[PATCH v14 0/3] rust: add basic serial device bus abstractions

[PATCH v14 0/3] rust: add basic serial device bus abstractions

[Markus Probst]

This patch series adds the serdev device bus rust abstraction into the
kernel.

This abstraction will be used by a driver,
which targets the MCU devices in Synology devices.

Kari Argillander also messaged me, stating that he wants to write a
watchdog driver with this abstraction (needing initial device data).

This series depends on [1].

[1] https://lore.kernel.org/rust-for-linux/20260530132736.3298549-1-dakr@kernel.org/

Signed-off-by: Markus Probst <markus.probst@posteo.de>
---
Changes in v14:
- fix issues reported by Sashiko:
  - fix missing Sync
  - fix write buffers allowed with data.len() > i32::MAX
  - fix sample driver possibly stalling on full tx buffer
- Link to v13: https://patch.msgid.link/20260712-rust_serdev-v13-0-2c4060bc8e30@posteo.de

Changes in v13:
- Added Acked-by trailer from Rob. Consider this a RESEND.
- Link to v12: https://patch.msgid.link/20260603-rust_serdev-v12-0-3400ffb88b12@posteo.de

Changes in v12:
- fix CoreInternal instead of BoundInternal
- Link to v11: https://patch.msgid.link/20260531-rust_serdev-v11-0-dee8e0d830f1@posteo.de

Changes in v11:
- redo changes from v9 with the following fixes:
  - fix memory leak on probe failure
  - fix possible access of dropped drvdata from receive_buf
- Link to v10: https://patch.msgid.link/20260530-rust_serdev-v10-0-65d1d5db876c@posteo.de

Changes in v10:
- revert everything from v9, except BoundInternal
- use mutex to ensure receive_buf won't be called on a dropped drvdata.
- Link to v9: https://patch.msgid.link/20260530-rust_serdev-v9-0-f8b5fccb49c3@posteo.de

Changes in v9:
- make use of BoundInternal
- use PrivateData wrapper and drop rust_private_data field
- use non-devm version of serdev_device_open
- Link to v8: https://patch.msgid.link/20260530-rust_serdev-v8-0-2a95f1da22a7@posteo.de

Changes in v8:
- adapted to driver-lifetime v5 patch series
- add MAINTAINERS file patch
- Link to v7: https://patch.msgid.link/20260429-rust_serdev-v7-0-0d89c791b5c8@posteo.de

Changes in v7:
- adapted to driver-lifetime patch series
- Link to v6: https://patch.msgid.link/20260427-rust_serdev-v6-0-173798d5e1a3@posteo.de

Changes in v6:
- rebased onto v7.1-rc1
- Link to v5: https://patch.msgid.link/20260420-rust_serdev-v5-0-57e8ba0519f3@posteo.de

Changes in v5:
- fix typo in documentation
- Link to v4: https://lore.kernel.org/r/20260411-rust_serdev-v4-0-845e960c6627@posteo.de

Changes in v4:
- fixed not selecting rust serdev abstraction in sample
- Link to v3: https://lore.kernel.org/r/20260313-rust_serdev-v3-0-c9a3af214f7f@posteo.de

Changes in v3:
- fix vertical import style
- add Kconfig entry for the rust abstraction
- fix documentation in include/linux/serdev.h
- rename private_data to rust_private_data
- fix `complete_all` <-> `wait_for_completion` typo
- move drvdata_borrow call after the completion
- Link to v2: https://lore.kernel.org/r/20260306-rust_serdev-v2-0-e9b23b42b255@posteo.de

Changes in v2:
- fix documentation in `serdev::Driver::write` and
  `serdev::Driver::write_all`
- remove use of `dev_info` in probe from the sample
- remove `properties_parse` from the sample
- add optional `baudrate` property to the sample
- remove 1. patch
- remove `TryFrom<&device::Device<Ctx>> for &serdev::Device<Ctx>`
  implementation
- fix import style
- add patch to return reference in `devres::register` to fix safety
  issue
- add patch to add private data to serdev_device, to fix
  `Device.drvdata()` from failing
- simplify abstraction by removing ability to receive the initial
  transmission. It may be added later in a separate patch series if
  needed.
- Link to v1: https://lore.kernel.org/r/20251220-rust_serdev-v1-0-e44645767621@posteo.de

---
Markus Probst (3):
      rust: add basic serial device bus abstractions
      samples: rust: add Rust serial device bus sample device driver
      MAINTAINERS: serdev: Add self for serdev

 MAINTAINERS                        |   5 +-
 drivers/tty/serdev/Kconfig         |   7 +
 rust/bindings/bindings_helper.h    |   1 +
 rust/helpers/helpers.c             |   1 +
 rust/helpers/serdev.c              |  22 ++
 rust/kernel/lib.rs                 |   2 +
 rust/kernel/serdev.rs              | 599 +++++++++++++++++++++++++++++++++++++
 samples/rust/Kconfig               |  11 +
 samples/rust/Makefile              |   1 +
 samples/rust/rust_driver_serdev.rs |  90 ++++++
 10 files changed, 738 insertions(+), 1 deletion(-)
---
base-commit: 1137d8b5df06137fb49513cc923b3b24d94cb809
change-id: 20251217-rust_serdev-ee5481e9085c
prerequisite-message-id: 20260530132736.3298549-1-dakr@kernel.org
prerequisite-patch-id: 310c6bee038ca3909a8e5e58ec12b74f7189b869
prerequisite-patch-id: 92812c3d42b29504838e6dc66c307ff5c035bb5e

[PATCH v14 1/3] rust: add basic serial device bus abstractions

[Markus Probst]

Implement the basic serial device bus abstractions required to write a
serial device bus device driver with or without the need for initial device
data. This includes the following data structures:

The `serdev::Driver` trait represents the interface to the driver.

The `serdev::Device` abstraction represents a `struct serdev_device`.

In order to provide the Serdev specific parts to a generic
`driver::Registration` the `driver::RegistrationOps` trait is
implemented by `serdev::Adapter`.

