Claude review: rust: add basic serial device bus abstractions

Claude review: rust: add basic serial device bus abstractions

[Claude Code Review Bot]

Overall Series Review

Subject: rust: add basic serial device bus abstractions
Author: Markus Probst <markus.probst@posteo.de>
Patches: 11
Reviewed: 2026-03-09T08:21:39.224101

---

This is a v2 series adding Rust abstractions for the serial device bus (serdev) subsystem, comprising a devres change, a C-side struct addition, the main Rust abstraction, and a sample driver. The overall structure and intent is good -- having a Rust serdev abstraction follows the same pattern as other bus drivers (platform, USB, auxiliary). However, there are several **critical soundness and correctness issues** that must be addressed before this can be merged, including a double-free, a use-after-null/UB race condition, and a broken timeout value.

---

---
Generated by Claude Code Patch Reviewer

[PATCH v3 0/4] 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).

@Rob: Are you willing to maintain these rust abstractions yourself,
as you are the expert on this subsystem, otherwise I would take care of
it with a "SERIAL DEVICE BUS [RUST]" section in the MAINTAINERS file. In
the second case, I assume you are going to pick those patches as-is into
your tree, after they have been reviewed?

Signed-off-by: Markus Probst <markus.probst@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 (4):
      rust: devres: return reference in `devres::register`
      serdev: add rust private data to serdev_device
      rust: add basic serial device bus abstractions
      samples: rust: add Rust serial device bus sample device driver

 drivers/tty/serdev/Kconfig         |   7 +
 include/linux/serdev.h             |  15 +-
 rust/bindings/bindings_helper.h    |   1 +
 rust/helpers/helpers.c             |   1 +
 rust/helpers/serdev.c              |  22 ++
 rust/kernel/cpufreq.rs             |   3 +-
 rust/kernel/devres.rs              |  15 +-
 rust/kernel/drm/driver.rs          |   3 +-
 rust/kernel/lib.rs                 |   2 +
 rust/kernel/serdev.rs              | 536 +++++++++++++++++++++++++++++++++++++
 samples/rust/Kconfig               |  11 +
 samples/rust/Makefile              |   1 +
 samples/rust/rust_driver_serdev.rs |  86 ++++++
 13 files changed, 693 insertions(+), 10 deletions(-)
---
base-commit: 1f318b96cc84d7c2ab792fcc0bfd42a7ca890681
change-id: 20251217-rust_serdev-ee5481e9085c

[PATCH v3 1/4] rust: devres: return reference in `devres::register`

[Markus Probst]

Return the reference to the initialized data in the `devres::register`
function.

This is needed in a following commit (rust: add basic serial device bus
abstractions).

Signed-off-by: Markus Probst <markus.probst@posteo.de>
---
 rust/kernel/cpufreq.rs    |  3 ++-
 rust/kernel/devres.rs     | 15 +++++++++++++--
 rust/kernel/drm/driver.rs |  3 ++-
 3 files changed, 17 insertions(+), 4 deletions(-)

diff --git a/rust/kernel/cpufreq.rs b/rust/kernel/cpufreq.rs
index 76faa1ac8501..8cf86bb8e0f4 100644
--- a/rust/kernel/cpufreq.rs
+++ b/rust/kernel/cpufreq.rs
@@ -1051,7 +1051,8 @@ pub fn new_foreign_owned(dev: &Device<Bound>) -> Result
     where
         T: 'static,
     {
-        devres::register(dev, Self::new()?, GFP_KERNEL)
+        devres::register(dev, Self::new()?, GFP_KERNEL)?;
+        Ok(())
     }
 }
 
diff --git a/rust/kernel/devres.rs b/rust/kernel/devres.rs
index 6afe196be42c..f882bace8601 100644
--- a/rust/kernel/devres.rs
+++ b/rust/kernel/devres.rs
@@ -326,15 +326,26 @@ fn register_foreign<P>(dev: &Device<Bound>, data: P) -> Result
 /// }
 ///
 /// fn from_bound_context(dev: &Device<Bound>) -> Result {
-///     devres::register(dev, Registration::new(), GFP_KERNEL)
+///     devres::register(dev, Registration::new(), GFP_KERNEL)?;
+///     Ok(())
 /// }
 /// ```
-pub fn register<T, E>(dev: &Device<Bound>, data: impl PinInit<T, E>, flags: Flags) -> Result
+pub fn register<'a, T, E>(
+    dev: &'a Device<Bound>,
+    data: impl PinInit<T, E>,
+    flags: Flags,
+) -> Result<&'a T>
 where
     T: Send + 'static,
     Error: From<E>,
 {
     let data = KBox::pin_init(data, flags)?;
 
