[RFC PATCH V3 0/4] rust/hw: Add the I2C and the first GPIO device

[RFC PATCH V3 0/4] rust/hw: Add the I2C and the first GPIO device

[Chen Miao]

We have implemented I2C and the first GPIO device in Rust for QEMU.
Additionally, in the respective patches, we have shared our insights and
experiences regarding the use of Rust for device modeling within QEMU.

1. The first patch implements the BusState for the I2CBus infrastructure.
2. The second patch implements the I2CBus and I2CSlave infrastructure, along
   with a discussion of the challenges encountered during the implementation.
3. The third patch provides a set of necessary helper functions for the PCF8574
   GPIO device.
4. The fourth patch implements the PCF8574 GPIO device, along with a discussion
   of the issues and considerations addressed during the implementation.

Signed-off-by: Chen Miao <chenmiao@openatom.club>
Signed-off-by: Chao Liu <chao.liu@openatom.club>

chenmiao (4):
  rust/hw/core: Add the BusState of rust version
  rust/hw/core: Add rust bindings/funcs for i2c bus
  rust/hw/core: Provide some interfaces for the GPIO device
  rust/hw/gpio: Add the the first gpio device pcf8574

 hw/gpio/Kconfig                  |   5 +
 hw/gpio/meson.build              |   2 +-
 rust/Cargo.lock                  |  18 +-
 rust/Cargo.toml                  |   1 +
 rust/hw/Kconfig                  |   1 +
 rust/hw/core/meson.build         |   2 +
 rust/hw/core/src/bus.rs          |  44 +++++
 rust/hw/core/src/i2c.rs          | 303 +++++++++++++++++++++++++++++++
 rust/hw/core/src/lib.rs          |   6 +
 rust/hw/core/src/qdev.rs         |  17 +-
 rust/hw/core/wrapper.h           |   1 +
 rust/hw/gpio/Kconfig             |   2 +
 rust/hw/gpio/meson.build         |   1 +
 rust/hw/gpio/pcf8574/Cargo.toml  |  28 +++
 rust/hw/gpio/pcf8574/meson.build |  37 ++++
 rust/hw/gpio/pcf8574/src/lib.rs  | 178 ++++++++++++++++++
 rust/hw/meson.build              |   1 +
 17 files changed, 642 insertions(+), 5 deletions(-)
 create mode 100644 rust/hw/core/src/bus.rs
 create mode 100644 rust/hw/core/src/i2c.rs
 create mode 100644 rust/hw/gpio/Kconfig
 create mode 100644 rust/hw/gpio/meson.build
 create mode 100644 rust/hw/gpio/pcf8574/Cargo.toml
 create mode 100644 rust/hw/gpio/pcf8574/meson.build
 create mode 100644 rust/hw/gpio/pcf8574/src/lib.rs

-- 
2.43.0

[RFC PATCH V3 1/4] rust/hw/core: Add the BusState of rust version

[Chen Miao]

From: chenmiao <chenmiao@openatom.club>

A Rust version implementation has been designed for BusState,
which will be used for the subsequent I2CBus implementation.

Signed-off-by: Chen Miao <chenmiao@openatom.club>
Signed-off-by: Chao Liu <chao.liu@openatom.club>
---
 rust/hw/core/meson.build |  1 +
 rust/hw/core/src/bus.rs  | 44 ++++++++++++++++++++++++++++++++++++++++
 rust/hw/core/src/lib.rs  |  3 +++
 3 files changed, 48 insertions(+)
 create mode 100644 rust/hw/core/src/bus.rs

diff --git a/rust/hw/core/meson.build b/rust/hw/core/meson.build
index 1560dd20c6..efcda50fef 100644
--- a/rust/hw/core/meson.build
+++ b/rust/hw/core/meson.build
@@ -50,6 +50,7 @@ _hwcore_rs = static_library(
     [
       'src/lib.rs',
       'src/bindings.rs',
+      'src/bus.rs',
       'src/irq.rs',
       'src/qdev.rs',
       'src/sysbus.rs',
diff --git a/rust/hw/core/src/bus.rs b/rust/hw/core/src/bus.rs
new file mode 100644
index 0000000000..d3fbf519d4
--- /dev/null
+++ b/rust/hw/core/src/bus.rs
@@ -0,0 +1,44 @@
+// Copyright 2025 HUST OpenAtom Open Source Club.
+// Author(s): Chen Miao <chenmiao@openatom.club>
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+use std::ffi::CStr;
+
+pub use bindings::BusClass;
+use common::Opaque;
+use qom::{qom_isa, IsA, Object, ObjectDeref, ObjectType};
+
+use crate::{bindings, DeviceImpl};
+
+#[repr(transparent)]
+#[derive(Debug, common::Wrapper)]
+pub struct BusState(Opaque<bindings::BusState>);
+
+unsafe impl Send for BusState {}
+unsafe impl Sync for BusState {}
+
+unsafe impl ObjectType for BusState {
+    type Class = BusClass;
+    const TYPE_NAME: &'static std::ffi::CStr =
+        unsafe { CStr::from_bytes_with_nul_unchecked(bindings::TYPE_BUS) };
+}
+
+qom_isa!(BusState: Object);
+
+pub trait BusStateImpl: DeviceImpl + IsA<BusState> {}
+
+impl BusClass {
+    pub fn class_init<T: BusStateImpl>(self: &mut BusClass) {
+        self.parent_class.class_init::<T>();
+    }
+}
+
+pub trait BusMethods: ObjectDeref
+where
+    Self::Target: IsA<BusState>,
+{
+    // TODO: Since the bus does not currently provide services to other
+    // components, we have not implemented any functions yet.
+}
+
+impl<R: ObjectDeref> BusMethods for R where R::Target: IsA<BusState> {}
diff --git a/rust/hw/core/src/lib.rs b/rust/hw/core/src/lib.rs
index b40801eb84..10cc516664 100644
--- a/rust/hw/core/src/lib.rs
+++ b/rust/hw/core/src/lib.rs
@@ -13,3 +13,6 @@
 
 mod sysbus;
 pub use sysbus::*;
+
+mod bus;
+pub use bus::*;
-- 
2.43.0

[RFC PATCH V3 2/4] rust/hw/core: Add rust bindings/funcs for i2c bus

[Chen Miao]

From: chenmiao <chenmiao@openatom.club>

We have implemented the I2CBus and I2CSlave infrastructure in Rust by referring
to the SysBus device model.

Initially, we assumed that the I2CBus was at the same hierarchical level as the
PL011 device. Therefore, we followed the implementation paradigm of the PL011
device as a reference. However, in the end, we discovered that the I2CBus is
actually at the same level as the SysBus. As a result, we adopted the binding
implementation paradigm used for SysBus devices. With this adjustment, we
successfully compiled the code locally.

During the implementation process, we found that the current two paradigms in
Rust — bindings and impl — are extremely complex and lack comprehensive
documentation. There is no clear explanation as to why Bus and Device models
need to be implemented using different approaches. Furthermore, the
implementation of Bus and Device following these paradigms still has many
limitations. At present, at least vmstate is not easily supported.

Signed-off-by: Chao Liu <chao.liu@openatom.club>
Signed-off-by: Chen Miao <chenmiao@openatom.club>
---
 rust/hw/core/meson.build |   1 +
 rust/hw/core/src/i2c.rs  | 303 +++++++++++++++++++++++++++++++++++++++
 rust/hw/core/src/lib.rs  |   3 +
 rust/hw/core/wrapper.h   |   1 +
 4 files changed, 308 insertions(+)
 create mode 100644 rust/hw/core/src/i2c.rs

