fw/pci: do not automatically allocate IO region for PCIe bridges

PCIe downstream ports (Root Ports and switches Downstream Ports) appear
to firmware as PCI-PCI bridges and a 4K IO space is allocated for them
even if there is no device behind them requesting IO space,
all that for hotplug purpose.

However, PCIe devices can work without IO, so there is no need
to allocate IO space for hotplug.

Acked-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Marcel Apfelbaum <marcel@redhat.com>

diff --git a/src/fw/pciinit.c b/src/fw/pciinit.c
index 7b8aab7c487ea38e4caaf2afbacc592df02d9bc1..c31c2fa0cd1999018ed388288feeb4dcf0e290a0 100644 (file)
--- a/src/fw/pciinit.c
+++ b/src/fw/pciinit.c
@@ -645,9 +645,8 @@ pci_region_create_entry(struct pci_bus *bus, struct pci_device *dev,
     return entry;
 }
 
-static int pci_bus_hotplug_support(struct pci_bus *bus)
+static int pci_bus_hotplug_support(struct pci_bus *bus, u8 pcie_cap)
 {
-    u8 pcie_cap = pci_find_capability(bus->bus_dev, PCI_CAP_ID_EXP, 0);
     u8 shpc_cap;
 
     if (pcie_cap) {
@@ -727,7 +726,8 @@ static int pci_bios_check_devices(struct pci_bus *busses)
              */
             parent = &busses[0];
         int type;
-        int hotplug_support = pci_bus_hotplug_support(s);
+        u8 pcie_cap = pci_find_capability(s->bus_dev, PCI_CAP_ID_EXP, 0);
+        int hotplug_support = pci_bus_hotplug_support(s, pcie_cap);
         for (type = 0; type < PCI_REGION_TYPE_COUNT; type++) {
             u64 align = (type == PCI_REGION_TYPE_IO) ?
                 PCI_BRIDGE_IO_MIN : PCI_BRIDGE_MEM_MIN;
@@ -736,7 +736,8 @@ static int pci_bios_check_devices(struct pci_bus *busses)
             if (pci_region_align(&s->r[type]) > align)
                  align = pci_region_align(&s->r[type]);
             u64 sum = pci_region_sum(&s->r[type]);
-            if (!sum && hotplug_support)
+            int resource_optional = pcie_cap && (type == PCI_REGION_TYPE_IO);
+            if (!sum && hotplug_support && !resource_optional)
                 sum = align; /* reserve min size for hot-plug */
             u64 size = ALIGN(sum, align);
             int is64 = pci_bios_bridge_region_is64(&s->r[type],