+    let data_ptr = &raw const *data;
+
     register_foreign(dev, data)
+        // SAFETY: `dev` is valid for the lifetime of 'a. As long as there is a reference to
+        // `Device<Bound>`, it is guaranteed that the device is not unbound and data has not been
+        // dropped. Thus `data_ptr` is also valid for the lifetime of 'a.
+        .map(|()| unsafe { &*data_ptr })
 }
diff --git a/rust/kernel/drm/driver.rs b/rust/kernel/drm/driver.rs
index e09f977b5b51..51e0c7e30cc2 100644
--- a/rust/kernel/drm/driver.rs
+++ b/rust/kernel/drm/driver.rs
@@ -145,7 +145,8 @@ pub fn new_foreign_owned(
 
         let reg = Registration::<T>::new(drm, flags)?;
 
-        devres::register(dev, reg, GFP_KERNEL)
+        devres::register(dev, reg, GFP_KERNEL)?;
+        Ok(())
     }
 
     /// Returns a reference to the `Device` instance for this registration.

-- 
2.52.0

[PATCH v3 2/4] serdev: add rust private data to serdev_device

[Markus Probst]

Add rust private data to `struct serdev_device`, as it is required by the
rust abstraction added in the following commit
(rust: add basic serial device bus abstractions).

Signed-off-by: Markus Probst <markus.probst@posteo.de>
---
 include/linux/serdev.h | 15 +++++++++------
 1 file changed, 9 insertions(+), 6 deletions(-)

diff --git a/include/linux/serdev.h b/include/linux/serdev.h
index 5654c58eb73c..c74c345d60ae 100644
--- a/include/linux/serdev.h
+++ b/include/linux/serdev.h
@@ -33,12 +33,14 @@ struct serdev_device_ops {
 
 /**
  * struct serdev_device - Basic representation of an serdev device
- * @dev:	Driver model representation of the device.
- * @nr:		Device number on serdev bus.
- * @ctrl:	serdev controller managing this device.
- * @ops:	Device operations.
- * @write_comp	Completion used by serdev_device_write() internally
- * @write_lock	Lock to serialize access when writing data
+ * @dev:	       Driver model representation of the device.
+ * @nr:		       Device number on serdev bus.
+ * @ctrl:	       serdev controller managing this device.
+ * @ops:	       Device operations.
+ * @write_comp:	       Completion used by serdev_device_write() internally
+ * @write_lock:	       Lock to serialize access when writing data
+ * @rust_private_data: Private data for the rust abstraction. This should
+ *		       not be used by the C drivers.
  */
 struct serdev_device {
 	struct device dev;
@@ -47,6 +49,7 @@ struct serdev_device {
 	const struct serdev_device_ops *ops;
 	struct completion write_comp;
 	struct mutex write_lock;
+	void *rust_private_data;
 };
 
 static inline struct serdev_device *to_serdev_device(struct device *d)

-- 
2.52.0

[PATCH v3 3/4] 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>
---
 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           | 536 ++++++++++++++++++++++++++++++++++++++++
 6 files changed, 569 insertions(+)

