp, mmio_pref_per_hp, align;
 
 	io_res = &bridge->resource[PCI_BRIDGE_RESOURCES + 0];
 	mmio_res = &bridge->resource[PCI_BRIDGE_RESOURCES + 1];
 	mmio_pref_res = &bridge->resource[PCI_BRIDGE_RESOURCES + 2];
 
+	/*
+	 * The alignment of this bridge is yet to be considered, hence it must
+	 * be done now before extending its bridge window.
+	 */
+	align = pci_resource_alignment(bridge, io_res);
+	if (!io_res->parent && align)
+		io.start = min(ALIGN(io.start, align), io.end + 1);
+
+	align = pci_resource_alignment(bridge, mmio_res);
+	if (!mmio_res->parent && align)
+		mmio.start = min(ALIGN(mmio.start, align), mmio.end + 1);
+
+	align = pci_resource_alignment(bridge, mmio_pref_res);
+	if (!mmio_pref_res->parent && align)
+		mmio_pref.start = min(ALIGN(mmio_pref.start, align),
+			mmio_pref.end + 1);
+
 	/*
 	 * Update additional resource list (add_list) to fill all the
 	 * extra resource space available for this port except the space
@@ -1925,12 +1940,9 @@ static void pci_bus_distribute_available_resources(struct pci_bus *bus,
 	 * extra space reduced by the minimal required space for the
 	 * non-hotplug bridges.
 	 */
-	remaining_io = available_io = resource_size(&io);
-	remaining_mmio = available_mmio = resource_size(&mmio);
-	remaining_mmio_pref = available_mmio_pref = resource_size(&mmio_pref);
-
 	for_each_pci_bridge(dev, bus) {
-		const struct resource *res;
+		resource_size_t used_size;
+		struct resource *res;
 
 		if (dev->is_hotplug_bridge)
 			continue;
@@ -1940,24 +1952,39 @@ static void pci_bus_distribute_available_resources(struct pci_bus *bus,
 		 * bridge and devices below it occupy.
 		 */
 		res = &dev->resource[PCI_BRIDGE_RESOURCES + 0];
-		if (!res->parent && available_io > resource_size(res))
-			remaining_io -= resource_size(res);
+		align = pci_resource_alignment(dev, res);
+		align = align ? ALIGN(io.start, align) - io.start : 0;
+		used_size = align + resource_size(res);
+		if (!res->parent)
+			io.start = min(io.start + used_size, io.end + 1);
 
 		res = &dev->resource[PCI_BRIDGE_RESOURCES + 1];
-		if (!res->parent && available_mmio > resource_size(res))
-			remaining_mmio -= resource_size(res);
+		align = pci_resource_alignment(dev, res);
+		align = align ? ALIGN(mmio.start, align) - mmio.start : 0;
+		used_size = align + resource_size(res);
+		if (!res->parent)
+			mmio.start = min(mmio.start + used_size, mmio.end + 1);
 
 		res = &dev->resource[PCI_BRIDGE_RESOURCES + 2];
-		if (!res->parent && available_mmio_pref > resource_size(res))
-			remaining_mmio_pref -= resource_size(res);
+		align = pci_resource_alignment(dev, res);
+		align = align ? ALIGN(mmio_pref.start, align) -
+			mmio_pref.start : 0;
+		used_size = align + resource_size(res);
+		if (!res->parent)
+			mmio_pref.start = min(mmio_pref.start + used_size,
+				mmio_pref.end + 1);
 	}
 
+	io_per_hp = div64_ul(resource_size(&io), hotplug_bridges);
+	mmio_per_hp = div64_ul(resource_size(&mmio), hotplug_bridges);
+	mmio_pref_per_hp = div64_ul(resource_size(&mmio_pref),
+		hotplug_bridges);
+
 	/*
 	 * Go over devices on this bus and distribute the remaining
 	 * resource space between hotplug bridges.
 	 */
 	for_each_pci_bridge(dev, bus) {
-		resource_size_t align;
 		struct pci_bus *b;
 
 		b = dev->subordinate;
@@ -1969,29 +1996,16 @@ static void pci_bus_distribute_available_resources(struct pci_bus *bus,
 		 * hotplug-capable downstream ports taking alignment into
 		 * account.
 		 */
-		align = pci_resource_alignment(bridge, io_res);
-		io_per_hp = div64_ul(available_io, hotplug_bridges);
-		io_per_hp = min(ALIGN(io_per_hp, align), remaining_io);
-		remaining_io -= io_per_hp;
-
-		align = pci_resource_alignment(bridge, mmio_res);
-		mmio_per_hp = div64_ul(available_mmio, hotplug_bridges);
-		mmio_per_hp = min(ALIGN(mmio_per_hp, align), remaining_mmio);
-		remaining_mmio -= mmio_per_hp;
-
-		align = pci_resource_alignment(bridge, mmio_pref_res);
-		mmio_pref_per_hp = div64_ul(available_mmio_pref,
-					    hotplug_bridges);
-		mmio_pref_per_hp = min(ALIGN(mmio_pref_per_hp, align),
-				       remaining_mmio_pref);
-		remaining_mmio_pref -= mmio_pref_per_hp;
-
 		io.end = io.start + io_per_hp - 1;
 		mmio.end = mmio.start + mmio_per_hp - 1;
 		mmio_pref.end = mmio_pref.start + mmio_pref_per_hp - 1;
 
 		pci_bus_distribute_available_resources(b, add_list, io, mmio,
 						       mmio_pref);
+
+		io.start += io_per_hp;
+		mmio.start += mmio_per_hp;
+		mmio_pref.start += mmio_pref_per_hp;
 	}
 }