Signed-off-by: Markus Probst <markus.probst@posteo.de>
---
 MAINTAINERS                     |   2 +
 drivers/tty/serdev/Kconfig      |   7 +
 rust/bindings/bindings_helper.h |   1 +
 rust/helpers/helpers.c          |   1 +
 rust/helpers/serdev.c           |  22 ++
 rust/kernel/lib.rs              |   2 +
 rust/kernel/serdev.rs           | 599 ++++++++++++++++++++++++++++++++++++++++
 7 files changed, 634 insertions(+)

diff --git a/MAINTAINERS b/MAINTAINERS
index 806bd2d80d15..cd735d227892 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -24568,6 +24568,8 @@ S:	Maintained
 F:	Documentation/devicetree/bindings/serial/serial.yaml
 F:	drivers/tty/serdev/
 F:	include/linux/serdev.h
+F:	rust/helpers/serdev.c
+F:	rust/kernel/serdev.rs
 
 SERIAL IR RECEIVER
 M:	Sean Young <sean@mess.org>
diff --git a/drivers/tty/serdev/Kconfig b/drivers/tty/serdev/Kconfig
index 46ae732bfc68..e6dfe949ad01 100644
--- a/drivers/tty/serdev/Kconfig
+++ b/drivers/tty/serdev/Kconfig
@@ -9,6 +9,13 @@ menuconfig SERIAL_DEV_BUS
 
 	  Note that you typically also want to enable TTY port controller support.
 
+config RUST_SERIAL_DEV_BUS_ABSTRACTIONS
+	bool "Rust Serial device bus abstractions"
+	depends on RUST
+	select SERIAL_DEV_BUS
+	help
+	  This enables the Rust abstraction for the serial device bus API.
+
 if SERIAL_DEV_BUS
 