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 083cc44aa952..ab521ba42673 100644
--- a/rust/bindings/bindings_helper.h
+++ b/rust/bindings/bindings_helper.h
@@ -80,6 +80,7 @@
 #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 a3c42e51f00a..9b87e9591cfd 100644
--- a/rust/helpers/helpers.c
+++ b/rust/helpers/helpers.c
@@ -53,6 +53,7 @@
 #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 3da92f18f4ee..90635f44e171 100644
--- a/rust/kernel/lib.rs
+++ b/rust/kernel/lib.rs
@@ -140,6 +140,8 @@
 pub mod scatterlist;
 pub mod security;
 pub mod seq_file;
+#[cfg(CONFIG_RUST_SERIAL_DEV_BUS_ABSTRACTIONS)]
+pub mod serdev;
 pub mod sizes;
 pub mod slice;
 #[cfg(CONFIG_SOC_BUS)]
diff --git a/rust/kernel/serdev.rs b/rust/kernel/serdev.rs
new file mode 100644
index 000000000000..d9fea4bd4439
--- /dev/null
+++ b/rust/kernel/serdev.rs
@@ -0,0 +1,536 @@
+// 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,
+    devres,
+    driver,
+    error::{
+        from_result,
+        to_result,
+        VTABLE_DEFAULT_ERROR, //
+    },
+    of,
+    prelude::*,
+    sync::Completion,
+    time::{
+        msecs_to_jiffies,
+        Jiffies,
+        Msecs, //
+    },
+    types::{
+        AlwaysRefCounted,
+        Opaque, //
+    }, //
+};
+
+use core::{
+    cell::UnsafeCell,
+    marker::PhantomData,
+    mem::offset_of,
+    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)`.
+// - `Drvdata<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 + 'static> driver::DriverLayout for Adapter<T> {
+    type DriverType = bindings::serdev_device_driver;
+    type DriverData = 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 + 'static> 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()) };
+    }
+}
+
+#[pin_data]
+struct PrivateData {
+    #[pin]
+    probe_complete: Completion,
+    error: UnsafeCell<bool>,
+}
+
+impl<T: Driver + 'static> 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 id_info = <Self as driver::Adapter>::id_info(sdev.as_ref());
+
+        from_result(|| {
+            let private_data = devres::register(
+                sdev.as_ref(),
+                try_pin_init!(PrivateData {
+                    probe_complete <- Completion::new(),
+                    error: false.into(),
+                }),
+                GFP_KERNEL,
+            )?;
+
+            // SAFETY: `sdev.as_raw()` is guaranteed to be a valid pointer to `serdev_device`.
+            unsafe {
+                (*sdev.as_raw()).rust_private_data =
+                    (&raw const *private_data).cast::<c_void>().cast_mut()
+            };
+
+            // 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::devm_serdev_device_open(sdev.as_ref().as_raw(), sdev.as_raw())
+            })?;
+
+            let data = T::probe(sdev, id_info);
+            let result = sdev.as_ref().set_drvdata(data);
+
+            // SAFETY: We have exclusive access to `private_data.error`.
+            unsafe { *private_data.error.get() = result.is_err() };
+
+            private_data.probe_complete.complete_all();
+
+            result.map(|()| 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<T>>`.
+        let data = unsafe { sdev.as_ref().drvdata_borrow::<T>() };
+
+        T::unbind(sdev, data);
+    }
+
+    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::CoreInternal>>() };
+
+        // SAFETY:
+        // - The serial device bus only ever calls the receive buf callback with a valid pointer to
+        //   a `struct serdev_device`.
+        // - `receive_buf_callback` is only ever called after a successful call to
+        //   `probe_callback`, hence it's guaranteed that `sdev.private_data` is a pointer
+        //   to a valid `PrivateData`.
+        let private_data = unsafe { &*(*sdev.as_raw()).rust_private_data.cast::<PrivateData>() };
+
+        private_data.probe_complete.wait_for_completion();
+
+        // SAFETY: No one has exclusive access to `private_data.error`.
+        if unsafe { *private_data.error.get() } {
+            return length;
+        }
+
+        // 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<T>>`.
+        let data = unsafe { sdev.as_ref().drvdata_borrow::<T>() };
+
+        // 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, buf)
+    }
+}
+
+impl<T: Driver + 'static> 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 = ();
+///     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(
+///         sdev: &serdev::Device<Core>,
+///         _id_info: Option<&Self::IdInfo>,
+///     ) -> impl PinInit<Self, Error> {
+///         sdev.set_baudrate(115200);
+///         sdev.write_all(b"Hello\n", serdev::Timeout::Max)?;
+///         Ok(MyDriver)
+///     }
+/// }
+///```
+#[vtable]
+pub trait Driver: Send {
+    /// 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 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(
+        sdev: &Device<device::Core>,
+        id_info: Option<&Self::IdInfo>,
+    ) -> impl PinInit<Self, Error>;
+
+    /// 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 `Self::drop`.
+    fn unbind(sdev: &Device<device::Core>, this: Pin<&Self>) {
+        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(sdev: &Device<device::Bound>, this: Pin<&Self>, 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> {
+        // 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> {
+        // 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 {}

-- 
2.52.0

[PATCH v3 4/4] 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>
---
 samples/rust/Kconfig               | 11 +++++
 samples/rust/Makefile              |  1 +
 samples/rust/rust_driver_serdev.rs | 86 ++++++++++++++++++++++++++++++++++++++
 3 files changed, 98 insertions(+)

diff --git a/samples/rust/Kconfig b/samples/rust/Kconfig
index c49ab9106345..a421470d2c52 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"
+	depends on SERIAL_DEV_BUS
+	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..8cf3fb451b22
--- /dev/null
+++ b/samples/rust/rust_driver_serdev.rs
@@ -0,0 +1,86 @@
+// 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 = ();
+    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(
+        sdev: &serdev::Device<Core>,
+        _info: Option<&Self::IdInfo>,
+    ) -> impl PinInit<Self, Error> {
+        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(sdev: &serdev::Device<Bound>, _this: Pin<&Self>, data: &[u8]) -> usize {
+        let _ = sdev.write_all(data, serdev::Timeout::Max);
+        data.len()
+    }
+}
+
+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",
+}

-- 
2.52.0

Re: [PATCH v3 2/4] serdev: add rust private data to serdev_device

[Greg Kroah-Hartman]