diff --git a/rust/hw/core/meson.build b/rust/hw/core/meson.build
index efcda50fef..1a27c1cff7 100644
--- a/rust/hw/core/meson.build
+++ b/rust/hw/core/meson.build
@@ -52,6 +52,7 @@ _hwcore_rs = static_library(
       'src/bindings.rs',
       'src/bus.rs',
       'src/irq.rs',
+      'src/i2c.rs',
       'src/qdev.rs',
       'src/sysbus.rs',
     ],
diff --git a/rust/hw/core/src/i2c.rs b/rust/hw/core/src/i2c.rs
new file mode 100644
index 0000000000..85ec34357a
--- /dev/null
+++ b/rust/hw/core/src/i2c.rs
@@ -0,0 +1,303 @@
+// Copyright 2025 HUST OpenAtom Open Source Club.
+// Author(s): Chao Liu <chao.liu@openatom.club>
+// Author(s): Chen Miao <chenmiao@openatom.club>
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+//! Bindings to access `i2c` functionality from Rust.
+
+use std::{ffi::CStr, ptr::NonNull};
+
+pub use crate::bindings::I2CSlaveClass;
+use common::{self, Opaque};
+use migration::impl_vmstate_c_struct;
+use qom::{prelude::*, Owned};
+
+use crate::{
+    bindings,
+    bus::{BusClass, BusState},
+    qdev::{DeviceImpl, DeviceState},
+};
+
+/// A safe wrapper around [`bindings::I2CBus`].
+#[repr(transparent)]
+#[derive(Debug, common::Wrapper)]
+pub struct I2CBus(Opaque<bindings::I2CBus>);
+
+unsafe impl Send for I2CBus {}
+unsafe impl Sync for I2CBus {}
+
+unsafe impl ObjectType for I2CBus {
+    type Class = BusClass;
+    const TYPE_NAME: &'static CStr =
+        unsafe { CStr::from_bytes_with_nul_unchecked(bindings::TYPE_I2C_BUS) };
+}
+
+qom_isa!(I2CBus: BusState, Object);
+
+/// Trait for methods of [`I2CBus`] and its subclasses.
+pub trait I2CBusMethods: ObjectDeref
+where
+    Self::Target: IsA<I2CBus>,
+{
+    /// # Safety
+    ///
+    /// Initialize an I2C bus
+    fn init_bus(&self, parent: &DeviceState, name: &str) -> Owned<I2CBus> {
+        assert!(bql::is_locked());
+        unsafe {
+            let bus = bindings::i2c_init_bus(parent.as_mut_ptr(), name.as_ptr().cast());
+            let bus: &I2CBus = I2CBus::from_raw(bus);
+            Owned::from(bus)
+        }
+    }
+
+    /// # Safety
+    ///
+    /// Start a transfer on an I2C bus
+    fn start_transfer(&self, address: u8, is_recv: bool) -> i32 {
+        assert!(bql::is_locked());
+        unsafe { bindings::i2c_start_transfer(self.upcast().as_mut_ptr(), address, is_recv) }
+    }
+
+    /// # Safety
+    ///
+    /// Start a receive transfer on an I2C bus
+    fn start_recv(&self, address: u8) -> i32 {
+        assert!(bql::is_locked());
+        unsafe { bindings::i2c_start_recv(self.upcast().as_mut_ptr(), address) }
+    }
+
+    /// # Safety
+    ///
+    /// Start a send transfer on an I2C bus
+    fn start_send(&self, address: u8) -> i32 {
+        assert!(bql::is_locked());
+        unsafe { bindings::i2c_start_send(self.upcast().as_mut_ptr(), address) }
+    }
+
+    /// # Safety
+    ///
+    /// End a transfer on an I2C bus
+    fn end_transfer(&self) {
+        assert!(bql::is_locked());
+        unsafe { bindings::i2c_end_transfer(self.upcast().as_mut_ptr()) }
+    }
+
+    /// # Safety
+    ///
+    /// Send NACK on an I2C bus
+    fn nack(&self) {
+        assert!(bql::is_locked());
+        unsafe { bindings::i2c_nack(self.upcast().as_mut_ptr()) }
+    }
+
+    /// # Safety
+    ///
+    /// Send ACK on an I2C bus
+    fn ack(&self) {
+        assert!(bql::is_locked());
+        unsafe { bindings::i2c_ack(self.upcast().as_mut_ptr()) }
+    }
+
+    /// # Safety
+    ///
+    /// Send data on an I2C bus
+    fn send(&self, data: u8) -> i32 {
+        assert!(bql::is_locked());
+        unsafe { bindings::i2c_send(self.upcast().as_mut_ptr(), data) }
+    }
+
+    /// # Safety
+    ///
+    /// Receive data from an I2C bus
+    fn recv(&self) -> u8 {
+        assert!(bql::is_locked());
+        unsafe { bindings::i2c_recv(self.upcast().as_mut_ptr()) }
+    }
+
+    /// # Safety
+    ///
+    /// Check if the I2C bus is busy.
+    ///
+    /// Returns `true` if the bus is busy, `false` otherwise.
+    fn is_busy(&self) -> bool {
+        assert!(bql::is_locked());
+        unsafe { bindings::i2c_bus_busy(self.upcast().as_mut_ptr()) != 0 }
+    }
+
+    /// # Safety
+    ///
+    /// Schedule pending master on an I2C bus
+    fn schedule_pending_master(&self) {
+        assert!(bql::is_locked());
+        unsafe { bindings::i2c_schedule_pending_master(self.upcast().as_mut_ptr()) }
+    }
+
+    /// Sets the I2C bus master.
+    ///
+    /// # Safety
+    ///
+    /// This function is unsafe because:
+    /// - `bh` must be a valid pointer to a `QEMUBH`.
+    /// - The caller must ensure that `self` is in a valid state.
+    /// - The caller must guarantee no data races occur during execution.
+    ///
+    /// TODO ("`i2c_bus_master` missing until QEMUBH is wrapped")
+    unsafe fn set_master(&self, bh: *mut bindings::QEMUBH) {
+        assert!(bql::is_locked());
+        unsafe { bindings::i2c_bus_master(self.upcast().as_mut_ptr(), bh) }
+    }
+}
+
+impl<R: ObjectDeref> I2CBusMethods for R where R::Target: IsA<I2CBus> {}
+
+/// A safe wrapper around [`bindings::I2CSlave`].
+#[repr(transparent)]
+#[derive(Debug, common::Wrapper)]
+pub struct I2CSlave(Opaque<bindings::I2CSlave>);
+
+unsafe impl Send for I2CSlave {}
+unsafe impl Sync for I2CSlave {}
+
+unsafe impl ObjectType for I2CSlave {
+    type Class = I2CSlaveClass;
+    const TYPE_NAME: &'static CStr =
+        unsafe { CStr::from_bytes_with_nul_unchecked(bindings::TYPE_I2C_SLAVE) };
+}
+
+qom_isa!(I2CSlave: DeviceState, Object);
+
+impl_vmstate_c_struct!(I2CSlave, bindings::vmstate_i2c_slave);
+
+#[derive(common::TryInto)]
+#[repr(u64)]
+#[allow(non_camel_case_types)]
+pub enum I2CResult {
+    ACK = 0,
+    NACK = 1,
+}
+
+// TODO: add virtual methods
+pub trait I2CSlaveImpl: DeviceImpl + IsA<I2CSlave> {
+    /// Master to slave. Returns non-zero for a NAK, 0 for success.
+    const SEND: Option<fn(&Self, data: u8) -> I2CResult> = None;
+
+    /// Slave to master. This cannot fail, the device should always return something here.
+    const RECV: Option<fn(&Self) -> u8> = None;
+
+    /// Notify the slave of a bus state change. For start event,
+    /// returns non-zero to NAK an operation. For other events the
+    /// return code is not used and should be zero.
+    const EVENT: Option<fn(&Self, event: I2CEvent) -> I2CEvent> = None;
+
+    /// Check if this device matches the address provided. Returns bool of
+    /// true if it matches (or broadcast), and updates the device list, false
+    /// otherwise.
+    ///
+    /// If broadcast is true, match should add the device and return true.
+    #[allow(clippy::type_complexity)]
+    const MATCH_AND_ADD: Option<
+        fn(&Self, address: u8, broadcast: bool, current_devs: *mut bindings::I2CNodeList) -> bool,
+    > = None;
+}
+
+/// # Safety
+///
+/// We expect the FFI user of this function to pass a valid pointer that
+/// can be downcasted to type `T`. We also expect the device is
+/// readable/writeable from one thread at any time.
+unsafe extern "C" fn rust_i2c_slave_send_fn<T: I2CSlaveImpl>(
+    obj: *mut bindings::I2CSlave,
+    data: u8,
+) -> std::os::raw::c_int {
+    let state = NonNull::new(obj).unwrap().cast::<T>();
+    T::SEND.unwrap()(unsafe { state.as_ref() }, data).into_bits() as std::os::raw::c_int
+}
+
+/// # Safety
+///
+/// We expect the FFI user of this function to pass a valid pointer that
+/// can be downcasted to type `T`. We also expect the device is
+/// readable/writeable from one thread at any time.
+unsafe extern "C" fn rust_i2c_slave_recv_fn<T: I2CSlaveImpl>(obj: *mut bindings::I2CSlave) -> u8 {
+    let state = NonNull::new(obj).unwrap().cast::<T>();
+    T::RECV.unwrap()(unsafe { state.as_ref() })
+}
+
+/// # Safety
+///
+/// We expect the FFI user of this function to pass a valid pointer that
+/// can be downcasted to type `T`. We also expect the device is
+/// readable/writeable from one thread at any time.
+unsafe extern "C" fn rust_i2c_slave_event_fn<T: I2CSlaveImpl>(
+    obj: *mut bindings::I2CSlave,
+    event: bindings::i2c_event,
+) -> std::os::raw::c_int {
+    let state = NonNull::new(obj).unwrap().cast::<T>();
+    T::EVENT.unwrap()(unsafe { state.as_ref() }, I2CEvent::from_bits(event)).into_bits()
+        as std::os::raw::c_int
+}
+
+/// # Safety
+///
+/// We expect the FFI user of this function to pass a valid pointer that
+/// can be downcasted to type `T`. We also expect the device is
+/// readable/writeable from one thread at any time.
+unsafe extern "C" fn rust_i2c_slave_match_and_add_fn<T: I2CSlaveImpl>(
+    obj: *mut bindings::I2CSlave,
+    address: u8,
+    broadcast: bool,
+    current_devs: *mut bindings::I2CNodeList,
+) -> bool {
+    let state = NonNull::new(obj).unwrap().cast::<T>();
+    T::MATCH_AND_ADD.unwrap()(unsafe { state.as_ref() }, address, broadcast, current_devs)
+}
+
+impl I2CSlaveClass {
+    /// Fill in the virtual methods of `I2CSlaveClass` based on the
+    /// definitions in the `I2CSlaveImpl` trait.
+    pub fn class_init<T: I2CSlaveImpl>(&mut self) {
+        if <T as I2CSlaveImpl>::SEND.is_some() {
+            self.send = Some(rust_i2c_slave_send_fn::<T>);
+        }
+        if <T as I2CSlaveImpl>::RECV.is_some() {
+            self.recv = Some(rust_i2c_slave_recv_fn::<T>);
+        }
+        if <T as I2CSlaveImpl>::EVENT.is_some() {
+            self.event = Some(rust_i2c_slave_event_fn::<T>);
+        }
+        if <T as I2CSlaveImpl>::MATCH_AND_ADD.is_some() {
+            self.match_and_add = Some(rust_i2c_slave_match_and_add_fn::<T>);
+        }
+        self.parent_class.class_init::<T>();
+    }
+}
+
+/// Trait for methods of [`I2CSlave`] and its subclasses.
+pub trait I2CSlaveMethods: ObjectDeref
+where
+    Self::Target: IsA<I2CSlave>,
+{
+    /// Get the I2C bus address of a slave device
+    fn get_address(&self) -> u8 {
+        assert!(bql::is_locked());
+        // SAFETY: the BQL ensures that no one else writes to the I2CSlave structure,
+        // and the I2CSlave must be initialized to get an IsA<I2CSlave>.
+        let slave = unsafe { *self.upcast().as_ptr() };
+        slave.address
+    }
+}
+
+impl<R: ObjectDeref> I2CSlaveMethods for R where R::Target: IsA<I2CSlave> {}
+
+/// Enum representing I2C events
+#[derive(common::TryInto)]
+#[repr(u32)]
+#[allow(non_camel_case_types)]
+pub enum I2CEvent {
+    START_RECV = bindings::I2C_START_RECV,
+    START_SEND = bindings::I2C_START_SEND,
+    START_SEND_ASYNC = bindings::I2C_START_SEND_ASYNC,
+    FINISH = bindings::I2C_FINISH,
+    NACK = bindings::I2C_NACK,
+}
diff --git a/rust/hw/core/src/lib.rs b/rust/hw/core/src/lib.rs
index 10cc516664..3f3aecb258 100644
--- a/rust/hw/core/src/lib.rs
+++ b/rust/hw/core/src/lib.rs
@@ -16,3 +16,6 @@
 