 config SERIAL_DEV_CTRL_TTYPORT
diff --git a/rust/bindings/bindings_helper.h b/rust/bindings/bindings_helper.h
index 1124785e210b..fe7c505da236 100644
--- a/rust/bindings/bindings_helper.h
+++ b/rust/bindings/bindings_helper.h
@@ -85,6 +85,7 @@
 #include <linux/regulator/consumer.h>
 #include <linux/sched.h>
 #include <linux/security.h>
+#include <linux/serdev.h>
 #include <linux/slab.h>
 #include <linux/sys_soc.h>
 #include <linux/task_work.h>
diff --git a/rust/helpers/helpers.c b/rust/helpers/helpers.c
index 998e31052e66..6921a5ecb78a 100644
--- a/rust/helpers/helpers.c
+++ b/rust/helpers/helpers.c
@@ -87,6 +87,7 @@
 #include "regulator.c"
 #include "scatterlist.c"
 #include "security.c"
+#include "serdev.c"
 #include "signal.c"
 #include "slab.c"
 #include "spinlock.c"
diff --git a/rust/helpers/serdev.c b/rust/helpers/serdev.c
new file mode 100644
index 000000000000..c52b78ca3fc7
--- /dev/null
+++ b/rust/helpers/serdev.c
@@ -0,0 +1,22 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <linux/serdev.h>
+
+__rust_helper
+void rust_helper_serdev_device_driver_unregister(struct serdev_device_driver *sdrv)
+{
+	serdev_device_driver_unregister(sdrv);
+}
+
+__rust_helper
+void rust_helper_serdev_device_put(struct serdev_device *serdev)
+{
+	serdev_device_put(serdev);
+}
+
+__rust_helper
+void rust_helper_serdev_device_set_client_ops(struct serdev_device *serdev,
+					      const struct serdev_device_ops *ops)
+{
+	serdev_device_set_client_ops(serdev, ops);
+}
diff --git a/rust/kernel/lib.rs b/rust/kernel/lib.rs
index 9512af7156df..d5ca17336739 100644
--- a/rust/kernel/lib.rs
+++ b/rust/kernel/lib.rs
@@ -119,6 +119,8 @@
 pub mod scatterlist;
 pub mod security;
 pub mod seq_file;
+#[cfg(CONFIG_RUST_SERIAL_DEV_BUS_ABSTRACTIONS)]
+pub mod serdev;
 pub mod sizes;
 #[cfg(CONFIG_SOC_BUS)]
 pub mod soc;
diff --git a/rust/kernel/serdev.rs b/rust/kernel/serdev.rs
new file mode 100644
index 000000000000..0ffcef1849d2
--- /dev/null
+++ b/rust/kernel/serdev.rs
@@ -0,0 +1,599 @@
+// SPDX-License-Identifier: GPL-2.0
+
+//! Abstractions for the serial device bus.
+//!
+//! C header: [`include/linux/serdev.h`](srctree/include/linux/serdev.h)
+
+use crate::{
+    acpi,
+    device,
+    driver,
+    error::{
+        from_result,
+        to_result,
+        VTABLE_DEFAULT_ERROR, //
+    },
+    new_mutex,
+    of,
+    prelude::*,
+    sync::{
+        aref::AlwaysRefCounted,
+        Mutex, //
+    },
+    time::{
+        msecs_to_jiffies,
+        Jiffies,
+        Msecs, //
+    },
+    types::{
+        Opaque,
+        ScopeGuard, //
+    }, //
+};
+
+use core::{
+    cell::UnsafeCell,
+    marker::PhantomData,
+    mem::{offset_of, MaybeUninit},
+    num::NonZero,
+    ptr::NonNull, //
+};
+
+/// Parity bit to use with a serial device.
+#[repr(u32)]
+pub enum Parity {
+    /// No parity bit.
+    None = bindings::serdev_parity_SERDEV_PARITY_NONE,
+    /// Even partiy.
+    Even = bindings::serdev_parity_SERDEV_PARITY_EVEN,
+    /// Odd parity.
+    Odd = bindings::serdev_parity_SERDEV_PARITY_ODD,
+}
+
+/// Timeout in Jiffies.
+pub enum Timeout {
+    /// Wait for a specific amount of [`Jiffies`].
+    Jiffies(NonZero<Jiffies>),
+    /// Wait for a specific amount of [`Msecs`].
+    Milliseconds(NonZero<Msecs>),
+    /// Wait as long as possible.
+    ///
+    /// This is equivalent to [`kernel::task::MAX_SCHEDULE_TIMEOUT`].
+    Max,
+}
+
+impl Timeout {
+    fn into_jiffies(self) -> isize {
+        match self {
+            Self::Jiffies(value) => value.get().try_into().unwrap_or_default(),
+            Self::Milliseconds(value) => {
+                msecs_to_jiffies(value.get()).try_into().unwrap_or_default()
+            }
+            Self::Max => 0,
+        }
+    }
+}
+
+/// An adapter for the registration of serial device bus device drivers.
+pub struct Adapter<T: Driver>(T);
+
+// SAFETY:
+// - `bindings::serdev_device_driver` is a C type declared as `repr(C)`.
+// - `PrivateData<'bound, T>` is the type of the driver's device private data.
+// - `struct serdev_device_driver` embeds a `struct device_driver`.
+// - `DEVICE_DRIVER_OFFSET` is the correct byte offset to the embedded `struct device_driver`.
+unsafe impl<T: Driver> driver::DriverLayout for Adapter<T> {
+    type DriverType = bindings::serdev_device_driver;
+    type DriverData<'bound> = PrivateData<'bound, T>;
+    const DEVICE_DRIVER_OFFSET: usize = core::mem::offset_of!(Self::DriverType, driver);
+}
+
+// SAFETY: A call to `unregister` for a given instance of `DriverType` is guaranteed to be valid if
+// a preceding call to `register` has been successful.
+unsafe impl<T: Driver> driver::RegistrationOps for Adapter<T> {
+    unsafe fn register(
+        sdrv: &Opaque<Self::DriverType>,
+        name: &'static CStr,
+        module: &'static ThisModule,
+    ) -> Result {
+        let of_table = match T::OF_ID_TABLE {
+            Some(table) => table.as_ptr(),
+            None => core::ptr::null(),
+        };
+
+        let acpi_table = match T::ACPI_ID_TABLE {
+            Some(table) => table.as_ptr(),
+            None => core::ptr::null(),
+        };
+
+        // SAFETY: It's safe to set the fields of `struct serdev_device_driver` on initialization.
+        unsafe {
+            (*sdrv.get()).driver.name = name.as_char_ptr();
+            (*sdrv.get()).probe = Some(Self::probe_callback);
+            (*sdrv.get()).remove = Some(Self::remove_callback);
+            (*sdrv.get()).driver.of_match_table = of_table;
+            (*sdrv.get()).driver.acpi_match_table = acpi_table;
+        }
+
+        // SAFETY: `sdrv` is guaranteed to be a valid `DriverType`.
+        to_result(unsafe { bindings::__serdev_device_driver_register(sdrv.get(), module.0) })
+    }
+
+    unsafe fn unregister(sdrv: &Opaque<Self::DriverType>) {
+        // SAFETY: `sdrv` is guaranteed to be a valid `DriverType`.
+        unsafe { bindings::serdev_device_driver_unregister(sdrv.get()) };
+    }
+}
+
+#[doc(hidden)]
+#[pin_data(PinnedDrop)]
+pub struct PrivateData<'bound, T: Driver> {
+    sdev: &'bound Device<device::Bound>,
+    #[pin]
+    driver: UnsafeCell<MaybeUninit<T::Data<'bound>>>,
+    open: UnsafeCell<bool>,
+    #[pin]
+    active: Mutex<bool>,
+}
+
+#[pinned_drop]
+impl<T: Driver> PinnedDrop for PrivateData<'_, T> {
+    fn drop(self: Pin<&mut Self>) {
+        let mut active = self.active.lock();
+        if *active {
+            // SAFETY:
+            // - We have exclusive access to `self.driver`.
+            // - `self.driver` is guaranteed to be initialized.
+            unsafe { (*self.driver.get()).assume_init_drop() };
+            *active = false;
+        }
+        drop(active);
+
+        // SAFETY: We have exclusive access to `self.open`.
+        if unsafe { *self.open.get() } {
+            // SAFETY: `self.sdev.as_raw()` is guaranteed to be a pointer to a valid
+            // `struct serdev_device`.
+            unsafe { bindings::serdev_device_close(self.sdev.as_raw()) };
+        }
+    }
+}
+
+impl<T: Driver> Adapter<T> {
+    const OPS: &'static bindings::serdev_device_ops = &bindings::serdev_device_ops {
+        receive_buf: if T::HAS_RECEIVE {
+            Some(Self::receive_buf_callback)
+        } else {
+            None
+        },
+        write_wakeup: Some(bindings::serdev_device_write_wakeup),
+    };
+
+    extern "C" fn probe_callback(sdev: *mut bindings::serdev_device) -> kernel::ffi::c_int {
+        // SAFETY: The serial device bus only ever calls the probe callback with a valid pointer to
+        // a `struct serdev_device`.
+        //
+        // INVARIANT: `sdev` is valid for the duration of `probe_callback()`.
+        let sdev = unsafe { &*sdev.cast::<Device<device::CoreInternal<'_>>>() };
+        let info = <Self as driver::Adapter>::id_info(sdev.as_ref());
+
+        from_result(|| {
+            sdev.as_ref().set_drvdata(try_pin_init!(PrivateData::<T> {
+                sdev: &**sdev,
+                driver: MaybeUninit::<T::Data<'_>>::zeroed().into(),
+                open: false.into(),