On Fri, Mar 13, 2026 at 06:12:31PM +0000, Markus Probst wrote:
> Add rust private data to `struct serdev_device`, as it is required by the
> rust abstraction added in the following commit
> (rust: add basic serial device bus abstractions).

why is rust "special" here?  What's wrong with the existing private
pointer in this structure?  Why must we add another one?

thanks,

greg k-h

Re: [PATCH v3 2/4] serdev: add rust private data to serdev_device

[Markus Probst]

[-- Attachment #1: Type: text/plain, Size: 1439 bytes --]

On Sat, 2026-03-14 at 09:07 +0100, Greg Kroah-Hartman wrote:
> On Fri, Mar 13, 2026 at 06:12:31PM +0000, Markus Probst wrote:
> > Add rust private data to `struct serdev_device`, as it is required by the
> > rust abstraction added in the following commit
> > (rust: add basic serial device bus abstractions).
> 
> why is rust "special" here?  What's wrong with the existing private
> pointer in this structure?  Why must we add another one?
Because in rust, the device drvdata will be set after probe has run. In
serdev, once the device has been opened, it can receive data. It must
be opened either inside probe or before probe, because it can only be
configured (baudrate, flow control etc.) and data written to after it
has been opened. Because it can receive data before drvdata has been
set yet, we need to ensure it waits on data receival for the probe to
be finished. Otherwise this would be a null pointer dereference. To do
this, we need to store a `Completion` for it to wait and a `bool` in
case the probe exits with an error. We cannot store this data in the
device drvdata, because this is where the drivers drvdata goes. We also
cannot create a wrapper of the drivers drvdata, because
`Device::drvdata::<T>()` would always fail in that case. That is why we
need a "rust_private_data" for this abstraction to store the
`Completion` and `bool`.

Thanks
- Markus Probst

> 
> thanks,
> 
> greg k-h

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Re: [PATCH v3 2/4] serdev: add rust private data to serdev_device

[Greg Kroah-Hartman]

On Sat, Mar 14, 2026 at 11:42:02AM +0000, Markus Probst wrote:
> On Sat, 2026-03-14 at 09:07 +0100, Greg Kroah-Hartman wrote:
> > On Fri, Mar 13, 2026 at 06:12:31PM +0000, Markus Probst wrote:
> > > Add rust private data to `struct serdev_device`, as it is required by the
> > > rust abstraction added in the following commit
> > > (rust: add basic serial device bus abstractions).
> > 
> > why is rust "special" here?  What's wrong with the existing private
> > pointer in this structure?  Why must we add another one?
> Because in rust, the device drvdata will be set after probe has run. In
> serdev, once the device has been opened, it can receive data. It must
> be opened either inside probe or before probe, because it can only be
> configured (baudrate, flow control etc.) and data written to after it
> has been opened. Because it can receive data before drvdata has been
> set yet, we need to ensure it waits on data receival for the probe to
> be finished. Otherwise this would be a null pointer dereference. To do
> this, we need to store a `Completion` for it to wait and a `bool` in
> case the probe exits with an error. We cannot store this data in the
> device drvdata, because this is where the drivers drvdata goes. We also
> cannot create a wrapper of the drivers drvdata, because
> `Device::drvdata::<T>()` would always fail in that case. That is why we
> need a "rust_private_data" for this abstraction to store the
> `Completion` and `bool`.

So why is this any different from any other bus type?  I don't see the
"uniqueness" here that has not required this to happen for PCI or USB or
anything else.

What am I missing?

Also, all of this information MUST be in the changelog text in order for
us to be able to accept it.  You need to say _why_ a change is needed,
not just _what_ the change does, as you know.

thanks,

greg k-h

Re: [PATCH v3 2/4] serdev: add rust private data to serdev_device

[Markus Probst]

[-- Attachment #1: Type: text/plain, Size: 2220 bytes --]

On Sat, 2026-03-14 at 12:52 +0100, Greg Kroah-Hartman wrote:
> On Sat, Mar 14, 2026 at 11:42:02AM +0000, Markus Probst wrote:
> > On Sat, 2026-03-14 at 09:07 +0100, Greg Kroah-Hartman wrote:
> > > On Fri, Mar 13, 2026 at 06:12:31PM +0000, Markus Probst wrote:
> > > > Add rust private data to `struct serdev_device`, as it is required by the
> > > > rust abstraction added in the following commit
> > > > (rust: add basic serial device bus abstractions).
> > > 
> > > why is rust "special" here?  What's wrong with the existing private
> > > pointer in this structure?  Why must we add another one?
> > Because in rust, the device drvdata will be set after probe has run. In
> > serdev, once the device has been opened, it can receive data. It must
> > be opened either inside probe or before probe, because it can only be
> > configured (baudrate, flow control etc.) and data written to after it
> > has been opened. Because it can receive data before drvdata has been
> > set yet, we need to ensure it waits on data receival for the probe to
> > be finished. Otherwise this would be a null pointer dereference. To do
> > this, we need to store a `Completion` for it to wait and a `bool` in
> > case the probe exits with an error. We cannot store this data in the
> > device drvdata, because this is where the drivers drvdata goes. We also
> > cannot create a wrapper of the drivers drvdata, because
> > `Device::drvdata::<T>()` would always fail in that case. That is why we
> > need a "rust_private_data" for this abstraction to store the
> > `Completion` and `bool`.
> 
> So why is this any different from any other bus type?  I don't see the
> "uniqueness" here that has not required this to happen for PCI or USB or
> anything else.
> 
> What am I missing?
In Short:
In serdev, we have to handle incoming device data (serdev calls on a
function pointer we provide in advance), even in the case that the
driver hasn't completed probe yet.

