virtio-pci: change & document virtio pci bar layout.

This patch adds variables for the pci bars (to get rid of the magic
numbers in the code) and moves the modern virtio bar to region 4 so
regions 2+3 are kept free.  virtio-vga wants use them.
Signed-off-by: NGerd Hoffmann <kraxel@redhat.com>
Reviewed-by: NMichael S. Tsirkin <mst@redhat.com>
Signed-off-by: NMichael S. Tsirkin <mst@redhat.com>
Reviewed-by: NMichael S. Tsirkin <mst@redhat.com>

hw/virtio/virtio-pci.c

@@ -926,8 +926,6 @@ static void virtio_pci_add_mem_cap(VirtIOPCIProxy *proxy,
     PCIDevice *dev = &proxy->pci_dev;
     int offset;
 
-    cap->bar = 2;
-
     offset = pci_add_capability(dev, PCI_CAP_ID_VNDR, 0, cap->cap_len);
     assert(offset > 0);
 
@@ -1203,6 +1201,22 @@ static void virtio_pci_device_plugged(DeviceState *d, Error **errp)
     uint32_t size;
     VirtIODevice *vdev = virtio_bus_get_device(&proxy->bus);
 
+    /*
+     * virtio pci bar layout
+     *
+     *   region 0   --  virtio legacy io bar
+     *   region 1   --  msi-x bar
+     *   region 2+3 --  not used by virtio-pci
+     *   region 4+5 --  virtio modern memory (64bit) bar
+     *
+     * Regions 2+3 can be used by VirtIOPCIProxy subclasses.
+     * virtio-vga places the vga framebuffer there.
+     *
+     */
+    uint32_t legacy_io_bar  = 0;
+    uint32_t msix_bar       = 1;
+    uint32_t modern_mem_bar = 4;
+
     config = proxy->pci_dev.config;
     if (proxy->class_code) {
         pci_config_set_class(config, proxy->class_code);
@@ -1228,24 +1242,28 @@ static void virtio_pci_device_plugged(DeviceState *d, Error **errp)
         struct virtio_pci_cap common = {
             .cfg_type = VIRTIO_PCI_CAP_COMMON_CFG,
             .cap_len = sizeof common,
+            .bar = modern_mem_bar,
             .offset = cpu_to_le32(0x0),
             .length = cpu_to_le32(0x1000),
         };
         struct virtio_pci_cap isr = {
             .cfg_type = VIRTIO_PCI_CAP_ISR_CFG,
             .cap_len = sizeof isr,
+            .bar = modern_mem_bar,
             .offset = cpu_to_le32(0x1000),
             .length = cpu_to_le32(0x1000),
         };
         struct virtio_pci_cap device = {
             .cfg_type = VIRTIO_PCI_CAP_DEVICE_CFG,
             .cap_len = sizeof device,
+            .bar = modern_mem_bar,
             .offset = cpu_to_le32(0x2000),
             .length = cpu_to_le32(0x1000),
         };
         struct virtio_pci_notify_cap notify = {
             .cap.cfg_type = VIRTIO_PCI_CAP_NOTIFY_CFG,
             .cap.cap_len = sizeof notify,
+            .cap.bar = modern_mem_bar,
             .cap.offset = cpu_to_le32(0x3000),
             .cap.length = cpu_to_le32(QEMU_VIRTIO_PCI_QUEUE_MEM_MULT *
                                       VIRTIO_QUEUE_MAX),
@@ -1325,12 +1343,13 @@ static void virtio_pci_device_plugged(DeviceState *d, Error **errp)
                               QEMU_VIRTIO_PCI_QUEUE_MEM_MULT *
                               VIRTIO_QUEUE_MAX);
         memory_region_add_subregion(&proxy->modern_bar, 0x3000, &proxy->notify);
-        pci_register_bar(&proxy->pci_dev, 2, PCI_BASE_ADDRESS_SPACE_MEMORY,
+        pci_register_bar(&proxy->pci_dev, modern_mem_bar,
+                         PCI_BASE_ADDRESS_SPACE_MEMORY,
                          &proxy->modern_bar);
     }
 
     if (proxy->nvectors &&
-        msix_init_exclusive_bar(&proxy->pci_dev, proxy->nvectors, 1)) {
+        msix_init_exclusive_bar(&proxy->pci_dev, proxy->nvectors, msix_bar)) {
         error_report("unable to init msix vectors to %" PRIu32,
                      proxy->nvectors);
         proxy->nvectors = 0;
@@ -1349,8 +1368,8 @@ static void virtio_pci_device_plugged(DeviceState *d, Error **errp)
                               &virtio_pci_config_ops,
                               proxy, "virtio-pci", size);
 
-        pci_register_bar(&proxy->pci_dev, 0, PCI_BASE_ADDRESS_SPACE_IO,
-                         &proxy->bar);
+        pci_register_bar(&proxy->pci_dev, legacy_io_bar,
+                         PCI_BASE_ADDRESS_SPACE_IO, &proxy->bar);
     }
 
     if (!kvm_has_many_ioeventfds()) {