rust: add PL011 device model

This commit adds a re-implementation of hw/char/pl011.c in Rust.

How to build:

1. Configure a QEMU build with:
   --enable-system --target-list=aarch64-softmmu --enable-rust
2. Launching a VM with qemu-system-aarch64 should use the Rust version
   of the pl011 device

Co-authored-by: Junjie Mao <junjie.mao@intel.com>
Co-authored-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Junjie Mao <junjie.mao@intel.com>
Signed-off-by: Manos Pitsidianakis <manos.pitsidianakis@linaro.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Link: https://lore.kernel.org/r/20241024-rust-round-2-v1-2-051e7a25b978@linaro.org

rust/hw/char/pl011/src/memory_ops.rs

@@ -0,0 +1,59 @@
+// Copyright 2024, Linaro Limited
+// Author(s): Manos Pitsidianakis <manos.pitsidianakis@linaro.org>
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+use core::{mem::MaybeUninit, ptr::NonNull};
+
+use qemu_api::bindings::*;
+
+use crate::device::PL011State;
+
+pub static PL011_OPS: MemoryRegionOps = MemoryRegionOps {
+    read: Some(pl011_read),
+    write: Some(pl011_write),
+    read_with_attrs: None,
+    write_with_attrs: None,
+    endianness: device_endian::DEVICE_NATIVE_ENDIAN,
+    valid: unsafe { MaybeUninit::<MemoryRegionOps__bindgen_ty_1>::zeroed().assume_init() },
+    impl_: MemoryRegionOps__bindgen_ty_2 {
+        min_access_size: 4,
+        max_access_size: 4,
+        ..unsafe { MaybeUninit::<MemoryRegionOps__bindgen_ty_2>::zeroed().assume_init() }
+    },
+};
+
+#[no_mangle]
+unsafe extern "C" fn pl011_read(
+    opaque: *mut core::ffi::c_void,
+    addr: hwaddr,
+    size: core::ffi::c_uint,
+) -> u64 {
+    assert!(!opaque.is_null());
+    let mut state = unsafe { NonNull::new_unchecked(opaque.cast::<PL011State>()) };
+    let val = unsafe { state.as_mut().read(addr, size) };
+    match val {
+        std::ops::ControlFlow::Break(val) => val,
+        std::ops::ControlFlow::Continue(val) => {
+            // SAFETY: self.char_backend is a valid CharBackend instance after it's been
+            // initialized in realize().
+            let cb_ptr = unsafe { core::ptr::addr_of_mut!(state.as_mut().char_backend) };
+            unsafe { qemu_chr_fe_accept_input(cb_ptr) };
+
+            val
+        }
+    }
+}
+
+#[no_mangle]
+unsafe extern "C" fn pl011_write(
+    opaque: *mut core::ffi::c_void,
+    addr: hwaddr,
+    data: u64,
+    _size: core::ffi::c_uint,
+) {
+    unsafe {
+        assert!(!opaque.is_null());
+        let mut state = NonNull::new_unchecked(opaque.cast::<PL011State>());
+        state.as_mut().write(addr, data)
+    }
+}