> 
> Also, all of this information MUST be in the changelog text in order for
> us to be able to accept it.  You need to say _why_ a change is needed,
> not just _what_ the change does, as you know.
Will do.

Thanks
- Markus Probst

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Re: [PATCH v3 2/4] serdev: add rust private data to serdev_device

[Alice Ryhl]

On Sat, Mar 14, 2026 at 12:08:09PM +0000, Markus Probst wrote:
> On Sat, 2026-03-14 at 12:52 +0100, Greg Kroah-Hartman wrote:
> > On Sat, Mar 14, 2026 at 11:42:02AM +0000, Markus Probst wrote:
> > > On Sat, 2026-03-14 at 09:07 +0100, Greg Kroah-Hartman wrote:
> > > > On Fri, Mar 13, 2026 at 06:12:31PM +0000, Markus Probst wrote:
> > > > > Add rust private data to `struct serdev_device`, as it is required by the
> > > > > rust abstraction added in the following commit
> > > > > (rust: add basic serial device bus abstractions).
> > > > 
> > > > why is rust "special" here?  What's wrong with the existing private
> > > > pointer in this structure?  Why must we add another one?
> > > Because in rust, the device drvdata will be set after probe has run. In
> > > serdev, once the device has been opened, it can receive data. It must
> > > be opened either inside probe or before probe, because it can only be
> > > configured (baudrate, flow control etc.) and data written to after it
> > > has been opened. Because it can receive data before drvdata has been
> > > set yet, we need to ensure it waits on data receival for the probe to
> > > be finished. Otherwise this would be a null pointer dereference. To do
> > > this, we need to store a `Completion` for it to wait and a `bool` in
> > > case the probe exits with an error. We cannot store this data in the
> > > device drvdata, because this is where the drivers drvdata goes. We also
> > > cannot create a wrapper of the drivers drvdata, because
> > > `Device::drvdata::<T>()` would always fail in that case. That is why we
> > > need a "rust_private_data" for this abstraction to store the
> > > `Completion` and `bool`.
> > 
> > So why is this any different from any other bus type?  I don't see the
> > "uniqueness" here that has not required this to happen for PCI or USB or
> > anything else.
> > 
> > What am I missing?
> In Short:
> In serdev, we have to handle incoming device data (serdev calls on a
> function pointer we provide in advance), even in the case that the
> driver hasn't completed probe yet.

Why can the function pointers be called during probe?

Alice

Re: [PATCH v3 2/4] serdev: add rust private data to serdev_device

[Greg Kroah-Hartman]

On Sat, Mar 14, 2026 at 12:08:09PM +0000, Markus Probst wrote:
> On Sat, 2026-03-14 at 12:52 +0100, Greg Kroah-Hartman wrote:
> > On Sat, Mar 14, 2026 at 11:42:02AM +0000, Markus Probst wrote:
> > > On Sat, 2026-03-14 at 09:07 +0100, Greg Kroah-Hartman wrote:
> > > > On Fri, Mar 13, 2026 at 06:12:31PM +0000, Markus Probst wrote:
> > > > > Add rust private data to `struct serdev_device`, as it is required by the
> > > > > rust abstraction added in the following commit
> > > > > (rust: add basic serial device bus abstractions).
> > > > 
> > > > why is rust "special" here?  What's wrong with the existing private
> > > > pointer in this structure?  Why must we add another one?
> > > Because in rust, the device drvdata will be set after probe has run. In
> > > serdev, once the device has been opened, it can receive data. It must
> > > be opened either inside probe or before probe, because it can only be
> > > configured (baudrate, flow control etc.) and data written to after it
> > > has been opened. Because it can receive data before drvdata has been
> > > set yet, we need to ensure it waits on data receival for the probe to
> > > be finished. Otherwise this would be a null pointer dereference. To do
> > > this, we need to store a `Completion` for it to wait and a `bool` in
> > > case the probe exits with an error. We cannot store this data in the
> > > device drvdata, because this is where the drivers drvdata goes. We also
> > > cannot create a wrapper of the drivers drvdata, because
> > > `Device::drvdata::<T>()` would always fail in that case. That is why we
> > > need a "rust_private_data" for this abstraction to store the
> > > `Completion` and `bool`.
> > 
> > So why is this any different from any other bus type?  I don't see the
> > "uniqueness" here that has not required this to happen for PCI or USB or
> > anything else.
> > 
> > What am I missing?
> In Short:
> In serdev, we have to handle incoming device data (serdev calls on a
> function pointer we provide in advance), even in the case that the
> driver hasn't completed probe yet.

