[SeaBIOS] [PATCH v3 1/2] pci: reserve resources for pcie-pci-bridge to fix regressed hotplug on q35

[Igor Mammedov]

If QEMU is started with unpopulated pcie-pci-bridge with ACPI PCI
hotplug enabled (default since QEMU-6.1), hotplugging a PCI device
into one of the bridge slots fails due to lack of resources.

once linux guest is booted (test used Fedora 34), hotplug NIC from
QEMU monitor:
  (qemu) device_add rtl8139,bus=pcie-pci-bridge-0,addr=0x2

guest fails hotplug with:
  pci 0000:01:02.0: [10ec:8139] type 00 class 0x020000
  pci 0000:01:02.0: reg 0x10: [io  0x0000-0x00ff]
  pci 0000:01:02.0: reg 0x14: [mem 0x00000000-0x000000ff]
  pci 0000:01:02.0: reg 0x30: [mem 0x00000000-0x0003ffff pref]
  pci 0000:01:02.0: BAR 6: no space for [mem size 0x00040000 pref]
  pci 0000:01:02.0: BAR 6: failed to assign [mem size 0x00040000 pref]
  pci 0000:01:02.0: BAR 0: no space for [io  size 0x0100]
  pci 0000:01:02.0: BAR 0: failed to assign [io  size 0x0100]
  pci 0000:01:02.0: BAR 1: no space for [mem size 0x00000100]
  pci 0000:01:02.0: BAR 1: failed to assign [mem size 0x00000100]
  8139cp: 8139cp: 10/100 PCI Ethernet driver v1.3 (Mar 22, 2004)
  PCI Interrupt Link [GSIG] enabled at IRQ 22
  8139cp 0000:01:02.0: no MMIO resource
  8139cp: probe of 0000:01:02.0 failed with error -5

Reason for this is that commit [1] didn't take into account
pcie-pci-bridge, marking bridge as non hotpluggable instead of
handling it as possibly SHPC capable bridge.
Fix issue by checking if pcie-pci-bridge is SHPC capable and
if it is mark it as hotpluggable.

Fixes regression in QEMU-6.1 and later, since it was switched
to ACPI based PCI hotplug on Q35 by default at that time.

RHBZ: https://bugzilla.redhat.com/show_bug.cgi?id=2001732
[1]
Fixes: 3aa31d7d637 ("hw/pci: reserve IO and mem for pci express downstream ports with no devices attached")
Signed-off-by: Igor Mammedov [e-mail]
CC: [e-mail]
CC: [e-mail]
CC: [e-mail]
CC: [e-mail]
CC: [e-mail]
---
 src/fw/pciinit.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/src/fw/pciinit.c b/src/fw/pciinit.c
index d25931bb..7342d8d8 100644
--- a/src/fw/pciinit.c
+++ b/src/fw/pciinit.c
@@ -802,6 +802,10 @@ static int pci_bus_hotplug_support(struct pci_bus *bus, u8 pcie_cap)
                                           pcie_cap + PCI_EXP_FLAGS);
         u8 port_type = ((pcie_flags & PCI_EXP_FLAGS_TYPE) >>
                        (__builtin_ffs(PCI_EXP_FLAGS_TYPE) - 1));
+
+        if (port_type == PCI_EXP_TYPE_PCI_BRIDGE)
+            goto check_shpc;
+
         u8 downstream_port = (port_type == PCI_EXP_TYPE_DOWNSTREAM) ||
                              (port_type == PCI_EXP_TYPE_ROOT_PORT);
         /*
@@ -818,6 +822,7 @@ static int pci_bus_hotplug_support(struct pci_bus *bus, u8 pcie_cap)
         return downstream_port && slot_implemented;
     }

+check_shpc:
     shpc_cap = pci_find_capability(bus->bus_dev->bdf, PCI_CAP_ID_SHPC, 0);
     return !!shpc_cap;
 }