pci-ids: document modern virtio-pci ids in pci.h too

While being at it add a #define for the magic 0x1040 number.

Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Reviewed-by: Eric Auger <eric.auger@redhat.com>
Message-Id: <20221004112100.301935-6-kraxel@redhat.com>

hw/virtio/virtio-pci.c

@@ -1688,7 +1688,7 @@ static void virtio_pci_device_plugged(DeviceState *d, Error **errp)
         pci_set_word(config + PCI_VENDOR_ID,
                      PCI_VENDOR_ID_REDHAT_QUMRANET);
         pci_set_word(config + PCI_DEVICE_ID,
-                     0x1040 + virtio_bus_get_vdev_id(bus));
+                     PCI_DEVICE_ID_VIRTIO_10_BASE + virtio_bus_get_vdev_id(bus));
         pci_config_set_revision(config, 1);
     }
     config[PCI_INTERRUPT_PIN] = 1;

include/hw/pci/pci.h

@@ -76,6 +76,7 @@ extern bool pci_available;
 #define PCI_SUBVENDOR_ID_REDHAT_QUMRANET 0x1af4
 #define PCI_SUBDEVICE_ID_QEMU            0x1100
 
+/* legacy virtio-pci devices */
 #define PCI_DEVICE_ID_VIRTIO_NET         0x1000
 #define PCI_DEVICE_ID_VIRTIO_BLOCK       0x1001
 #define PCI_DEVICE_ID_VIRTIO_BALLOON     0x1002
@@ -85,6 +86,15 @@ extern bool pci_available;
 #define PCI_DEVICE_ID_VIRTIO_9P          0x1009
 #define PCI_DEVICE_ID_VIRTIO_VSOCK       0x1012
 
+/*
+ * modern virtio-pci devices get their id assigned automatically,
+ * there is no need to add #defines here.  It gets calculated as
+ *
+ * PCI_DEVICE_ID = PCI_DEVICE_ID_VIRTIO_10_BASE +
+ *                 virtio_bus_get_vdev_id(bus)
+ */
+#define PCI_DEVICE_ID_VIRTIO_10_BASE     0x1040
+
 #define PCI_VENDOR_ID_REDHAT             0x1b36
 #define PCI_DEVICE_ID_REDHAT_BRIDGE      0x0001
 #define PCI_DEVICE_ID_REDHAT_SERIAL      0x0002