But how is that any different from a USB or PCI driver doing the same
thing?  Why is serdev so unique here?  What specific serdev function
causes this and why isn't it an issue with the C api?  Can we change the
C code to not require this?

thanks,

greg k-h

Re: [PATCH v3 2/4] serdev: add rust private data to serdev_device

[Danilo Krummrich]

On Sat Mar 14, 2026 at 2:31 PM CET, Greg Kroah-Hartman wrote:
> On Sat, Mar 14, 2026 at 12:08:09PM +0000, Markus Probst wrote:
>> On Sat, 2026-03-14 at 12:52 +0100, Greg Kroah-Hartman wrote:
>> > On Sat, Mar 14, 2026 at 11:42:02AM +0000, Markus Probst wrote:
>> > > On Sat, 2026-03-14 at 09:07 +0100, Greg Kroah-Hartman wrote:
>> > > > On Fri, Mar 13, 2026 at 06:12:31PM +0000, Markus Probst wrote:
>> > > > > Add rust private data to `struct serdev_device`, as it is required by the
>> > > > > rust abstraction added in the following commit
>> > > > > (rust: add basic serial device bus abstractions).
>> > > > 
>> > > > why is rust "special" here?  What's wrong with the existing private
>> > > > pointer in this structure?  Why must we add another one?
>> > > Because in rust, the device drvdata will be set after probe has run. In
>> > > serdev, once the device has been opened, it can receive data. It must
>> > > be opened either inside probe or before probe, because it can only be
>> > > configured (baudrate, flow control etc.) and data written to after it
>> > > has been opened. Because it can receive data before drvdata has been
>> > > set yet, we need to ensure it waits on data receival for the probe to
>> > > be finished. Otherwise this would be a null pointer dereference. To do
>> > > this, we need to store a `Completion` for it to wait and a `bool` in
>> > > case the probe exits with an error. We cannot store this data in the
>> > > device drvdata, because this is where the drivers drvdata goes. We also
>> > > cannot create a wrapper of the drivers drvdata, because
>> > > `Device::drvdata::<T>()` would always fail in that case. That is why we
>> > > need a "rust_private_data" for this abstraction to store the
>> > > `Completion` and `bool`.
>> > 
>> > So why is this any different from any other bus type?  I don't see the
>> > "uniqueness" here that has not required this to happen for PCI or USB or
>> > anything else.
>> > 
>> > What am I missing?
>> In Short:
>> In serdev, we have to handle incoming device data (serdev calls on a
>> function pointer we provide in advance), even in the case that the
>> driver hasn't completed probe yet.
>
> But how is that any different from a USB or PCI driver doing the same
> thing?  Why is serdev so unique here?  What specific serdev function
> causes this and why isn't it an issue with the C api?  Can we change the
> C code to not require this?

I think the idea is to avoid bugs as in the mhz19b driver [1].

This driver's probe() looks like this:


	serdev_device_set_client_ops(serdev, &mhz19b_ops);
	ret = devm_serdev_device_open(dev, serdev);

	// Lots of other initialization.

	serdev_device_set_drvdata(serdev, indio_dev);

But the receive_buf() callback from mhz19b_ops dereferences the driver's private
data.

Now, maybe this is actually prevented to become an actual race, since some
regulator is only enabled subsequently:

	devm_regulator_get_enable(dev, "vin");

But in any case in Rust it would be unsound as with this a driver could easily
cause undefined behavior with safe APIs.

Maybe it is as simple as letting the abstraction call serdev_device_open() only
after the driver's probe() has completed, but maybe there are reasons why that
is not an option, that's a serdev question.

