[PATCH v3] virtio-mmio: improve virtio-mmio unique device path assignment

[schspa]

At the moment the following QEMU command line triggers an assertion
failure On xlnx-versal SOC:
  qemu-system-aarch64 \
      -machine xlnx-versal-virt -nographic -smp 2 -m 128 \
      -fsdev local,id=shareid,path=${HOME}/work,security_model=none \
      -device virtio-9p-device,fsdev=shareid,mount_tag=share \
      -fsdev local,id=shareid1,path=${HOME}/Music,security_model=none \
      -device virtio-9p-device,fsdev=shareid1,mount_tag=share1

  qemu-system-aarch64: ../migration/savevm.c:860:
  vmstate_register_with_alias_id:
  Assertion `!se->compat || se->instance_id == 0' failed.

This problem was fixed on arm virt platform in commit f58b39d2d5b
("virtio-mmio: format transport base address in BusClass.get_dev_path")

It works perfectly on arm virt platform. but there is still there on
xlnx-versal SOC.

The main difference between arm virt and xlnx-versal is they use
different way to create virtio-mmio qdev. on arm virt, it calls
sysbus_create_simple("virtio-mmio", base, pic[irq]); which will call
sysbus_mmio_map internally and assign base address to subsys device
mmio correctly. but xlnx-versal's implements won't do this.

However, xlnx-versal can't switch to sysbus_create_simple() to create
virtio-mmio device. It's because xlnx-versal's cpu use
VersalVirt.soc.fpd.apu.mr as it's memory. which is subregion of
system_memory. sysbus_create_simple will add virtio to system_memory,
which can't be accessed by cpu.

Besides, xlnx-versal can't add sysbus_mmio_map api call too, because
this will add memory region to system_memory, and it can't be added
to VersalVirt.soc.fpd.apu.mr again.

We can solve this by assign correct base address offset on dev_path.

This path was test on aarch64 virt & xlnx-versal platform.

Signed-off-by: schspa <schspa@gmail.com>
---
 hw/virtio/virtio-mmio.c | 12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

diff --git a/hw/virtio/virtio-mmio.c b/hw/virtio/virtio-mmio.c
index e1b5c3b81e..8fc2ccf347 100644
--- a/hw/virtio/virtio-mmio.c
+++ b/hw/virtio/virtio-mmio.c
@@ -731,6 +731,7 @@ static char
*virtio_mmio_bus_get_dev_path(DeviceState *dev)
     char *proxy_path;
     SysBusDevice *proxy_sbd;
     char *path;
+    MemoryRegionSection section;
 
     virtio_mmio_bus = qdev_get_parent_bus(dev);
     virtio_mmio_proxy = VIRTIO_MMIO(virtio_mmio_bus->parent);
@@ -749,17 +750,18 @@ static char
*virtio_mmio_bus_get_dev_path(DeviceState *dev)
     }
 
     /* Otherwise, we append the base address of the transport. */
-    proxy_sbd = SYS_BUS_DEVICE(virtio_mmio_proxy);
-    assert(proxy_sbd->num_mmio == 1);
-    assert(proxy_sbd->mmio[0].memory == &virtio_mmio_proxy->iomem);
+    section = memory_region_find(&virtio_mmio_proxy->iomem, 0, 0x200);
+    assert(section.mr);
 
     if (proxy_path) {
         path = g_strdup_printf("%s/virtio-mmio@" TARGET_FMT_plx,
proxy_path,
-                               proxy_sbd->mmio[0].addr);
+                               section.offset_within_address_space);
     } else {
         path = g_strdup_printf("virtio-mmio@" TARGET_FMT_plx,
-                               proxy_sbd->mmio[0].addr);
+                               section.offset_within_address_space);
     }
+    memory_region_unref(section.mr);
+
     g_free(proxy_path);
     return path;
 }
-- 
2.30.0