 mod bus;
 pub use bus::*;
+
+mod i2c;
+pub use i2c::*;
diff --git a/rust/hw/core/wrapper.h b/rust/hw/core/wrapper.h
index 3bdbd1249e..399be594da 100644
--- a/rust/hw/core/wrapper.h
+++ b/rust/hw/core/wrapper.h
@@ -30,3 +30,4 @@ typedef enum memory_order {
 #include "hw/qdev-properties.h"
 #include "hw/qdev-properties-system.h"
 #include "hw/irq.h"
+#include "hw/i2c/i2c.h"
-- 
2.43.0

[RFC PATCH V3 3/4] rust/hw/core: Provide some interfaces for the GPIO device

[Chen Miao]

From: chenmiao <chenmiao@openatom.club>

In qdev.rs, we implemented the init_gpio_out_named function, which corresponds
to the C function qdev_init_gpio_out_named. We also refactored the
init_gpio_out function to reuse the init_gpio_out_named interface.

Signed-off-by: Chen Miao <chenmiao@openatom.club>
---
 rust/hw/core/src/qdev.rs | 17 ++++++++++++++---
 1 file changed, 14 insertions(+), 3 deletions(-)

diff --git a/rust/hw/core/src/qdev.rs b/rust/hw/core/src/qdev.rs
index c3097a284d..28da94dd0a 100644
--- a/rust/hw/core/src/qdev.rs
+++ b/rust/hw/core/src/qdev.rs
@@ -17,7 +17,7 @@
 
 pub use crate::bindings::{ClockEvent, DeviceClass, Property, ResetType};
 use crate::{
-    bindings::{self, qdev_init_gpio_in, qdev_init_gpio_out, ResettableClass},
+    bindings::{self, qdev_init_gpio_in, qdev_init_gpio_out_named, ResettableClass},
     irq::InterruptSource,
 };
 
@@ -399,11 +399,22 @@ fn do_init_gpio_in(
     }
 
     fn init_gpio_out(&self, pins: &[InterruptSource]) {
+        self.init_gpio_out_named(pins, "unnamed-gpio-out", pins.len());
+    }
+
+    fn init_gpio_out_named(&self, pins: &[InterruptSource], name: &str, n: usize) {
+        let c_name = if name.is_empty() {
+            CString::new("unnamed-gpio-out").unwrap()
+        } else {
+            CString::new(name).unwrap()
+        };
+
         unsafe {
-            qdev_init_gpio_out(
+            qdev_init_gpio_out_named(
                 self.upcast().as_mut_ptr(),
                 InterruptSource::slice_as_ptr(pins),
-                pins.len() as c_int,
+                c_name.as_ptr(),
+                n as c_int,
             );
         }
     }
-- 
2.43.0

[RFC PATCH V3 4/4] rust/hw/gpio: Add the the first gpio device pcf8574

[Chen Miao]

From: chenmiao <chenmiao@openatom.club>

After implementing the I2CBus and I2CSlave, we proceeded to implement a basic
GPIO device — the PCF8574 — which depends on I2CSlave.

This patch must depend on the below link to compile normally:

https://lists.nongnu.org/archive/html/qemu-devel/2025-10/msg07356.html

At present, I have summarized the general workflow for device modeling in Rust
as follows:

1. Modify the configuration under hw/deviceto distinguish between C and Rust
   versions.
2. Create a device crate under rust/hw.
3. Add (or copy) the necessary wrappers, build.rs, and bindings.
4. Begin the device modeling process.
5. Construct the corresponding structures in Rust that mirror those in C,
   especially for “members that may change”.
6. Referencing the C implementation, define initialization functions and
   establish parent-class relationships for the Rust structure.
7. Set up ObjectImpl, DeviceImpl, and ResettablePhasesImpl.
8. Configure vmstate.
9. Implement other functional methods.

Signed-off-by: Chen Miao <chenmiao@openatom.club>
---
 hw/gpio/Kconfig                  |   5 +
 hw/gpio/meson.build              |   2 +-
 rust/Cargo.lock                  |  18 +++-
 rust/Cargo.toml                  |   1 +
 rust/hw/Kconfig                  |   1 +
 rust/hw/gpio/Kconfig             |   2 +
 rust/hw/gpio/meson.build         |   1 +
 rust/hw/gpio/pcf8574/Cargo.toml  |  28 +++++
 rust/hw/gpio/pcf8574/meson.build |  37 +++++++
 rust/hw/gpio/pcf8574/src/lib.rs  | 178 +++++++++++++++++++++++++++++++
 rust/hw/meson.build              |   1 +
 11 files changed, 272 insertions(+), 2 deletions(-)
 create mode 100644 rust/hw/gpio/Kconfig
 create mode 100644 rust/hw/gpio/meson.build
 create mode 100644 rust/hw/gpio/pcf8574/Cargo.toml
 create mode 100644 rust/hw/gpio/pcf8574/meson.build
 create mode 100644 rust/hw/gpio/pcf8574/src/lib.rs

diff --git a/hw/gpio/Kconfig b/hw/gpio/Kconfig
index a209294c20..1be534aaf6 100644
--- a/hw/gpio/Kconfig
+++ b/hw/gpio/Kconfig
@@ -27,6 +27,11 @@ config PCA9554
 config PCF8574
     bool
     depends on I2C
+    select PCF8574_C if !HAVE_RUST
+    select X_PCF8574_RUST if HAVE_RUST
+
+config PCF8574_C
+    bool
 
 config ZAURUS_SCOOP
     bool
diff --git a/hw/gpio/meson.build b/hw/gpio/meson.build
index 74840619c0..9e4b1a8fd7 100644
--- a/hw/gpio/meson.build
+++ b/hw/gpio/meson.build
@@ -17,4 +17,4 @@ system_ss.add(when: 'CONFIG_RASPI', if_true: files(
 system_ss.add(when: 'CONFIG_STM32L4X5_SOC', if_true: files('stm32l4x5_gpio.c'))
 system_ss.add(when: 'CONFIG_ASPEED_SOC', if_true: files('aspeed_gpio.c'))
 system_ss.add(when: 'CONFIG_SIFIVE_GPIO', if_true: files('sifive_gpio.c'))
-system_ss.add(when: 'CONFIG_PCF8574', if_true: files('pcf8574.c'))
+system_ss.add(when: 'CONFIG_PCF8574_C', if_true: files('pcf8574.c'))
diff --git a/rust/Cargo.lock b/rust/Cargo.lock
index 0c1df625df..2db2f70e8a 100644
--- a/rust/Cargo.lock
+++ b/rust/Cargo.lock
@@ -1,6 +1,6 @@
 # This file is automatically @generated by Cargo.
 # It is not intended for manual editing.
-version = 3
+version = 4
 
 [[package]]
 name = "anyhow"
@@ -204,6 +204,22 @@ dependencies = [
  "util",
 ]
 