[1] https://elixir.bootlin.com/linux/v6.19.7/source/drivers/iio/chemical/mhz19b.c#L260

Re: [PATCH v3 2/4] serdev: add rust private data to serdev_device

[Markus Probst]

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On Sat, 2026-03-14 at 14:42 +0100, Danilo Krummrich wrote:
> On Sat Mar 14, 2026 at 2:31 PM CET, Greg Kroah-Hartman wrote:
> > On Sat, Mar 14, 2026 at 12:08:09PM +0000, Markus Probst wrote:
> > > On Sat, 2026-03-14 at 12:52 +0100, Greg Kroah-Hartman wrote:
> > > > On Sat, Mar 14, 2026 at 11:42:02AM +0000, Markus Probst wrote:
> > > > > On Sat, 2026-03-14 at 09:07 +0100, Greg Kroah-Hartman wrote:
> > > > > > On Fri, Mar 13, 2026 at 06:12:31PM +0000, Markus Probst wrote:
> > > > > > > Add rust private data to `struct serdev_device`, as it is required by the
> > > > > > > rust abstraction added in the following commit
> > > > > > > (rust: add basic serial device bus abstractions).
> > > > > > 
> > > > > > why is rust "special" here?  What's wrong with the existing private
> > > > > > pointer in this structure?  Why must we add another one?
> > > > > Because in rust, the device drvdata will be set after probe has run. In
> > > > > serdev, once the device has been opened, it can receive data. It must
> > > > > be opened either inside probe or before probe, because it can only be
> > > > > configured (baudrate, flow control etc.) and data written to after it
> > > > > has been opened. Because it can receive data before drvdata has been
> > > > > set yet, we need to ensure it waits on data receival for the probe to
> > > > > be finished. Otherwise this would be a null pointer dereference. To do
> > > > > this, we need to store a `Completion` for it to wait and a `bool` in
> > > > > case the probe exits with an error. We cannot store this data in the
> > > > > device drvdata, because this is where the drivers drvdata goes. We also
> > > > > cannot create a wrapper of the drivers drvdata, because
> > > > > `Device::drvdata::<T>()` would always fail in that case. That is why we
> > > > > need a "rust_private_data" for this abstraction to store the
> > > > > `Completion` and `bool`.
> > > > 
> > > > So why is this any different from any other bus type?  I don't see the
> > > > "uniqueness" here that has not required this to happen for PCI or USB or
> > > > anything else.
> > > > 
> > > > What am I missing?
> > > In Short:
> > > In serdev, we have to handle incoming device data (serdev calls on a
> > > function pointer we provide in advance), even in the case that the
> > > driver hasn't completed probe yet.
> > 
> > But how is that any different from a USB or PCI driver doing the same
> > thing?  Why is serdev so unique here?  What specific serdev function
> > causes this and why isn't it an issue with the C api?  Can we change the
> > C code to not require this?
> 
> I think the idea is to avoid bugs as in the mhz19b driver [1].
> 
> This driver's probe() looks like this:
> 
> 
> 	serdev_device_set_client_ops(serdev, &mhz19b_ops);
> 	ret = devm_serdev_device_open(dev, serdev);
> 
> 	// Lots of other initialization.
> 
> 	serdev_device_set_drvdata(serdev, indio_dev);
> 
> But the receive_buf() callback from mhz19b_ops dereferences the driver's private
> data.
> 
> Now, maybe this is actually prevented to become an actual race, since some
> regulator is only enabled subsequently:
> 
> 	devm_regulator_get_enable(dev, "vin");
> 
> But in any case in Rust it would be unsound as with this a driver could easily
> cause undefined behavior with safe APIs.
> 
> Maybe it is as simple as letting the abstraction call serdev_device_open() only
> after the driver's probe() has completed, but maybe there are reasons why that
> is not an option, that's a serdev question.
If we call it after probe, calls to `serdev_device_set_baudrate`,
`serdev_device_set_flow_control`, `serdev_device_set_parity`,
`serdev_device_write_buf`, `serdev_device_write`,
`serdev_device_write_flush`, which are exposed via the rust abstraction
would result in a null pointer dereference.

Thanks
- Markus Probst

> 
> [1] https://elixir.bootlin.com/linux/v6.19.7/source/drivers/iio/chemical/mhz19b.c#L260

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Re: [PATCH v3 2/4] serdev: add rust private data to serdev_device

[Danilo Krummrich]