+                active <- new_mutex!(false),
+            }))?;
+            // SAFETY: We just set drvdata to `PrivateData<'_, T>`.
+            let private_data = unsafe { sdev.as_ref().drvdata_borrow::<PrivateData<'_, T>>() };
+            let private_data = ScopeGuard::new_with_data(private_data, |_| {
+                // SAFETY: We just set drvdata to `PrivateData<'_, T>`.
+                drop(unsafe { sdev.as_ref().drvdata_obtain::<PrivateData<'_, T>>() });
+            });
+            let mut active = private_data.active.lock();
+
+            // SAFETY: `sdev.as_raw()` is guaranteed to be a valid pointer to `serdev_device`.
+            unsafe { bindings::serdev_device_set_client_ops(sdev.as_raw(), Self::OPS) };
+
+            // SAFETY: The serial device bus only ever calls the probe callback with a valid pointer
+            // to a `serdev_device`.
+            to_result(unsafe { bindings::serdev_device_open(sdev.as_raw()) })?;
+
+            // SAFETY: We have exclusive access to `private_data.open`.
+            unsafe { *private_data.open.get() = true };
+
+            let data = T::probe(sdev, info);
+
+            // SAFETY: We have exclusive access to `private_data.driver`.
+            let driver = unsafe { &mut *private_data.driver.get() };
+            // SAFETY:
+            // - `driver.as_mut_ptr()` is a valid pointer to uninitialized data.
+            // - `private_data.driver` is pinned.
+            let result = unsafe { data.__pinned_init(driver.as_mut_ptr()) };
+
+            *active = result.is_ok();
+
+            drop(active);
+
+            result.map(|()| {
+                private_data.dismiss();
+                0
+            })
+        })
+    }
+
+    extern "C" fn remove_callback(sdev: *mut bindings::serdev_device) {
+        // SAFETY: The serial device bus only ever calls the remove callback with a valid pointer
+        // to a `struct serdev_device`.
+        //
+        // INVARIANT: `sdev` is valid for the duration of `remove_callback()`.
+        let sdev = unsafe { &*sdev.cast::<Device<device::CoreInternal<'_>>>() };
+
+        // SAFETY: `remove_callback` is only ever called after a successful call to
+        // `probe_callback`, hence it's guaranteed that `Device::set_drvdata()` has been called
+        // and stored a `Pin<KBox<PrivateData<'_, T>>>`.
+        let private_data = unsafe { sdev.as_ref().drvdata_borrow::<PrivateData<'_, T>>() };
+
+        // SAFETY: No one has exclusive access to `private_data.driver`.
+        let data = unsafe { &*private_data.driver.get() };
+        // SAFETY:
+        // - `private_data.driver` is pinned.
+        // - `remove_callback` is only ever called after a successful call to `probe_callback`,
+        //   hence it's guaranteed that `private_data.driver` was initialized.
+        let data_pinned = unsafe { Pin::new_unchecked(data.assume_init_ref()) };
+
+        T::unbind(sdev, data_pinned);
+    }
+
+    extern "C" fn receive_buf_callback(
+        sdev: *mut bindings::serdev_device,
+        buf: *const u8,
+        length: usize,
+    ) -> usize {
+        // SAFETY: The serial device bus only ever calls the receive buf callback with a valid
+        // pointer to a `struct serdev_device`.
+        //
+        // INVARIANT: `sdev` is valid for the duration of `receive_buf_callback()`.
+        let sdev = unsafe { &*sdev.cast::<Device<device::BoundInternal>>() };
+
+        // SAFETY: `receive_buf_callback` is only ever called after a successful call to
+        // `probe_callback`, hence it's guaranteed that `Device::set_drvdata()` has been called
+        // and stored a `Pin<KBox<PrivateData<'_, T>>>`.
+        let private_data = unsafe { sdev.as_ref().drvdata_borrow::<PrivateData<'_, T>>() };
+        let active = private_data.active.lock();
+
+        if !*active {
+            return length;
+        }
+
+        // SAFETY: No one has exclusive access to `private_data.driver`.
+        let data = unsafe { &*private_data.driver.get() };
+        // SAFETY:
+        // - `private_data.driver` is pinned.
+        // - `receive_buf_callback` is only ever called after a successful call to `probe_callback`,
+        //   hence it's guaranteed that `private_data.driver` was initialized.
+        let data_pinned = unsafe { Pin::new_unchecked(data.assume_init_ref()) };
+
+        // SAFETY: `buf` is guaranteed to be non-null and has the size of `length`.
+        let buf = unsafe { core::slice::from_raw_parts(buf, length) };
+
+        T::receive(sdev, data_pinned, buf)
+    }
+}
+
+impl<T: Driver> driver::Adapter for Adapter<T> {
+    type IdInfo = T::IdInfo;
+
+    fn of_id_table() -> Option<of::IdTable<Self::IdInfo>> {
+        T::OF_ID_TABLE
+    }
+
+    fn acpi_id_table() -> Option<acpi::IdTable<Self::IdInfo>> {
+        T::ACPI_ID_TABLE
+    }
+}
+
+/// Declares a kernel module that exposes a single serial device bus device driver.
+///
+/// # Examples
+///
+/// ```ignore
+/// kernel::module_serdev_device_driver! {
+///     type: MyDriver,
+///     name: "Module name",
+///     authors: ["Author name"],
+///     description: "Description",
+///     license: "GPL v2",
+/// }
+/// ```
+#[macro_export]
+macro_rules! module_serdev_device_driver {
+    ($($f:tt)*) => {
+        $crate::module_driver!(<T>, $crate::serdev::Adapter<T>, { $($f)* });
+    };
+}
+
+/// The serial device bus device driver trait.
+///
+/// Drivers must implement this trait in order to get a serial device bus device driver registered.
+///
+/// # Examples
+///
+///```
+/// # use kernel::{
+///     acpi,
+///     bindings,
+///     device::{
+///         Bound,
+///         Core, //
+///     },
+///     of,
+///     serdev, //
+/// };
+///
+/// struct MyDriver;
+///
+/// kernel::of_device_table!(
+///     OF_TABLE,
+///     MODULE_OF_TABLE,
+///     <MyDriver as serdev::Driver>::IdInfo,
+///     [
+///         (of::DeviceId::new(c"test,device"), ())
+///     ]
+/// );
+///
+/// kernel::acpi_device_table!(
+///     ACPI_TABLE,
+///     MODULE_ACPI_TABLE,
+///     <MyDriver as serdev::Driver>::IdInfo,
+///     [
+///         (acpi::DeviceId::new(c"LNUXBEEF"), ())
+///     ]
+/// );
+///
+/// #[vtable]
+/// impl serdev::Driver for MyDriver {
+///     type IdInfo = ();
+///     type Data<'bound> = Self;
+///     const OF_ID_TABLE: Option<of::IdTable<Self::IdInfo>> = Some(&OF_TABLE);
+///     const ACPI_ID_TABLE: Option<acpi::IdTable<Self::IdInfo>> = Some(&ACPI_TABLE);
+///
+///     fn probe<'bound>(
+///         sdev: &'bound serdev::Device<Core<'_>>,
+///         _id_info: Option<&'bound Self::IdInfo>,
+///     ) -> impl PinInit<Self::Data<'bound>, Error> + 'bound {
+///         sdev.set_baudrate(115200);
+///         sdev.write_all(b"Hello\n", serdev::Timeout::Max)?;
+///         Ok(MyDriver)
+///     }
+/// }
+///```
+#[vtable]
+pub trait Driver {
+    /// The type holding driver private data about each device id supported by the driver.
+    // TODO: Use associated_type_defaults once stabilized:
+    //
+    // ```
+    // type IdInfo: 'static = ();
+    // ```
+    type IdInfo: 'static;
+
+    /// The type of the driver's bus device private data.
+    type Data<'bound>: Send + Sync + 'bound;
+
+    /// The table of OF device ids supported by the driver.
+    const OF_ID_TABLE: Option<of::IdTable<Self::IdInfo>> = None;
+
+    /// The table of ACPI device ids supported by the driver.
+    const ACPI_ID_TABLE: Option<acpi::IdTable<Self::IdInfo>> = None;
+
+    /// Serial device bus device driver probe.
+    ///
+    /// Called when a new serial device bus device is added or discovered.
+    /// Implementers should attempt to initialize the device here.
+    fn probe<'bound>(
+        sdev: &'bound Device<device::Core<'_>>,
+        id_info: Option<&'bound Self::IdInfo>,
+    ) -> impl PinInit<Self::Data<'bound>, Error> + 'bound;
+
+    /// Serial device bus device driver unbind.
+    ///
+    /// Called when a [`Device`] is unbound from its bound [`Driver`]. Implementing this callback
+    /// is optional.
+    ///