+[[package]]
+name = "pcf8574"
+version = "0.1.0"
+dependencies = [
+ "bits",
+ "bql",
+ "common",
+ "glib-sys",
+ "hwcore",
+ "migration",
+ "qom",
+ "system",
+ "trace",
+ "util",
+]
+
 [[package]]
 name = "pkg-config"
 version = "0.3.32"
diff --git a/rust/Cargo.toml b/rust/Cargo.toml
index 783e626802..6a17eefe49 100644
--- a/rust/Cargo.toml
+++ b/rust/Cargo.toml
@@ -10,6 +10,7 @@ members = [
     "system",
     "hw/core",
     "hw/char/pl011",
+    "hw/gpio/pcf8574",
     "hw/timer/hpet",
     "trace",
     "util",
diff --git a/rust/hw/Kconfig b/rust/hw/Kconfig
index 36f92ec028..ba1297ca2d 100644
--- a/rust/hw/Kconfig
+++ b/rust/hw/Kconfig
@@ -1,3 +1,4 @@
 # devices Kconfig
 source char/Kconfig
+source gpio/Kconfig
 source timer/Kconfig
diff --git a/rust/hw/gpio/Kconfig b/rust/hw/gpio/Kconfig
new file mode 100644
index 0000000000..c47aa76f14
--- /dev/null
+++ b/rust/hw/gpio/Kconfig
@@ -0,0 +1,2 @@
+config X_PCF8574_RUST
+    bool
diff --git a/rust/hw/gpio/meson.build b/rust/hw/gpio/meson.build
new file mode 100644
index 0000000000..908991ad13
--- /dev/null
+++ b/rust/hw/gpio/meson.build
@@ -0,0 +1 @@
+subdir('pcf8574')
diff --git a/rust/hw/gpio/pcf8574/Cargo.toml b/rust/hw/gpio/pcf8574/Cargo.toml
new file mode 100644
index 0000000000..a3bd82f93d
--- /dev/null
+++ b/rust/hw/gpio/pcf8574/Cargo.toml
@@ -0,0 +1,28 @@
+[package]
+name = "pcf8574"
+version = "0.1.0"
+authors = ["Chen Miao <chenmiao@openatom.club>"]
+description = "pcf8574 device model for QEMU"
+resolver = "2"
+publish = false
+
+edition.workspace = true
+homepage.workspace = true
+license.workspace = true
+repository.workspace = true
+rust-version.workspace = true
+
+[dependencies]
+glib-sys.workspace = true
+bits = { path = "../../../bits" }
+common = { path = "../../../common" }
+util = { path = "../../../util" }
+bql = { path = "../../../bql" }
+migration = { path = "../../../migration" }
+qom = { path = "../../../qom" }
+system = { path = "../../../system" }
+hwcore = { path = "../../../hw/core" }
+trace = { path = "../../../trace" }
+
+[lints]
+workspace = true
diff --git a/rust/hw/gpio/pcf8574/meson.build b/rust/hw/gpio/pcf8574/meson.build
new file mode 100644
index 0000000000..f0b7f9e687
--- /dev/null
+++ b/rust/hw/gpio/pcf8574/meson.build
@@ -0,0 +1,37 @@
+# TODO: Remove this comment when the clang/libclang mismatch issue is solved.
+#
+# Rust bindings generation with `bindgen` might fail in some cases where the
+# detected `libclang` does not match the expected `clang` version/target. In
+# this case you must pass the path to `clang` and `libclang` to your build
+# command invocation using the environment variables CLANG_PATH and
+# LIBCLANG_PATH
+_libpcf8574_rs = static_library(
+  'pcf8574',
+  structured_sources(
+    [
+      'src/lib.rs',
+    ],
+  ),
+  override_options: ['rust_std=2021', 'build.rust_std=2021'],
+  rust_abi: 'rust',
+  dependencies: [
+    bilge_rs,
+    bilge_impl_rs,
+    bits_rs,
+    common_rs,
+    glib_sys_rs,
+    util_rs,
+    migration_rs,
+    bql_rs,
+    qom_rs,
+    chardev_rs,
+    system_rs,
+    hwcore_rs,
+    trace_rs
+  ],
+)
+
+rust_devices_ss.add(when: 'CONFIG_X_PCF8574_RUST', if_true: [declare_dependency(
+  link_whole: [_libpcf8574_rs],
+  variables: {'crate': 'pcf8574'},
+)])
diff --git a/rust/hw/gpio/pcf8574/src/lib.rs b/rust/hw/gpio/pcf8574/src/lib.rs
new file mode 100644
index 0000000000..4bec081876
--- /dev/null
+++ b/rust/hw/gpio/pcf8574/src/lib.rs
@@ -0,0 +1,178 @@
+// Copyright 2025 HUST OpenAtom Open Source Club.
+// Author(s): Chen Miao <chenmiao@openatom.club>
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+use std::slice::from_ref;
+
+use bql::BqlRefCell;
+use common::bitops::IntegerExt;
+use hwcore::{
+    DeviceClass, DeviceImpl, DeviceMethods, DeviceState, I2CResult, I2CSlave, I2CSlaveImpl,
+    InterruptSource, ResetType, ResettablePhasesImpl,
+};
+use migration::{
+    self, impl_vmstate_struct, vmstate_fields, vmstate_of, VMStateDescription,
+    VMStateDescriptionBuilder,
+};
+use qom::{qom_isa, IsA, Object, ObjectImpl, ObjectType, ParentField};
+
+pub const TYPE_PCF8574: &::std::ffi::CStr = c"pcf8574";
+const PORTS_COUNT: usize = 8;
+
+#[repr(C)]
+#[derive(Clone, Copy, Debug, Default)]
+pub struct PCF8574Inner {
+    pub lastrq: u8,
+    pub input: u8,
+    pub output: u8,
+}
+
+impl PCF8574Inner {
+    pub fn line_state(&self) -> u8 {
+        self.input & self.output
+    }
+
+    pub fn set_output(&mut self, data: u8) -> (u8, u8) {
+        let prev = self.line_state();
+        self.output = data;
+        let actual = self.line_state();
+        (prev, actual)
+    }
+
+    pub fn set_input(&mut self, start: u32, value: u8) -> bool {
+        self.input = self.input.deposit(start, 1, value);
+        self.has_state_changed()
+    }
+
+    pub fn receive(&mut self) -> (bool, u8) {
+        let state_changed = self.has_state_changed();
+        if state_changed {
+            self.lastrq = self.line_state();
+        }
+        (state_changed, self.lastrq)
+    }
+
+    pub fn has_state_changed(&self) -> bool {
+        self.line_state() != self.lastrq
+    }
+}
+
+#[repr(C)]
+#[derive(qom::Object, hwcore::Device)]
+pub struct PCF8574State {
+    pub parent_obj: ParentField<I2CSlave>,
+    pub inner: BqlRefCell<PCF8574Inner>,
+    pub handler: [InterruptSource; PORTS_COUNT],
+    pub intrq: InterruptSource,
+}
+
+// static_assert!(size_of::<PCF8574State>() <= size_of::<crate::bindings::PCF8574State>());
+
+qom_isa!(PCF8574State: I2CSlave, DeviceState, Object);
+
+#[allow(dead_code)]
+trait PCF8574Impl: I2CSlaveImpl + IsA<PCF8574State> {}
+
+unsafe impl ObjectType for PCF8574State {
+    type Class = DeviceClass;
+    const TYPE_NAME: &'static std::ffi::CStr = crate::TYPE_PCF8574;
+}
+
+impl PCF8574Impl for PCF8574State {}
+
+impl ObjectImpl for PCF8574State {
+    type ParentType = I2CSlave;
+    const CLASS_INIT: fn(&mut Self::Class) = Self::Class::class_init::<Self>;
+}
+
+impl DeviceImpl for PCF8574State {
+    const VMSTATE: Option<migration::VMStateDescription<Self>> = Some(VMSTATE_PCF8574);
+    const REALIZE: Option<fn(&Self) -> util::Result<()>> = Some(Self::realize);
+}
+
+impl ResettablePhasesImpl for PCF8574State {
+    const HOLD: Option<fn(&Self, ResetType)> = Some(Self::reset_hold);
+}
+
+impl I2CSlaveImpl for PCF8574State {
+    const SEND: Option<fn(&Self, data: u8) -> I2CResult> = Some(Self::send);
+    const RECV: Option<fn(&Self) -> u8> = Some(Self::recv);
+}
+
+impl PCF8574State {
+    fn send(&self, data: u8) -> I2CResult {
+        let (prev, actual) = self.inner.borrow_mut().set_output(data);
+
+        let mut diff = actual ^ prev;
+        while diff != 0 {
+            let line = diff.trailing_zeros() as u8;
+            if let Some(handler) = self.handler.get(line as usize) {
+                handler.set((actual >> line) & 1 == 1);
+            }
+            diff &= !(1 << line);
+        }
+
+        self.intrq.set(actual == self.inner.borrow().lastrq);
+
+        I2CResult::ACK
+    }
+
+    fn recv(&self) -> u8 {
+        let (has_changed, actual) = self.inner.borrow_mut().receive();
+        if has_changed {
+            self.intrq.raise();
+        }
+
+        actual
+    }
+
+    fn realize(&self) -> util::Result<()> {
+        self.init_gpio_in(self.handler_size(), PCF8574State::gpio_set);
+        self.init_gpio_out(from_ref(&self.handler[0]));
+        self.init_gpio_out_named(from_ref(&self.intrq), "nINT", 1);
+        Ok(())
+    }
+
+    fn gpio_set(&self, line: u32, level: u32) {
+        assert!(line < self.handler_size());
+
+        if self
+            .inner
+            .borrow_mut()
+            .set_input(line, u8::from(level != 0))
+        {
+            self.intrq.raise();
+        }
+    }
+
+    fn handler_size(&self) -> u32 {
+        self.handler.len() as u32
+    }
+
+    fn reset_hold(&self, _type: ResetType) {}
+}
+
+impl_vmstate_struct!(
+    PCF8574Inner,
+    VMStateDescriptionBuilder::<PCF8574Inner>::new()
+        .name(c"pcf8574/inner")
+        .version_id(0)
+        .minimum_version_id(0)
+        .fields(vmstate_fields! {
+            vmstate_of!(PCF8574Inner, lastrq),
+            vmstate_of!(PCF8574Inner, input),
+            vmstate_of!(PCF8574Inner, output),
+        })
+        .build()
+);
+
+pub const VMSTATE_PCF8574: VMStateDescription<PCF8574State> =
+    VMStateDescriptionBuilder::<PCF8574State>::new()
+        .name(c"pcf8574")
+        .version_id(0)
+        .minimum_version_id(0)
+        .fields(vmstate_fields! {
+            vmstate_of!(PCF8574State, parent_obj),
+            vmstate_of!(PCF8574State, inner),
+        })
+        .build();
diff --git a/rust/hw/meson.build b/rust/hw/meson.build
index 9749d4adfc..d6b273170e 100644
--- a/rust/hw/meson.build
+++ b/rust/hw/meson.build
@@ -1,2 +1,3 @@
 subdir('char')
+subdir('gpio')
 subdir('timer')
-- 
2.43.0

[RESEND RFC PATCH V3 0/4] rust/hw: Add the I2C and the first GPIO device

[ChenMiao]

From: Chen Miao <chenmiao@openatom.club>

We have implemented I2C and the first GPIO device in Rust for QEMU.
Additionally, in the respective patches, we have shared our insights and
experiences regarding the use of Rust for device modeling within QEMU.

