On Sat, Oct 25, 2025 at 12:38:50PM +0000, chenmiao wrote: > Date: Sat, 25 Oct 2025 12:38:50 +0000 > From: chenmiao <[email protected]> > Subject: [RFC 2/5] rust: hw: core: Add rust bindings/funcs for i2c bus > X-Mailer: git-send-email 2.43.0 > > 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 <[email protected]> > Signed-off-by: chenmiao <[email protected]> > --- > rust/hw/core/meson.build | 1 + > rust/hw/core/src/i2cbus.rs | 291 +++++++++++++++++++++++++++++++++++++ > rust/hw/core/src/lib.rs | 3 + > rust/hw/core/wrapper.h | 1 + > 4 files changed, 296 insertions(+) > create mode 100644 rust/hw/core/src/i2cbus.rs > > diff --git a/rust/hw/core/meson.build b/rust/hw/core/meson.build > index efcda50..7c44786 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/i2cbus.rs', > 'src/qdev.rs', > 'src/sysbus.rs', > ], > diff --git a/rust/hw/core/src/i2cbus.rs b/rust/hw/core/src/i2cbus.rs > new file mode 100644 > index 0000000..c026955 > --- /dev/null > +++ b/rust/hw/core/src/i2cbus.rs
This file implements both I2CBus and I2C device (Slave). To be general, I think it's better to name it as "i2c.rs". > @@ -0,0 +1,291 @@ > +// Copyright 2025 HUST OpenAtom Open Source Club. > +// Author(s): Chao Liu <[email protected]> > +// Author(s): Chen Miao <[email protected]> > +// SPDX-License-Identifier: GPL-2.0-or-later > + > +//! Bindings to access `i2c` functionality from Rust. > + > +use std::ffi::CStr; > + > +pub use bindings::I2CSlaveClass; > +use common::Opaque; > +use qom::{prelude::*, Owned}; > +use util::Result; > + > +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); > + > +// TODO: add virtual methods > +pub trait I2CBusImpl: DeviceImpl + IsA<I2CBus> {} > + > +/// Trait for methods of [`I2CBus`] and its subclasses. > +pub trait I2CBusMethods: ObjectDeref > +where > + Self::Target: IsA<I2CBus>, > +{ > + /// Initialize an I2C bus > + fn init_bus(&self, parent: &DeviceState, name: &str) -> *mut > bindings::I2CBus { > + assert!(bql::is_locked()); It's better to add # SFAETY comment (others methods below also need it). > + unsafe { bindings::i2c_init_bus(parent.as_mut_ptr(), > name.as_ptr().cast()) } > + } ... > + /// 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. > + unsafe fn set_master(&self, bh: *mut bindings::QEMUBH) { I think it's better to have a Opaque<> wrapper over bindings::QEMUBH. However, async has not yet been fully considered. IMO, It seems i2c_bus_master() is only used by i2c-echo, which is not implememnted in this series. Perhaps this series could initially omit QEMUBH (with a TODO comment) until QEMUBH binding is introduced. > + assert!(bql::is_locked()); > + unsafe { bindings::i2c_bus_master(self.upcast().as_mut_ptr(), bh) } > + } > + > + /// Release an I2C bus > + fn release(&self) { > + assert!(bql::is_locked()); > + unsafe { bindings::i2c_bus_release(self.upcast().as_mut_ptr()) } > + } > +} > + > +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); > + > +// 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) -> Result<bool>> = None; > + > + /// Master to slave (asynchronous). Receiving slave must call > `i2c_ack()`. > + const SEND_ASYNC: Option<fn(&Self, data: u8) -> Result<()>> = None; > + > + /// Slave to master. This cannot fail, the device should always return > something here. > + const RECV: Option<fn(&Self) -> Result<bool>> = 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) -> Result<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. > + type AddressMatcher; > + const MATCH_AND_ADD: Option<Self::AddressMatcher> = None; > +} > + > +impl I2CSlaveClass { > + /// Fill in the virtual methods of `I2CSlaveClass` based on the > + /// definitions in the `I2CSlaveImpl` trait. > + pub fn class_init<T: I2CSlaveImpl>(self: &mut I2CSlaveClass) { It seems the callbacks (SEND/SEND_ASYNC/...) are missing to set here. For example, add a callback wrapper first: unsafe extern "C" fn rust_i2c_slave_send_fn<T: I2CSlaveImpl>( slave: *mut bindings::I2CSlave, date: u8, ) { let state = NonNull::new(slave).unwrap().cast::<T>(); T::SEND.unwrap()(unsafe { state.as_ref() }, data); } Then create C callback like: pub fn class_init<T: I2CSlaveImpl>(self: &mut I2CSlaveClass) { ... if <T as I2CSlaveImpl>::SEND.is_some() { self.send = Some(rust_i2c_slave_send_fn::<T>); } ... } Similarly, you can refer to ResettableClass::class_init and DeviceClass::class_init. > + self.parent_class.class_init::<T>(); > + } > +} > + Regards, Zhao