+    /// This callback serves as a place for drivers to perform teardown operations that require a
+    /// `&Device<Core>` or `&Device<Bound>` reference. For instance.
+    ///
+    /// Otherwise, release operations for driver resources should be performed in `Drop`.
+    fn unbind<'bound>(sdev: &'bound Device<device::Core<'_>>, this: Pin<&Self::Data<'bound>>) {
+        let _ = (sdev, this);
+    }
+
+    /// Serial device bus device data receive callback.
+    ///
+    /// Called when data got received from device.
+    ///
+    /// Returns the number of bytes accepted.
+    fn receive<'bound>(
+        sdev: &'bound Device<device::Bound>,
+        this: Pin<&Self::Data<'bound>>,
+        data: &[u8],
+    ) -> usize {
+        let _ = (sdev, this, data);
+        build_error!(VTABLE_DEFAULT_ERROR)
+    }
+}
+
+/// The serial device bus device representation.
+///
+/// This structure represents the Rust abstraction for a C `struct serdev_device`. The
+/// implementation abstracts the usage of an already existing C `struct serdev_device` within Rust
+/// code that we get passed from the C side.
+///
+/// # Invariants
+///
+/// A [`Device`] instance represents a valid `struct serdev_device` created by the C portion of
+/// the kernel.
+#[repr(transparent)]
+pub struct Device<Ctx: device::DeviceContext = device::Normal>(
+    Opaque<bindings::serdev_device>,
+    PhantomData<Ctx>,
+);
+
+impl<Ctx: device::DeviceContext> Device<Ctx> {
+    fn as_raw(&self) -> *mut bindings::serdev_device {
+        self.0.get()
+    }
+}
+
+impl Device<device::Bound> {
+    /// Set the baudrate in bits per second.
+    ///
+    /// Common baudrates are 115200, 9600, 19200, 57600, 4800.
+    ///
+    /// Use [`Device::write_flush`] before calling this if you have written data prior to this call.
+    pub fn set_baudrate(&self, speed: u32) -> Result<(), u32> {
+        // SAFETY: `self.as_raw()` is guaranteed to be a pointer to a valid `serdev_device`.
+        let ret = unsafe { bindings::serdev_device_set_baudrate(self.as_raw(), speed) };
+        if ret == speed {
+            Ok(())
+        } else {
+            Err(ret)
+        }
+    }
+
+    /// Set if flow control should be enabled.
+    ///
+    /// Use [`Device::write_flush`] before calling this if you have written data prior to this call.
+    pub fn set_flow_control(&self, enable: bool) {
+        // SAFETY: `self.as_raw()` is guaranteed to be a pointer to a valid `serdev_device`.
+        unsafe { bindings::serdev_device_set_flow_control(self.as_raw(), enable) };
+    }
+
+    /// Set parity to use.
+    ///
+    /// Use [`Device::write_flush`] before calling this if you have written data prior to this call.
+    pub fn set_parity(&self, parity: Parity) -> Result {
+        // SAFETY: `self.as_raw()` is guaranteed to be a pointer to a valid `serdev_device`.
+        to_result(unsafe { bindings::serdev_device_set_parity(self.as_raw(), parity as u32) })
+    }
+
+    /// Write data to the serial device until the controller has accepted all the data or has
+    /// been interrupted by a timeout or signal.
+    ///
+    /// Note that any accepted data has only been buffered by the controller. Use
+    /// [`Device::wait_until_sent`] to make sure the controller write buffer has actually been
+    /// emptied.
+    ///
+    /// Returns the number of bytes written (less than `data.len()` if interrupted).
+    /// [`kernel::error::code::ETIMEDOUT`] or [`kernel::error::code::ERESTARTSYS`] if interrupted
+    /// before any bytes were written.
+    pub fn write_all(&self, data: &[u8], timeout: Timeout) -> Result<usize> {
+        if data.len() > i32::MAX as usize {
+            return Err(EINVAL);
+        }
+
+        // SAFETY:
+        // - `self.as_raw()` is guaranteed to be a pointer to a valid `serdev_device`.
+        // - `data.as_ptr()` is guaranteed to be a valid array pointer with the size of
+        //   `data.len()`.
+        let ret = unsafe {
+            bindings::serdev_device_write(
+                self.as_raw(),
+                data.as_ptr(),
+                data.len(),
+                timeout.into_jiffies(),
+            )
+        };
+        // CAST: negative return values are guaranteed to be between `-MAX_ERRNO` and `-1`,
+        // which always fit into a `i32`.
+        to_result(ret as i32).map(|()| ret.unsigned_abs())
+    }
+
+    /// Write data to the serial device.
+    ///
+    /// If you want to write until the controller has accepted all the data, use
+    /// [`Device::write_all`].
+    ///
+    /// Note that any accepted data has only been buffered by the controller. Use
+    /// [ Device::wait_until_sent`] to make sure the controller write buffer has actually been
+    /// emptied.
+    ///
+    /// Returns the number of bytes written (less than `data.len()` if not enough room in the
+    /// write buffer).
+    pub fn write(&self, data: &[u8]) -> Result<u32> {
+        if data.len() > i32::MAX as usize {
+            return Err(EINVAL);
+        }
+
+        // SAFETY:
+        // - `self.as_raw()` is guaranteed to be a pointer to a valid `serdev_device`.
+        // - `data.as_ptr()` is guaranteed to be a valid array pointer with the size of
+        //   `data.len()`.
+        let ret =
+            unsafe { bindings::serdev_device_write_buf(self.as_raw(), data.as_ptr(), data.len()) };
+
+        to_result(ret as i32).map(|()| ret.unsigned_abs())
+    }
+
+    /// Send data to the serial device immediately.
+    ///
+    /// Note that this doesn't guarantee that the data has been transmitted.
+    /// Use [`Device::wait_until_sent`] for this purpose.
+    pub fn write_flush(&self) {
+        // SAFETY: `self.as_raw()` is guaranteed to be a pointer to a valid `serdev_device`.
+        unsafe { bindings::serdev_device_write_flush(self.as_raw()) };
+    }
+
+    /// Wait for the data to be sent.
+    ///
+    /// After this function, the write buffer of the controller should be empty.
+    pub fn wait_until_sent(&self, timeout: Timeout) {
+        // SAFETY: `self.as_raw()` is guaranteed to be a pointer to a valid `serdev_device`.
+        unsafe { bindings::serdev_device_wait_until_sent(self.as_raw(), timeout.into_jiffies()) };
+    }
+}
+
+// SAFETY: `serdev::Device` is a transparent wrapper of `struct serdev_device`.
+// The offset is guaranteed to point to a valid device field inside `serdev::Device`.
+unsafe impl<Ctx: device::DeviceContext> device::AsBusDevice<Ctx> for Device<Ctx> {
+    const OFFSET: usize = offset_of!(bindings::serdev_device, dev);
+}
+
+// SAFETY: `Device` is a transparent wrapper of a type that doesn't depend on `Device`'s generic
+// argument.
+kernel::impl_device_context_deref!(unsafe { Device });
+kernel::impl_device_context_into_aref!(Device);
+
+// SAFETY: Instances of `Device` are always reference-counted.
+unsafe impl AlwaysRefCounted for Device {
+    fn inc_ref(&self) {
+        self.as_ref().inc_ref();
+    }
+
+    unsafe fn dec_ref(obj: NonNull<Self>) {
+        // SAFETY: The safety requirements guarantee that the refcount is non-zero.
+        unsafe { bindings::serdev_device_put(obj.cast().as_ptr()) }
+    }
+}
+
+impl<Ctx: device::DeviceContext> AsRef<device::Device<Ctx>> for Device<Ctx> {
+    fn as_ref(&self) -> &device::Device<Ctx> {
+        // SAFETY: By the type invariant of `Self`, `self.as_raw()` is a pointer to a valid
+        // `struct serdev_device`.
+        let dev = unsafe { &raw mut (*self.as_raw()).dev };
+
+        // SAFETY: `dev` points to a valid `struct device`.
+        unsafe { device::Device::from_raw(dev) }
+    }
+}
+
+// SAFETY: A `Device` is always reference-counted and can be released from any thread.
+unsafe impl Send for Device {}
+
+// SAFETY: `Device` can be shared among threads because all methods of `Device`
+// (i.e. `Device<Normal>) are thread safe.
+unsafe impl Sync for Device {}
+
+// SAFETY: Same as `Device<Normal>` -- the underlying `struct serdev_device` is the same;
+// `Bound` is a zero-sized type-state marker that does not affect thread safety.
+unsafe impl Sync for Device<device::Bound> {}

