Leave IRQ and MMIO initialization to instance_post_init.  In Rust the
two callbacks are more distinct, because only instance_post_init has a
fully initialized object available.

While at it, add a wrapper for sysbus_init_mmio so that accesses to
the SysBusDevice correctly use shared references.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
 rust/hw/char/pl011/src/device.rs | 18 ++++++++++--------
 rust/qemu-api/src/sysbus.rs      | 12 ++++++++++++
 2 files changed, 22 insertions(+), 8 deletions(-)

diff --git a/rust/hw/char/pl011/src/device.rs b/rust/hw/char/pl011/src/device.rs
index 215f94a6e4a..72a4cea042c 100644
--- a/rust/hw/char/pl011/src/device.rs
+++ b/rust/hw/char/pl011/src/device.rs
@@ -145,6 +145,7 @@ impl ObjectImpl for PL011State {
     type ParentType = SysBusDevice;
 
     const INSTANCE_INIT: Option<unsafe fn(&mut Self)> = Some(Self::init);
+    const INSTANCE_POST_INIT: Option<fn(&mut Self)> = Some(Self::post_init);
 }
 
 impl DeviceImpl for PL011State {
@@ -183,14 +184,6 @@ unsafe fn init(&mut self) {
                 Self::TYPE_NAME.as_ptr(),
                 0x1000,
             );
-
-            let sbd: &mut SysBusDevice = self.upcast_mut();
-            sysbus_init_mmio(sbd, addr_of_mut!(self.iomem));
-        }
-
-        for irq in self.interrupts.iter() {
-            let sbd: &SysBusDevice = self.upcast();
-            sbd.init_irq(irq);
         }
 
         // SAFETY:
@@ -213,6 +206,15 @@ unsafe fn init(&mut self) {
         }
     }
 
+    fn post_init(&mut self) {
+        let sbd: &SysBusDevice = self.upcast();
+
+        sbd.init_mmio(&self.iomem);
+        for irq in self.interrupts.iter() {
+            sbd.init_irq(irq);
+        }
+    }
+
     pub fn read(&mut self, offset: hwaddr, _size: c_uint) -> std::ops::ControlFlow<u64, u64> {
         use RegisterOffset::*;
 
diff --git a/rust/qemu-api/src/sysbus.rs b/rust/qemu-api/src/sysbus.rs
index 8193734bde4..b96eaaf25f2 100644
--- a/rust/qemu-api/src/sysbus.rs
+++ b/rust/qemu-api/src/sysbus.rs
@@ -38,6 +38,18 @@ const fn as_mut_ptr(&self) -> *mut SysBusDevice {
         addr_of!(*self) as *mut _
     }
 
+    /// Expose a memory region to the board so that it can give it an address
+    /// in guest memory.  Note that the ordering of calls to `init_mmio` is
+    /// important, since whoever creates the sysbus device will refer to the
+    /// region with a number that corresponds to the order of calls to
+    /// `init_mmio`.
+    pub fn init_mmio(&self, iomem: &bindings::MemoryRegion) {
+        assert!(bql_locked());
+        unsafe {
+            bindings::sysbus_init_mmio(self.as_mut_ptr(), addr_of!(*iomem) as *mut _);
+        }
+    }
+
     /// Expose an interrupt source outside the device as a qdev GPIO output.
     /// Note that the ordering of calls to `init_irq` is important, since
     /// whoever creates the sysbus device will refer to the interrupts with
-- 
2.47.1