1. The first patch implements the BusState for the I2CBus infrastructure.
2. The second patch implements the I2CBus and I2CSlave infrastructure, along
   with a discussion of the challenges encountered during the implementation.
3. The third patch provides a set of necessary helper functions for the PCF8574
   GPIO device.
4. The fourth patch implements the PCF8574 GPIO device, along with a discussion
   of the issues and considerations addressed during the implementation.

Signed-off-by: Chen Miao <chenmiao@openatom.club>
Signed-off-by: Chao Liu <chao.liu@openatom.club>

chenmiao (4):
  rust/hw/core: Add the BusState of rust version
  rust/hw/core: Add rust bindings/funcs for i2c bus
  rust/hw/core: Provide some interfaces for the GPIO device
  rust/hw/gpio: Add the the first gpio device pcf8574

 hw/gpio/Kconfig                  |   5 +
 hw/gpio/meson.build              |   2 +-
 rust/Cargo.lock                  |  18 +-
 rust/Cargo.toml                  |   1 +
 rust/hw/Kconfig                  |   1 +
 rust/hw/core/meson.build         |   2 +
 rust/hw/core/src/bus.rs          |  44 +++++
 rust/hw/core/src/i2c.rs          | 303 +++++++++++++++++++++++++++++++
 rust/hw/core/src/lib.rs          |   6 +
 rust/hw/core/src/qdev.rs         |  17 +-
 rust/hw/core/wrapper.h           |   1 +
 rust/hw/gpio/Kconfig             |   2 +
 rust/hw/gpio/meson.build         |   1 +
 rust/hw/gpio/pcf8574/Cargo.toml  |  28 +++
 rust/hw/gpio/pcf8574/meson.build |  37 ++++
 rust/hw/gpio/pcf8574/src/lib.rs  | 178 ++++++++++++++++++
 rust/hw/meson.build              |   1 +
 17 files changed, 642 insertions(+), 5 deletions(-)
 create mode 100644 rust/hw/core/src/bus.rs
 create mode 100644 rust/hw/core/src/i2c.rs
 create mode 100644 rust/hw/gpio/Kconfig
 create mode 100644 rust/hw/gpio/meson.build
 create mode 100644 rust/hw/gpio/pcf8574/Cargo.toml
 create mode 100644 rust/hw/gpio/pcf8574/meson.build
 create mode 100644 rust/hw/gpio/pcf8574/src/lib.rs

-- 
2.43.0

[RESEND RFC PATCH V3 1/4] rust/hw/core: Add the BusState of rust version

[ChenMiao]

From: chenmiao <chenmiao@openatom.club>

A Rust version implementation has been designed for BusState,
which will be used for the subsequent I2CBus implementation.

Signed-off-by: Chen Miao <chenmiao@openatom.club>
Signed-off-by: Chao Liu <chao.liu@openatom.club>
---
 rust/hw/core/meson.build |  1 +
 rust/hw/core/src/bus.rs  | 44 ++++++++++++++++++++++++++++++++++++++++
 rust/hw/core/src/lib.rs  |  3 +++
 3 files changed, 48 insertions(+)
 create mode 100644 rust/hw/core/src/bus.rs

diff --git a/rust/hw/core/meson.build b/rust/hw/core/meson.build
index 1560dd20c6..efcda50fef 100644
--- a/rust/hw/core/meson.build
+++ b/rust/hw/core/meson.build
@@ -50,6 +50,7 @@ _hwcore_rs = static_library(
     [
       'src/lib.rs',
       'src/bindings.rs',
+      'src/bus.rs',
       'src/irq.rs',
       'src/qdev.rs',
       'src/sysbus.rs',
diff --git a/rust/hw/core/src/bus.rs b/rust/hw/core/src/bus.rs
new file mode 100644
index 0000000000..d3fbf519d4
--- /dev/null
+++ b/rust/hw/core/src/bus.rs
@@ -0,0 +1,44 @@
+// Copyright 2025 HUST OpenAtom Open Source Club.
+// Author(s): Chen Miao <chenmiao@openatom.club>
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+use std::ffi::CStr;
+
+pub use bindings::BusClass;
+use common::Opaque;
+use qom::{qom_isa, IsA, Object, ObjectDeref, ObjectType};
+
+use crate::{bindings, DeviceImpl};
+
+#[repr(transparent)]
+#[derive(Debug, common::Wrapper)]
+pub struct BusState(Opaque<bindings::BusState>);
+
+unsafe impl Send for BusState {}
+unsafe impl Sync for BusState {}
+
+unsafe impl ObjectType for BusState {
+    type Class = BusClass;
+    const TYPE_NAME: &'static std::ffi::CStr =
+        unsafe { CStr::from_bytes_with_nul_unchecked(bindings::TYPE_BUS) };
+}
+
+qom_isa!(BusState: Object);
+
+pub trait BusStateImpl: DeviceImpl + IsA<BusState> {}
+
+impl BusClass {
+    pub fn class_init<T: BusStateImpl>(self: &mut BusClass) {
+        self.parent_class.class_init::<T>();
+    }
+}
+
+pub trait BusMethods: ObjectDeref
+where
+    Self::Target: IsA<BusState>,
+{
+    // TODO: Since the bus does not currently provide services to other
+    // components, we have not implemented any functions yet.
+}
+
+impl<R: ObjectDeref> BusMethods for R where R::Target: IsA<BusState> {}
diff --git a/rust/hw/core/src/lib.rs b/rust/hw/core/src/lib.rs
index b40801eb84..10cc516664 100644
--- a/rust/hw/core/src/lib.rs
+++ b/rust/hw/core/src/lib.rs
@@ -13,3 +13,6 @@
 
 mod sysbus;
 pub use sysbus::*;
+
+mod bus;
+pub use bus::*;
-- 
2.43.0

[RESEND RFC PATCH V3 2/4] rust/hw/core: Add rust bindings/funcs for i2c bus

[ChenMiao]

From: chenmiao <chenmiao@openatom.club>

We have implemented the I2CBus and I2CSlave infrastructure in Rust by referring
to the SysBus device model.

Initially, we assumed that the I2CBus was at the same hierarchical level as the
PL011 device. Therefore, we followed the implementation paradigm of the PL011
device as a reference. However, in the end, we discovered that the I2CBus is
actually at the same level as the SysBus. As a result, we adopted the binding
implementation paradigm used for SysBus devices. With this adjustment, we
successfully compiled the code locally.

During the implementation process, we found that the current two paradigms in
Rust — bindings and impl — are extremely complex and lack comprehensive
documentation. There is no clear explanation as to why Bus and Device models
need to be implemented using different approaches. Furthermore, the
implementation of Bus and Device following these paradigms still has many
limitations. At present, at least vmstate is not easily supported.

Signed-off-by: Chao Liu <chao.liu@openatom.club>
Signed-off-by: Chen Miao <chenmiao@openatom.club>
---
 rust/hw/core/meson.build |   1 +
 rust/hw/core/src/i2c.rs  | 303 +++++++++++++++++++++++++++++++++++++++
 rust/hw/core/src/lib.rs  |   3 +
 rust/hw/core/wrapper.h   |   1 +
 4 files changed, 308 insertions(+)
 create mode 100644 rust/hw/core/src/i2c.rs