-- 
2.54.0

[PATCH v14 2/3] samples: rust: add Rust serial device bus sample device driver

[Markus Probst]

Add a sample Rust serial device bus device driver illustrating the usage
of the serial device bus abstractions.

This drivers probes through either a match of device / driver name or a
match within the OF ID table.

Signed-off-by: Markus Probst <markus.probst@posteo.de>
---
 MAINTAINERS                        |  1 +
 samples/rust/Kconfig               | 11 +++++
 samples/rust/Makefile              |  1 +
 samples/rust/rust_driver_serdev.rs | 90 ++++++++++++++++++++++++++++++++++++++
 4 files changed, 103 insertions(+)

diff --git a/MAINTAINERS b/MAINTAINERS
index cd735d227892..7d32aa7f42a4 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -24570,6 +24570,7 @@ F:	drivers/tty/serdev/
 F:	include/linux/serdev.h
 F:	rust/helpers/serdev.c
 F:	rust/kernel/serdev.rs
+F:	samples/rust/rust_driver_serdev.rs
 
 SERIAL IR RECEIVER
 M:	Sean Young <sean@mess.org>
diff --git a/samples/rust/Kconfig b/samples/rust/Kconfig
index c49ab9106345..31d62533ef25 100644
--- a/samples/rust/Kconfig
+++ b/samples/rust/Kconfig
@@ -161,6 +161,17 @@ config SAMPLE_RUST_DRIVER_AUXILIARY
 
 	  If unsure, say N.
 
+config SAMPLE_RUST_DRIVER_SERDEV
+	tristate "Serial Device Bus Device Driver"
+	select RUST_SERIAL_DEV_BUS_ABSTRACTIONS
+	help
+	  This option builds the Rust serial device bus driver sample.
+
+	  To compile this as a module, choose M here:
+	  the module will be called rust_driver_serdev.
+
+	  If unsure, say N.
+
 config SAMPLE_RUST_SOC
 	tristate "SoC Driver"
 	select SOC_BUS
diff --git a/samples/rust/Makefile b/samples/rust/Makefile
index 6c0aaa58cccc..b986b681cde5 100644
--- a/samples/rust/Makefile
+++ b/samples/rust/Makefile
@@ -14,6 +14,7 @@ obj-$(CONFIG_SAMPLE_RUST_DRIVER_PLATFORM)	+= rust_driver_platform.o
 obj-$(CONFIG_SAMPLE_RUST_DRIVER_USB)		+= rust_driver_usb.o
 obj-$(CONFIG_SAMPLE_RUST_DRIVER_FAUX)		+= rust_driver_faux.o
 obj-$(CONFIG_SAMPLE_RUST_DRIVER_AUXILIARY)	+= rust_driver_auxiliary.o
+obj-$(CONFIG_SAMPLE_RUST_DRIVER_SERDEV)		+= rust_driver_serdev.o
 obj-$(CONFIG_SAMPLE_RUST_CONFIGFS)		+= rust_configfs.o
 obj-$(CONFIG_SAMPLE_RUST_SOC)			+= rust_soc.o
 
