Currently we only emit trace events for existing PCI functions.
In order to ease debugging PCI enumeration process, also emit
for unexisting functions:

  $ qemu-system-foo -trace pci_cfg_\*
  ...
  pci_cfg_read empty 00:0a.4 @0x0 -> 0xffffffff
  pci_cfg_read empty 00:0a.5 @0x0 -> 0xffffffff
  pci_cfg_read empty 00:0a.6 @0x0 -> 0xffffffff
  pci_cfg_read empty 00:0a.7 @0x0 -> 0xffffffff
  pci_cfg_read pcnet 00:0b.0 @0x0 -> 0x20001022
  pci_cfg_read empty 00:0c.0 @0x0 -> 0xffffffff
  pci_cfg_read empty 00:0d.0 @0x0 -> 0xffffffff
  pci_cfg_read empty 00:0e.0 @0x0 -> 0xffffffff
  pci_cfg_read empty 00:0f.0 @0x0 -> 0xffffffff
  pci_cfg_read empty 00:10.0 @0x0 -> 0xffffffff
  pci_cfg_read empty 00:11.0 @0x0 -> 0xffffffff
  pci_cfg_read cirrus-vga 00:12.0 @0x0 -> 0xb81013

Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
---
 hw/pci/pci_host.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/hw/pci/pci_host.c b/hw/pci/pci_host.c
index eaf217ff55..ead1d3e61c 100644
--- a/hw/pci/pci_host.c
+++ b/hw/pci/pci_host.c
@@ -118,6 +118,9 @@ void pci_data_write(PCIBus *s, uint32_t addr, uint32_t val, unsigned len)
     uint32_t config_addr = addr & (PCI_CONFIG_SPACE_SIZE - 1);
 
     if (!pci_dev) {
+        trace_pci_cfg_write("empty", extract32(addr, 16, 8),
+                            extract32(addr, 11, 5), extract32(addr, 8, 3),
+                            config_addr, val);
         return;
     }
 
@@ -131,6 +134,9 @@ uint32_t pci_data_read(PCIBus *s, uint32_t addr, unsigned len)
     uint32_t config_addr = addr & (PCI_CONFIG_SPACE_SIZE - 1);
 
     if (!pci_dev) {
+        trace_pci_cfg_read("empty", extract32(addr, 16, 8),
+                           extract32(addr, 11, 5), extract32(addr, 8, 3),
+                           config_addr, ~0x0);
         return ~0x0;
     }
 
-- 
2.38.1