diff --git a/rust/hw/core/meson.build b/rust/hw/core/meson.build
index efcda50fef..1a27c1cff7 100644
--- a/rust/hw/core/meson.build
+++ b/rust/hw/core/meson.build
@@ -52,6 +52,7 @@ _hwcore_rs = static_library(
       'src/bindings.rs',
       'src/bus.rs',
       'src/irq.rs',
+      'src/i2c.rs',
       'src/qdev.rs',
       'src/sysbus.rs',
     ],
diff --git a/rust/hw/core/src/i2c.rs b/rust/hw/core/src/i2c.rs
new file mode 100644
index 0000000000..85ec34357a
--- /dev/null
+++ b/rust/hw/core/src/i2c.rs
@@ -0,0 +1,303 @@
+// Copyright 2025 HUST OpenAtom Open Source Club.
+// Author(s): Chao Liu <chao.liu@openatom.club>
+// Author(s): Chen Miao <chenmiao@openatom.club>
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+//! Bindings to access `i2c` functionality from Rust.
+
+use std::{ffi::CStr, ptr::NonNull};
+
+pub use crate::bindings::I2CSlaveClass;
+use common::{self, Opaque};
+use migration::impl_vmstate_c_struct;
+use qom::{prelude::*, Owned};
+
+use crate::{
+    bindings,
+    bus::{BusClass, BusState},
+    qdev::{DeviceImpl, DeviceState},
+};
+
+/// A safe wrapper around [`bindings::I2CBus`].
+#[repr(transparent)]
+#[derive(Debug, common::Wrapper)]
+pub struct I2CBus(Opaque<bindings::I2CBus>);
+
+unsafe impl Send for I2CBus {}
+unsafe impl Sync for I2CBus {}
+
+unsafe impl ObjectType for I2CBus {
+    type Class = BusClass;
+    const TYPE_NAME: &'static CStr =
+        unsafe { CStr::from_bytes_with_nul_unchecked(bindings::TYPE_I2C_BUS) };
+}
+
+qom_isa!(I2CBus: BusState, Object);
+
+/// Trait for methods of [`I2CBus`] and its subclasses.
+pub trait I2CBusMethods: ObjectDeref
+where
+    Self::Target: IsA<I2CBus>,
+{
+    /// # Safety
+    ///
+    /// Initialize an I2C bus
+    fn init_bus(&self, parent: &DeviceState, name: &str) -> Owned<I2CBus> {
+        assert!(bql::is_locked());
+        unsafe {
+            let bus = bindings::i2c_init_bus(parent.as_mut_ptr(), name.as_ptr().cast());
+            let bus: &I2CBus = I2CBus::from_raw(bus);
+            Owned::from(bus)
+        }
+    }
+
+    /// # Safety
+    ///
+    /// Start a transfer on an I2C bus
+    fn start_transfer(&self, address: u8, is_recv: bool) -> i32 {
+        assert!(bql::is_locked());
+        unsafe { bindings::i2c_start_transfer(self.upcast().as_mut_ptr(), address, is_recv) }
+    }
+
+    /// # Safety
+    ///
+    /// Start a receive transfer on an I2C bus
+    fn start_recv(&self, address: u8) -> i32 {
+        assert!(bql::is_locked());
+        unsafe { bindings::i2c_start_recv(self.upcast().as_mut_ptr(), address) }
+    }
+
+    /// # Safety
+    ///
+    /// Start a send transfer on an I2C bus
+    fn start_send(&self, address: u8) -> i32 {
+        assert!(bql::is_locked());
+        unsafe { bindings::i2c_start_send(self.upcast().as_mut_ptr(), address) }
+    }
+
+    /// # Safety
+    ///
+    /// End a transfer on an I2C bus
+    fn end_transfer(&self) {
+        assert!(bql::is_locked());
+        unsafe { bindings::i2c_end_transfer(self.upcast().as_mut_ptr()) }
+    }
+
+    /// # Safety
+    ///
+    /// Send NACK on an I2C bus
+    fn nack(&self) {
+        assert!(bql::is_locked());
+        unsafe { bindings::i2c_nack(self.upcast().as_mut_ptr()) }
+    }
+
+    /// # Safety
+    ///
+    /// Send ACK on an I2C bus
+    fn ack(&self) {
+        assert!(bql::is_locked());
+        unsafe { bindings::i2c_ack(self.upcast().as_mut_ptr()) }
+    }
+
+    /// # Safety
+    ///
+    /// Send data on an I2C bus
+    fn send(&self, data: u8) -> i32 {
+        assert!(bql::is_locked());
+        unsafe { bindings::i2c_send(self.upcast().as_mut_ptr(), data) }
+    }
+
+    /// # Safety
+    ///
+    /// Receive data from an I2C bus
+    fn recv(&self) -> u8 {
+        assert!(bql::is_locked());
+        unsafe { bindings::i2c_recv(self.upcast().as_mut_ptr()) }
+    }
+
+    /// # Safety
+    ///
+    /// Check if the I2C bus is busy.
+    ///
+    /// Returns `true` if the bus is busy, `false` otherwise.
+    fn is_busy(&self) -> bool {
+        assert!(bql::is_locked());
+        unsafe { bindings::i2c_bus_busy(self.upcast().as_mut_ptr()) != 0 }
+    }
+
+    /// # Safety
+    ///
+    /// Schedule pending master on an I2C bus
+    fn schedule_pending_master(&self) {
+        assert!(bql::is_locked());
+        unsafe { bindings::i2c_schedule_pending_master(self.upcast().as_mut_ptr()) }
+    }
+
+    /// Sets the I2C bus master.
+    ///
+    /// # Safety
+    ///
+    /// This function is unsafe because:
+    /// - `bh` must be a valid pointer to a `QEMUBH`.
+    /// - The caller must ensure that `self` is in a valid state.
+    /// - The caller must guarantee no data races occur during execution.
+    ///
+    /// TODO ("`i2c_bus_master` missing until QEMUBH is wrapped")
+    unsafe fn set_master(&self, bh: *mut bindings::QEMUBH) {
+        assert!(bql::is_locked());
+        unsafe { bindings::i2c_bus_master(self.upcast().as_mut_ptr(), bh) }
+    }
+}
+
+impl<R: ObjectDeref> I2CBusMethods for R where R::Target: IsA<I2CBus> {}
+
+/// A safe wrapper around [`bindings::I2CSlave`].
+#[repr(transparent)]
+#[derive(Debug, common::Wrapper)]
+pub struct I2CSlave(Opaque<bindings::I2CSlave>);
+
+unsafe impl Send for I2CSlave {}
+unsafe impl Sync for I2CSlave {}
+
+unsafe impl ObjectType for I2CSlave {
+    type Class = I2CSlaveClass;
+    const TYPE_NAME: &'static CStr =
+        unsafe { CStr::from_bytes_with_nul_unchecked(bindings::TYPE_I2C_SLAVE) };
+}
+
+qom_isa!(I2CSlave: DeviceState, Object);
+
+impl_vmstate_c_struct!(I2CSlave, bindings::vmstate_i2c_slave);
+
+#[derive(common::TryInto)]
+#[repr(u64)]
+#[allow(non_camel_case_types)]
+pub enum I2CResult {
+    ACK = 0,
+    NACK = 1,
+}
+
+// TODO: add virtual methods
+pub trait I2CSlaveImpl: DeviceImpl + IsA<I2CSlave> {
+    /// Master to slave. Returns non-zero for a NAK, 0 for success.
+    const SEND: Option<fn(&Self, data: u8) -> I2CResult> = None;
+
+    /// Slave to master. This cannot fail, the device should always return something here.
+    const RECV: Option<fn(&Self) -> u8> = None;
+
+    /// Notify the slave of a bus state change. For start event,
+    /// returns non-zero to NAK an operation. For other events the
+    /// return code is not used and should be zero.
+    const EVENT: Option<fn(&Self, event: I2CEvent) -> I2CEvent> = None;
+
+    /// Check if this device matches the address provided. Returns bool of
+    /// true if it matches (or broadcast), and updates the device list, false
+    /// otherwise.
+    ///
+    /// If broadcast is true, match should add the device and return true.
+    #[allow(clippy::type_complexity)]
+    const MATCH_AND_ADD: Option<
+        fn(&Self, address: u8, broadcast: bool, current_devs: *mut bindings::I2CNodeList) -> bool,
+    > = None;
+}
+
+/// # Safety
+///
+/// We expect the FFI user of this function to pass a valid pointer that
+/// can be downcasted to type `T`. We also expect the device is
+/// readable/writeable from one thread at any time.
+unsafe extern "C" fn rust_i2c_slave_send_fn<T: I2CSlaveImpl>(
+    obj: *mut bindings::I2CSlave,
+    data: u8,
+) -> std::os::raw::c_int {
+    let state = NonNull::new(obj).unwrap().cast::<T>();
+    T::SEND.unwrap()(unsafe { state.as_ref() }, data).into_bits() as std::os::raw::c_int
+}
+
+/// # Safety
+///
+/// We expect the FFI user of this function to pass a valid pointer that
+/// can be downcasted to type `T`. We also expect the device is
+/// readable/writeable from one thread at any time.
+unsafe extern "C" fn rust_i2c_slave_recv_fn<T: I2CSlaveImpl>(obj: *mut bindings::I2CSlave) -> u8 {
+    let state = NonNull::new(obj).unwrap().cast::<T>();
+    T::RECV.unwrap()(unsafe { state.as_ref() })
+}
+
+/// # Safety
+///
+/// We expect the FFI user of this function to pass a valid pointer that
+/// can be downcasted to type `T`. We also expect the device is
+/// readable/writeable from one thread at any time.
+unsafe extern "C" fn rust_i2c_slave_event_fn<T: I2CSlaveImpl>(
+    obj: *mut bindings::I2CSlave,
+    event: bindings::i2c_event,
+) -> std::os::raw::c_int {
+    let state = NonNull::new(obj).unwrap().cast::<T>();
+    T::EVENT.unwrap()(unsafe { state.as_ref() }, I2CEvent::from_bits(event)).into_bits()
+        as std::os::raw::c_int
+}
+
+/// # Safety
+///
+/// We expect the FFI user of this function to pass a valid pointer that
+/// can be downcasted to type `T`. We also expect the device is
+/// readable/writeable from one thread at any time.
+unsafe extern "C" fn rust_i2c_slave_match_and_add_fn<T: I2CSlaveImpl>(
+    obj: *mut bindings::I2CSlave,
+    address: u8,
+    broadcast: bool,
+    current_devs: *mut bindings::I2CNodeList,
+) -> bool {
+    let state = NonNull::new(obj).unwrap().cast::<T>();
+    T::MATCH_AND_ADD.unwrap()(unsafe { state.as_ref() }, address, broadcast, current_devs)
+}
+
+impl I2CSlaveClass {
+    /// Fill in the virtual methods of `I2CSlaveClass` based on the
+    /// definitions in the `I2CSlaveImpl` trait.
+    pub fn class_init<T: I2CSlaveImpl>(&mut self) {
+        if <T as I2CSlaveImpl>::SEND.is_some() {
+            self.send = Some(rust_i2c_slave_send_fn::<T>);
+        }
+        if <T as I2CSlaveImpl>::RECV.is_some() {
+            self.recv = Some(rust_i2c_slave_recv_fn::<T>);
+        }
+        if <T as I2CSlaveImpl>::EVENT.is_some() {
+            self.event = Some(rust_i2c_slave_event_fn::<T>);
+        }
+        if <T as I2CSlaveImpl>::MATCH_AND_ADD.is_some() {
+            self.match_and_add = Some(rust_i2c_slave_match_and_add_fn::<T>);
+        }
+        self.parent_class.class_init::<T>();
+    }
+}
+
+/// Trait for methods of [`I2CSlave`] and its subclasses.
+pub trait I2CSlaveMethods: ObjectDeref
+where
+    Self::Target: IsA<I2CSlave>,
+{
+    /// Get the I2C bus address of a slave device
+    fn get_address(&self) -> u8 {
+        assert!(bql::is_locked());
+        // SAFETY: the BQL ensures that no one else writes to the I2CSlave structure,
+        // and the I2CSlave must be initialized to get an IsA<I2CSlave>.
+        let slave = unsafe { *self.upcast().as_ptr() };
+        slave.address
+    }
+}
+
+impl<R: ObjectDeref> I2CSlaveMethods for R where R::Target: IsA<I2CSlave> {}
+
+/// Enum representing I2C events
+#[derive(common::TryInto)]
+#[repr(u32)]
+#[allow(non_camel_case_types)]
+pub enum I2CEvent {
+    START_RECV = bindings::I2C_START_RECV,
+    START_SEND = bindings::I2C_START_SEND,
+    START_SEND_ASYNC = bindings::I2C_START_SEND_ASYNC,
+    FINISH = bindings::I2C_FINISH,
+    NACK = bindings::I2C_NACK,
+}
diff --git a/rust/hw/core/src/lib.rs b/rust/hw/core/src/lib.rs
index 10cc516664..3f3aecb258 100644
--- a/rust/hw/core/src/lib.rs
+++ b/rust/hw/core/src/lib.rs
@@ -16,3 +16,6 @@
 