diff --git a/samples/rust/rust_driver_serdev.rs b/samples/rust/rust_driver_serdev.rs
new file mode 100644
index 000000000000..a12b1412db30
--- /dev/null
+++ b/samples/rust/rust_driver_serdev.rs
@@ -0,0 +1,90 @@
+// SPDX-License-Identifier: GPL-2.0
+
+//! Rust Serial device bus device driver sample.
+
+use kernel::{
+    acpi,
+    device::{
+        Bound,
+        Core, //
+    },
+    of,
+    prelude::*,
+    serdev,
+    sync::aref::ARef, //
+};
+
+struct SampleDriver {
+    sdev: ARef<serdev::Device>,
+}
+
+kernel::of_device_table!(
+    OF_TABLE,
+    MODULE_OF_TABLE,
+    <SampleDriver as serdev::Driver>::IdInfo,
+    [(of::DeviceId::new(c"test,rust_driver_serdev"), ())]
+);
+
+kernel::acpi_device_table!(
+    ACPI_TABLE,
+    MODULE_ACPI_TABLE,
+    <SampleDriver as serdev::Driver>::IdInfo,
+    [(acpi::DeviceId::new(c"LNUXBEEF"), ())]
+);
+
+#[vtable]
+impl serdev::Driver for SampleDriver {
+    type IdInfo = ();
+    type Data<'bound> = Self;
+    const OF_ID_TABLE: Option<of::IdTable<Self::IdInfo>> = Some(&OF_TABLE);
+    const ACPI_ID_TABLE: Option<acpi::IdTable<Self::IdInfo>> = Some(&ACPI_TABLE);
+
+    fn probe<'bound>(
+        sdev: &'bound serdev::Device<Core<'_>>,
+        _info: Option<&'bound Self::IdInfo>,
+    ) -> impl PinInit<Self, Error> + 'bound {
+        let dev = sdev.as_ref();
+
+        dev_dbg!(dev, "Probe Rust Serial device bus device driver sample.\n");
+
+        if sdev
+            .set_baudrate(
+                dev.fwnode()
+                    .and_then(|fwnode| fwnode.property_read(c"baudrate").optional())
+                    .unwrap_or(115200),
+            )
+            .is_err()
+        {
+            return Err(EINVAL);
+        }
+        sdev.set_flow_control(false);
+        sdev.set_parity(serdev::Parity::None)?;
+
+        Ok(Self { sdev: sdev.into() })
+    }
+
+    fn receive<'bound>(
+        sdev: &'bound serdev::Device<Bound>,
+        _this: Pin<&Self>,
+        data: &[u8],
+    ) -> usize {
+        sdev.write(data).unwrap_or_default() as usize
+    }
+}
+
+impl Drop for SampleDriver {
+    fn drop(&mut self) {
+        dev_dbg!(
+            self.sdev.as_ref(),
+            "Remove Rust Serial device bus device driver sample.\n"
+        );
+    }
+}
+
+kernel::module_serdev_device_driver! {
+    type: SampleDriver,
+    name: "rust_driver_serdev",
+    authors: ["Markus Probst"],
+    description: "Rust Serial device bus device driver",
+    license: "GPL v2",
+}

-- 
2.54.0

[PATCH v14 3/3] MAINTAINERS: serdev: Add self for serdev

[Markus Probst]

Rob mentioned he needs to find someone else to maintain serdev.

Link: https://lore.kernel.org/rust-for-linux/20260430195858.GA1650658-robh@kernel.org/
Link: https://lore.kernel.org/rust-for-linux/da85ceb81f51079d4a8248a1ffde6a27d2ef24ad.camel@posteo.de/
Acked-by: Rob Herring (Arm) <robh@kernel.org>
Signed-off-by: Markus Probst <markus.probst@posteo.de>
---
 MAINTAINERS | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/MAINTAINERS b/MAINTAINERS
index 7d32aa7f42a4..d092042fed31 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -24562,7 +24562,7 @@ F:	drivers/iio/chemical/sps30_i2c.c
 F:	drivers/iio/chemical/sps30_serial.c
 
 SERIAL DEVICE BUS
-M:	Rob Herring <robh@kernel.org>
+M:	Markus Probst <markus.probst@posteo.de>
 L:	linux-serial@vger.kernel.org
 S:	Maintained
 F:	Documentation/devicetree/bindings/serial/serial.yaml

-- 
2.54.0

Re: [PATCH v14 1/3] rust: add basic serial device bus abstractions

[sashiko-bot]

Thank you for your contribution! Sashiko AI review found 3 potential issue(s) to consider:
- [High] Drivers cannot synchronously wait for data during `probe` without causing a deadlock, because `receive_buf_callback` blocks on a mutex held by `probe_callback`.
- [High] Concurrent device callbacks during unbind or probe failure lead to Use-After-Free (UAF) or NULL pointer dereference because driver data is cleared before the device is closed.
- [High] `Device::set_baudrate` incorrectly treats approximate baudrates as errors, which will fail driver initialization on many hardware platforms.
--

--- Patch [1]: [PATCH v14 1/3] rust: add basic serial device bus abstractions ---
Note: The format of this review is altered to provide a free-form summary of
the findings, rather than inline diff comments, due to system recitation
restrictions.

commit c091dc3bf08c045ff86b0afe5e41d3fd0a94bb83
Author: Markus Probst <markus.probst@posteo.de>
Subject: rust: add basic serial device bus abstractions

Implement the basic serial device bus abstractions required to write a
serial device bus device driver.

