hw/pcie: fix Extended Configuration Space for devices with no Extended Capabilities

Absence of any Extended Capabilities is required to be
indicated by an Extended Capability header with a Capability ID of
0000h, a Capability Version of 0h, and a Next Capability Offset of 000h.

Instead of inserting a 'NULL' capability is simpler to mark the start
of the Extended Configuration Space as read-only to achieve the same
behaviour.

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

hw/pci/pci.c

@@ -64,6 +64,8 @@ static Property pci_props[] = {
                     QEMU_PCI_CAP_SERR_BITNR, true),
     DEFINE_PROP_BIT("x-pcie-lnksta-dllla", PCIDevice, cap_present,
                     QEMU_PCIE_LNKSTA_DLLLA_BITNR, true),
+    DEFINE_PROP_BIT("x-pcie-extcap-init", PCIDevice, cap_present,
+                    QEMU_PCIE_EXTCAP_INIT_BITNR, true),
     DEFINE_PROP_END_OF_LIST()
 };
 

hw/pci/pcie.c

@@ -109,6 +109,12 @@ int pcie_cap_init(PCIDevice *dev, uint8_t offset, uint8_t type, uint8_t port)
                  PCI_EXP_DEVCAP2_EFF | PCI_EXP_DEVCAP2_EETLPP);
 
     pci_set_word(dev->wmask + pos + PCI_EXP_DEVCTL2, PCI_EXP_DEVCTL2_EETLPPB);
+
+    if (dev->cap_present & QEMU_PCIE_EXTCAP_INIT) {
+        /* read-only to behave like a 'NULL' Extended Capability Header */
+        pci_set_long(dev->wmask + PCI_CONFIG_SPACE_SIZE, 0);
+    }
+
     return pos;
 }
 

include/hw/compat.h

@@ -18,6 +18,10 @@
         .driver   = "pci-bridge",\
         .property = "shpc",\
         .value    = "on",\
+    },{\
+        .driver   = TYPE_PCI_DEVICE,\
+        .property = "x-pcie-extcap-init",\
+        .value    = "off",\
     },
 
 #define HW_COMPAT_2_7 \

include/hw/pci/pci.h

@@ -183,6 +183,8 @@ enum {
     /* Link active status in endpoint capability is always set */
 #define QEMU_PCIE_LNKSTA_DLLLA_BITNR 8
     QEMU_PCIE_LNKSTA_DLLLA = (1 << QEMU_PCIE_LNKSTA_DLLLA_BITNR),
+#define QEMU_PCIE_EXTCAP_INIT_BITNR 9
+    QEMU_PCIE_EXTCAP_INIT = (1 << QEMU_PCIE_EXTCAP_INIT_BITNR),
 };
 
 #define TYPE_PCI_DEVICE "pci-device"