 mod bus;
 pub use bus::*;
+
+mod i2c;
+pub use i2c::*;
diff --git a/rust/hw/core/wrapper.h b/rust/hw/core/wrapper.h
index 3bdbd1249e..399be594da 100644
--- a/rust/hw/core/wrapper.h
+++ b/rust/hw/core/wrapper.h
@@ -30,3 +30,4 @@ typedef enum memory_order {
 #include "hw/qdev-properties.h"
 #include "hw/qdev-properties-system.h"
 #include "hw/irq.h"
+#include "hw/i2c/i2c.h"
-- 
2.43.0

[RESEND RFC PATCH V3 3/4] rust/hw/core: Provide some interfaces for the GPIO device

[ChenMiao]

From: chenmiao <chenmiao@openatom.club>

In qdev.rs, we implemented the init_gpio_out_named function, which corresponds
to the C function qdev_init_gpio_out_named. We also refactored the
init_gpio_out function to reuse the init_gpio_out_named interface.

Signed-off-by: Chen Miao <chenmiao@openatom.club>
---
 rust/hw/core/src/qdev.rs | 17 ++++++++++++++---
 1 file changed, 14 insertions(+), 3 deletions(-)

diff --git a/rust/hw/core/src/qdev.rs b/rust/hw/core/src/qdev.rs
index c3097a284d..28da94dd0a 100644
--- a/rust/hw/core/src/qdev.rs
+++ b/rust/hw/core/src/qdev.rs
@@ -17,7 +17,7 @@
 
 pub use crate::bindings::{ClockEvent, DeviceClass, Property, ResetType};
 use crate::{
-    bindings::{self, qdev_init_gpio_in, qdev_init_gpio_out, ResettableClass},
+    bindings::{self, qdev_init_gpio_in, qdev_init_gpio_out_named, ResettableClass},
     irq::InterruptSource,
 };
 
@@ -399,11 +399,22 @@ fn do_init_gpio_in(
     }
 
     fn init_gpio_out(&self, pins: &[InterruptSource]) {
+        self.init_gpio_out_named(pins, "unnamed-gpio-out", pins.len());
+    }
+
+    fn init_gpio_out_named(&self, pins: &[InterruptSource], name: &str, n: usize) {
+        let c_name = if name.is_empty() {
+            CString::new("unnamed-gpio-out").unwrap()
+        } else {
+            CString::new(name).unwrap()
+        };
+
         unsafe {
-            qdev_init_gpio_out(
+            qdev_init_gpio_out_named(
                 self.upcast().as_mut_ptr(),
                 InterruptSource::slice_as_ptr(pins),
-                pins.len() as c_int,
+                c_name.as_ptr(),
+                n as c_int,
             );
         }
     }
-- 
2.43.0

[RESEND RFC PATCH V3 4/4] rust/hw/gpio: Add the the first gpio device pcf8574

[ChenMiao]

From: chenmiao <chenmiao@openatom.club>

After implementing the I2CBus and I2CSlave, we proceeded to implement a basic
GPIO device — the PCF8574 — which depends on I2CSlave.

This patch must depend on the below link to compile normally:

https://lists.nongnu.org/archive/html/qemu-devel/2025-10/msg07356.html

At present, I have summarized the general workflow for device modeling in Rust
as follows:

1. Modify the configuration under hw/deviceto distinguish between C and Rust
   versions.
2. Create a device crate under rust/hw.
3. Add (or copy) the necessary wrappers, build.rs, and bindings.
4. Begin the device modeling process.
5. Construct the corresponding structures in Rust that mirror those in C,
   especially for “members that may change”.
6. Referencing the C implementation, define initialization functions and
   establish parent-class relationships for the Rust structure.
7. Set up ObjectImpl, DeviceImpl, and ResettablePhasesImpl.
8. Configure vmstate.
9. Implement other functional methods.

Signed-off-by: Chen Miao <chenmiao@openatom.club>
---
 hw/gpio/Kconfig                  |   5 +
 hw/gpio/meson.build              |   2 +-
 rust/Cargo.lock                  |  18 +++-
 rust/Cargo.toml                  |   1 +
 rust/hw/Kconfig                  |   1 +
 rust/hw/gpio/Kconfig             |   2 +
 rust/hw/gpio/meson.build         |   1 +
 rust/hw/gpio/pcf8574/Cargo.toml  |  28 +++++
 rust/hw/gpio/pcf8574/meson.build |  37 +++++++
 rust/hw/gpio/pcf8574/src/lib.rs  | 178 +++++++++++++++++++++++++++++++
 rust/hw/meson.build              |   1 +
 11 files changed, 272 insertions(+), 2 deletions(-)
 create mode 100644 rust/hw/gpio/Kconfig
 create mode 100644 rust/hw/gpio/meson.build
 create mode 100644 rust/hw/gpio/pcf8574/Cargo.toml
 create mode 100644 rust/hw/gpio/pcf8574/meson.build
 create mode 100644 rust/hw/gpio/pcf8574/src/lib.rs

diff --git a/hw/gpio/Kconfig b/hw/gpio/Kconfig
index a209294c20..1be534aaf6 100644
--- a/hw/gpio/Kconfig
+++ b/hw/gpio/Kconfig
@@ -27,6 +27,11 @@ config PCA9554
 config PCF8574
     bool
     depends on I2C
+    select PCF8574_C if !HAVE_RUST
+    select X_PCF8574_RUST if HAVE_RUST
+
+config PCF8574_C
+    bool
 
 config ZAURUS_SCOOP
     bool
diff --git a/hw/gpio/meson.build b/hw/gpio/meson.build
index 74840619c0..9e4b1a8fd7 100644
--- a/hw/gpio/meson.build
+++ b/hw/gpio/meson.build
@@ -17,4 +17,4 @@ system_ss.add(when: 'CONFIG_RASPI', if_true: files(
 system_ss.add(when: 'CONFIG_STM32L4X5_SOC', if_true: files('stm32l4x5_gpio.c'))
 system_ss.add(when: 'CONFIG_ASPEED_SOC', if_true: files('aspeed_gpio.c'))
 system_ss.add(when: 'CONFIG_SIFIVE_GPIO', if_true: files('sifive_gpio.c'))
-system_ss.add(when: 'CONFIG_PCF8574', if_true: files('pcf8574.c'))
+system_ss.add(when: 'CONFIG_PCF8574_C', if_true: files('pcf8574.c'))
diff --git a/rust/Cargo.lock b/rust/Cargo.lock
index 0c1df625df..2db2f70e8a 100644
--- a/rust/Cargo.lock
+++ b/rust/Cargo.lock
@@ -1,6 +1,6 @@
 # This file is automatically @generated by Cargo.
 # It is not intended for manual editing.
-version = 3
+version = 4
 
 [[package]]
 name = "anyhow"
@@ -204,6 +204,22 @@ dependencies = [
  "util",
 ]
 