[Severity: High]
In Adapter<T>::probe_callback(), the code acquires the active mutex and
holds it across serdev_device_open() and data.__pinned_init(). If a driver
needs to send a command to the device and synchronously wait for a response
during its probe routine, won't this cause a deadlock?

When the device responds, Adapter<T>::receive_buf_callback() is invoked in
the RX workqueue and attempts to lock the exact same active mutex. Since
probe_callback() is blocked waiting for the response, and
receive_buf_callback() is blocked waiting for the mutex, the system seems
like it will deadlock. Is it possible to unlock before waiting, or use a
different synchronization strategy?

[Severity: High]
Looking at Adapter<T>::remove_callback(), it appears that T::unbind() is
called, but PrivateData is never explicitly dropped or obtained from the
device data, which might leave the device open and leak memory.

When remove_callback() returns, the C driver core sets drvdata to NULL. If
data arrives immediately after, receive_buf_callback() might read a NULL
pointer from drvdata_borrow() and dereference it.

Similarly, on a probe error in Adapter<T>::probe_callback(), ScopeGuard
clears drvdata before PrivateData's PinnedDrop implementation closes the
device. Does this create a race window where the device is still open and
receiving data while drvdata is NULL or in the process of being destroyed?

[Severity: High]
In Device::set_baudrate(), the success condition is checked using strict
equality (ret == speed).

Since serdev_device_set_baudrate() configures the hardware and returns the
actual achieved baudrate (or 0 on failure), hardware clock divider
limitations often result in a baudrate that is close but not exactly equal
to the requested speed (for example, returning 115198 when 115200 is
requested).

Will this strict equality check cause valid driver initializations to fail
on platforms that can only approximate the requested baudrate?

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260715-rust_serdev-v14-0-b4ed5c93606f@posteo.de?part=1

Re: [PATCH v14 2/3] samples: rust: add Rust serial device bus sample device driver

[sashiko-bot]

Thank you for your contribution! Sashiko AI review found 4 potential issue(s) to consider:
- [High] The `remove_callback` function in the Rust `serdev` abstraction fails to free the driver's private data (`PrivateData`), leading to a memory leak when the device is unbound.
- [Medium] The `receive` callback returns the number of bytes written to the Tx buffer rather than the number of bytes consumed from the Rx buffer, which can permanently stall the TTY Rx path.
- [Low] The driver queries the non-standard device tree property `baudrate` instead of the standard `current-speed` to configure the serial speed.
- [Low] The driver registers an ACPI ID table but this behavior is entirely omitted from the commit message.
--

--- Patch [2]: [PATCH v14 2/3] samples: rust: add Rust serial device bus sample device driver ---
commit 119f675ea28625315fe04a8ca0cdd59f9d0f26bc
Author: Markus Probst <markus.probst@posteo.de>

samples: rust: add Rust serial device bus sample device driver
    
Add a sample Rust serial device bus device driver illustrating the usage
of the serial device bus abstractions.

> This drivers probes through either a match of device / driver name or a
> match within the OF ID table.

[Severity: Low]
Does this description omit the ACPI ID table?

Looking at ACPI_TABLE in rust_driver_serdev.rs, the driver also registers an
ACPI ID table for matching:

kernel::acpi_device_table!(
    ACPI_TABLE,
    MODULE_ACPI_TABLE,
    <SampleDriver as serdev::Driver>::IdInfo,
    [(acpi::DeviceId::new(c"LNUXBEEF"), ())]
);

Could the commit message be updated to mention the ACPI matching behavior as
well?

> diff --git a/samples/rust/rust_driver_serdev.rs b/samples/rust/rust_driver_serdev.rs
> new file mode 100644
> index 0000000000000..a12b1412db30c
> --- /dev/null
> +++ b/samples/rust/rust_driver_serdev.rs
> @@ -0,0 +1,90 @@
[ ... ]
> +    fn probe<'bound>(
> +        sdev: &'bound serdev::Device<Core<'_>>,
> +        _info: Option<&'bound Self::IdInfo>,
> +    ) -> impl PinInit<Self, Error> + 'bound {
> +        let dev = sdev.as_ref();
> +
> +        dev_dbg!(dev, "Probe Rust Serial device bus device driver sample.\n");
> +
> +        if sdev
> +            .set_baudrate(
> +                dev.fwnode()
> +                    .and_then(|fwnode| fwnode.property_read(c"baudrate").optional())

[Severity: Low]
Does this code use an incorrect, non-standard device tree property?

It looks like it queries c"baudrate" instead of the standard c"current-speed"
property, which could cause it to fail to configure the speed on platforms
compliant with standard bindings.

> +                    .unwrap_or(115200),
> +            )
> +            .is_err()
> +        {
> +            return Err(EINVAL);
> +        }
> +        sdev.set_flow_control(false);
> +        sdev.set_parity(serdev::Parity::None)?;
> +
> +        Ok(Self { sdev: sdev.into() })
> +    }
> +
> +    fn receive<'bound>(
> +        sdev: &'bound serdev::Device<Bound>,
> +        _this: Pin<&Self>,
> +        data: &[u8],
> +    ) -> usize {
> +        sdev.write(data).unwrap_or_default() as usize

[Severity: Medium]
Could this permanently stall the TTY Rx path?

The receive callback appears to return the number of bytes written to the
Tx buffer rather than the number of bytes consumed from the Rx buffer.

If the Tx buffer is full, sdev.write() returns 0, and the TTY layer will
stop pushing data. Without a mechanism to wake up the Rx path when Tx space
becomes available, does this permanently stall the receiver?

> +    }
> +}

I also noticed an issue in rust/kernel/serdev.rs during driver unbind:

rust/kernel/serdev.rs:remove_callback() {
    ...
    let private_data = unsafe { sdev.as_ref().drvdata_borrow::<PrivateData<'_, T>>() };

    // SAFETY: No one has exclusive access to private_data.driver.
    let data = unsafe { &*private_data.driver.get() };
    ...
    T::unbind(sdev, data_pinned);
}

[Severity: High]
Does this code leak the driver's private data?

The remove_callback() function appears to fail to free PrivateData because it
uses drvdata_borrow() instead of drvdata_obtain() on the teardown path, which
would take ownership back and allow the driver data allocation to be dropped
when the device is unbound.

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260715-rust_serdev-v14-0-b4ed5c93606f@posteo.de?part=2