+[[package]]
+name = "pcf8574"
+version = "0.1.0"
+dependencies = [
+ "bits",
+ "bql",
+ "common",
+ "glib-sys",
+ "hwcore",
+ "migration",
+ "qom",
+ "system",
+ "trace",
+ "util",
+]
+
 [[package]]
 name = "pkg-config"
 version = "0.3.32"
diff --git a/rust/Cargo.toml b/rust/Cargo.toml
index 783e626802..6a17eefe49 100644
--- a/rust/Cargo.toml
+++ b/rust/Cargo.toml
@@ -10,6 +10,7 @@ members = [
     "system",
     "hw/core",
     "hw/char/pl011",
+    "hw/gpio/pcf8574",
     "hw/timer/hpet",
     "trace",
     "util",
diff --git a/rust/hw/Kconfig b/rust/hw/Kconfig
index 36f92ec028..ba1297ca2d 100644
--- a/rust/hw/Kconfig
+++ b/rust/hw/Kconfig
@@ -1,3 +1,4 @@
 # devices Kconfig
 source char/Kconfig
+source gpio/Kconfig
 source timer/Kconfig
diff --git a/rust/hw/gpio/Kconfig b/rust/hw/gpio/Kconfig
new file mode 100644
index 0000000000..c47aa76f14
--- /dev/null
+++ b/rust/hw/gpio/Kconfig
@@ -0,0 +1,2 @@
+config X_PCF8574_RUST
+    bool
diff --git a/rust/hw/gpio/meson.build b/rust/hw/gpio/meson.build
new file mode 100644
index 0000000000..908991ad13
--- /dev/null
+++ b/rust/hw/gpio/meson.build
@@ -0,0 +1 @@
+subdir('pcf8574')
diff --git a/rust/hw/gpio/pcf8574/Cargo.toml b/rust/hw/gpio/pcf8574/Cargo.toml
new file mode 100644
index 0000000000..a3bd82f93d
--- /dev/null
+++ b/rust/hw/gpio/pcf8574/Cargo.toml
@@ -0,0 +1,28 @@
+[package]
+name = "pcf8574"
+version = "0.1.0"
+authors = ["Chen Miao <chenmiao@openatom.club>"]
+description = "pcf8574 device model for QEMU"
+resolver = "2"
+publish = false
+
+edition.workspace = true
+homepage.workspace = true
+license.workspace = true
+repository.workspace = true
+rust-version.workspace = true
+
+[dependencies]
+glib-sys.workspace = true
+bits = { path = "../../../bits" }
+common = { path = "../../../common" }
+util = { path = "../../../util" }
+bql = { path = "../../../bql" }
+migration = { path = "../../../migration" }
+qom = { path = "../../../qom" }
+system = { path = "../../../system" }
+hwcore = { path = "../../../hw/core" }
+trace = { path = "../../../trace" }
+
+[lints]
+workspace = true
diff --git a/rust/hw/gpio/pcf8574/meson.build b/rust/hw/gpio/pcf8574/meson.build
new file mode 100644
index 0000000000..f0b7f9e687
--- /dev/null
+++ b/rust/hw/gpio/pcf8574/meson.build
@@ -0,0 +1,37 @@
+# TODO: Remove this comment when the clang/libclang mismatch issue is solved.
+#
+# Rust bindings generation with `bindgen` might fail in some cases where the
+# detected `libclang` does not match the expected `clang` version/target. In
+# this case you must pass the path to `clang` and `libclang` to your build
+# command invocation using the environment variables CLANG_PATH and
+# LIBCLANG_PATH
+_libpcf8574_rs = static_library(
+  'pcf8574',
+  structured_sources(
+    [
+      'src/lib.rs',
+    ],
+  ),
+  override_options: ['rust_std=2021', 'build.rust_std=2021'],
+  rust_abi: 'rust',
+  dependencies: [
+    bilge_rs,
+    bilge_impl_rs,
+    bits_rs,
+    common_rs,
+    glib_sys_rs,
+    util_rs,
+    migration_rs,
+    bql_rs,
+    qom_rs,
+    chardev_rs,
+    system_rs,
+    hwcore_rs,
+    trace_rs
+  ],
+)
+
+rust_devices_ss.add(when: 'CONFIG_X_PCF8574_RUST', if_true: [declare_dependency(
+  link_whole: [_libpcf8574_rs],
+  variables: {'crate': 'pcf8574'},
+)])
diff --git a/rust/hw/gpio/pcf8574/src/lib.rs b/rust/hw/gpio/pcf8574/src/lib.rs
new file mode 100644
index 0000000000..4bec081876
--- /dev/null
+++ b/rust/hw/gpio/pcf8574/src/lib.rs
@@ -0,0 +1,178 @@
+// Copyright 2025 HUST OpenAtom Open Source Club.
+// Author(s): Chen Miao <chenmiao@openatom.club>
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+use std::slice::from_ref;
+
+use bql::BqlRefCell;
+use common::bitops::IntegerExt;
+use hwcore::{
+    DeviceClass, DeviceImpl, DeviceMethods, DeviceState, I2CResult, I2CSlave, I2CSlaveImpl,
+    InterruptSource, ResetType, ResettablePhasesImpl,
+};
+use migration::{
+    self, impl_vmstate_struct, vmstate_fields, vmstate_of, VMStateDescription,
+    VMStateDescriptionBuilder,
+};
+use qom::{qom_isa, IsA, Object, ObjectImpl, ObjectType, ParentField};
+
+pub const TYPE_PCF8574: &::std::ffi::CStr = c"pcf8574";
+const PORTS_COUNT: usize = 8;
+
+#[repr(C)]
+#[derive(Clone, Copy, Debug, Default)]
+pub struct PCF8574Inner {
+    pub lastrq: u8,
+    pub input: u8,
+    pub output: u8,
+}
+
+impl PCF8574Inner {
+    pub fn line_state(&self) -> u8 {
+        self.input & self.output
+    }
+
+    pub fn set_output(&mut self, data: u8) -> (u8, u8) {
+        let prev = self.line_state();
+        self.output = data;
+        let actual = self.line_state();
+        (prev, actual)
+    }
+
+    pub fn set_input(&mut self, start: u32, value: u8) -> bool {
+        self.input = self.input.deposit(start, 1, value);
+        self.has_state_changed()
+    }
+
+    pub fn receive(&mut self) -> (bool, u8) {
+        let state_changed = self.has_state_changed();
+        if state_changed {
+            self.lastrq = self.line_state();
+        }
+        (state_changed, self.lastrq)
+    }
+
+    pub fn has_state_changed(&self) -> bool {
+        self.line_state() != self.lastrq
+    }
+}
+
+#[repr(C)]
+#[derive(qom::Object, hwcore::Device)]
+pub struct PCF8574State {
+    pub parent_obj: ParentField<I2CSlave>,
+    pub inner: BqlRefCell<PCF8574Inner>,
+    pub handler: [InterruptSource; PORTS_COUNT],
+    pub intrq: InterruptSource,
+}
+
+// static_assert!(size_of::<PCF8574State>() <= size_of::<crate::bindings::PCF8574State>());
+
+qom_isa!(PCF8574State: I2CSlave, DeviceState, Object);
+
+#[allow(dead_code)]
+trait PCF8574Impl: I2CSlaveImpl + IsA<PCF8574State> {}
+
+unsafe impl ObjectType for PCF8574State {
+    type Class = DeviceClass;
+    const TYPE_NAME: &'static std::ffi::CStr = crate::TYPE_PCF8574;
+}
+
+impl PCF8574Impl for PCF8574State {}
+
+impl ObjectImpl for PCF8574State {
+    type ParentType = I2CSlave;
+    const CLASS_INIT: fn(&mut Self::Class) = Self::Class::class_init::<Self>;
+}
+
+impl DeviceImpl for PCF8574State {
+    const VMSTATE: Option<migration::VMStateDescription<Self>> = Some(VMSTATE_PCF8574);
+    const REALIZE: Option<fn(&Self) -> util::Result<()>> = Some(Self::realize);
+}
+
+impl ResettablePhasesImpl for PCF8574State {
+    const HOLD: Option<fn(&Self, ResetType)> = Some(Self::reset_hold);
+}
+
+impl I2CSlaveImpl for PCF8574State {
+    const SEND: Option<fn(&Self, data: u8) -> I2CResult> = Some(Self::send);
+    const RECV: Option<fn(&Self) -> u8> = Some(Self::recv);
+}
+
+impl PCF8574State {
+    fn send(&self, data: u8) -> I2CResult {
+        let (prev, actual) = self.inner.borrow_mut().set_output(data);
+
+        let mut diff = actual ^ prev;
+        while diff != 0 {
+            let line = diff.trailing_zeros() as u8;
+            if let Some(handler) = self.handler.get(line as usize) {
+                handler.set((actual >> line) & 1 == 1);
+            }
+            diff &= !(1 << line);
+        }
+
+        self.intrq.set(actual == self.inner.borrow().lastrq);
+
+        I2CResult::ACK
+    }
+
+    fn recv(&self) -> u8 {
+        let (has_changed, actual) = self.inner.borrow_mut().receive();
+        if has_changed {
+            self.intrq.raise();
+        }
+
+        actual
+    }
+
+    fn realize(&self) -> util::Result<()> {
+        self.init_gpio_in(self.handler_size(), PCF8574State::gpio_set);
+        self.init_gpio_out(from_ref(&self.handler[0]));
+        self.init_gpio_out_named(from_ref(&self.intrq), "nINT", 1);
+        Ok(())
+    }
+
+    fn gpio_set(&self, line: u32, level: u32) {
+        assert!(line < self.handler_size());
+
+        if self
+            .inner
+            .borrow_mut()
+            .set_input(line, u8::from(level != 0))
+        {
+            self.intrq.raise();
+        }
+    }
+
+    fn handler_size(&self) -> u32 {
+        self.handler.len() as u32
+    }
+
+    fn reset_hold(&self, _type: ResetType) {}
+}
+
+impl_vmstate_struct!(
+    PCF8574Inner,
+    VMStateDescriptionBuilder::<PCF8574Inner>::new()
+        .name(c"pcf8574/inner")
+        .version_id(0)
+        .minimum_version_id(0)
+        .fields(vmstate_fields! {
+            vmstate_of!(PCF8574Inner, lastrq),
+            vmstate_of!(PCF8574Inner, input),
+            vmstate_of!(PCF8574Inner, output),
+        })
+        .build()
+);
+
+pub const VMSTATE_PCF8574: VMStateDescription<PCF8574State> =
+    VMStateDescriptionBuilder::<PCF8574State>::new()
+        .name(c"pcf8574")
+        .version_id(0)
+        .minimum_version_id(0)
+        .fields(vmstate_fields! {
+            vmstate_of!(PCF8574State, parent_obj),
+            vmstate_of!(PCF8574State, inner),
+        })
+        .build();
diff --git a/rust/hw/meson.build b/rust/hw/meson.build
index 9749d4adfc..d6b273170e 100644
--- a/rust/hw/meson.build
+++ b/rust/hw/meson.build
@@ -1,2 +1,3 @@
 subdir('char')
+subdir('gpio')
 subdir('timer')
-- 
2.43.0