On Sat Mar 14, 2026 at 2:49 PM CET, Markus Probst wrote:
> On Sat, 2026-03-14 at 14:42 +0100, Danilo Krummrich wrote:
>> On Sat Mar 14, 2026 at 2:31 PM CET, Greg Kroah-Hartman wrote:
>> > On Sat, Mar 14, 2026 at 12:08:09PM +0000, Markus Probst wrote:
>> > > On Sat, 2026-03-14 at 12:52 +0100, Greg Kroah-Hartman wrote:
>> > > > On Sat, Mar 14, 2026 at 11:42:02AM +0000, Markus Probst wrote:
>> > > > > On Sat, 2026-03-14 at 09:07 +0100, Greg Kroah-Hartman wrote:
>> > > > > > On Fri, Mar 13, 2026 at 06:12:31PM +0000, Markus Probst wrote:
>> > > > > > > Add rust private data to `struct serdev_device`, as it is required by the
>> > > > > > > rust abstraction added in the following commit
>> > > > > > > (rust: add basic serial device bus abstractions).
>> > > > > > 
>> > > > > > why is rust "special" here?  What's wrong with the existing private
>> > > > > > pointer in this structure?  Why must we add another one?
>> > > > > Because in rust, the device drvdata will be set after probe has run. In
>> > > > > serdev, once the device has been opened, it can receive data. It must
>> > > > > be opened either inside probe or before probe, because it can only be
>> > > > > configured (baudrate, flow control etc.) and data written to after it
>> > > > > has been opened. Because it can receive data before drvdata has been
>> > > > > set yet, we need to ensure it waits on data receival for the probe to
>> > > > > be finished. Otherwise this would be a null pointer dereference. To do
>> > > > > this, we need to store a `Completion` for it to wait and a `bool` in
>> > > > > case the probe exits with an error. We cannot store this data in the
>> > > > > device drvdata, because this is where the drivers drvdata goes. We also
>> > > > > cannot create a wrapper of the drivers drvdata, because
>> > > > > `Device::drvdata::<T>()` would always fail in that case. That is why we
>> > > > > need a "rust_private_data" for this abstraction to store the
>> > > > > `Completion` and `bool`.
>> > > > 
>> > > > So why is this any different from any other bus type?  I don't see the
>> > > > "uniqueness" here that has not required this to happen for PCI or USB or
>> > > > anything else.
>> > > > 
>> > > > What am I missing?
>> > > In Short:
>> > > In serdev, we have to handle incoming device data (serdev calls on a
>> > > function pointer we provide in advance), even in the case that the
>> > > driver hasn't completed probe yet.
>> > 
>> > But how is that any different from a USB or PCI driver doing the same
>> > thing?  Why is serdev so unique here?  What specific serdev function
>> > causes this and why isn't it an issue with the C api?  Can we change the
>> > C code to not require this?
>> 
>> I think the idea is to avoid bugs as in the mhz19b driver [1].
>> 
>> This driver's probe() looks like this:
>> 
>> 
>> 	serdev_device_set_client_ops(serdev, &mhz19b_ops);
>> 	ret = devm_serdev_device_open(dev, serdev);
>> 
>> 	// Lots of other initialization.
>> 
>> 	serdev_device_set_drvdata(serdev, indio_dev);
>> 
>> But the receive_buf() callback from mhz19b_ops dereferences the driver's private
>> data.
>> 
>> Now, maybe this is actually prevented to become an actual race, since some
>> regulator is only enabled subsequently:
>> 
>> 	devm_regulator_get_enable(dev, "vin");
>> 
>> But in any case in Rust it would be unsound as with this a driver could easily
>> cause undefined behavior with safe APIs.
>> 
>> Maybe it is as simple as letting the abstraction call serdev_device_open() only
>> after the driver's probe() has completed, but maybe there are reasons why that
>> is not an option, that's a serdev question.
> If we call it after probe, calls to `serdev_device_set_baudrate`,
> `serdev_device_set_flow_control`, `serdev_device_set_parity`,
> `serdev_device_write_buf`, `serdev_device_write`,
> `serdev_device_write_flush`, which are exposed via the rust abstraction
> would result in a null pointer dereference.

Then maybe ensure that the driver's receive_buf() callback can only ever be
called after probe() has been completed? E.g. receive_buf() could be optional
and swapped out later on.

Re: [PATCH v3 2/4] serdev: add rust private data to serdev_device

[Markus Probst]

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On Sat, 2026-03-14 at 14:54 +0100, Danilo Krummrich wrote:
> On Sat Mar 14, 2026 at 2:49 PM CET, Markus Probst wrote:
> > On Sat, 2026-03-14 at 14:42 +0100, Danilo Krummrich wrote:
> > > On Sat Mar 14, 2026 at 2:31 PM CET, Greg Kroah-Hartman wrote:
> > > > On Sat, Mar 14, 2026 at 12:08:09PM +0000, Markus Probst wrote:
> > > > > On Sat, 2026-03-14 at 12:52 +0100, Greg Kroah-Hartman wrote:
> > > > > > On Sat, Mar 14, 2026 at 11:42:02AM +0000, Markus Probst wrote:
> > > > > > > On Sat, 2026-03-14 at 09:07 +0100, Greg Kroah-Hartman wrote:
> > > > > > > > On Fri, Mar 13, 2026 at 06:12:31PM +0000, Markus Probst wrote:
> > > > > > > > > Add rust private data to `struct serdev_device`, as it is required by the
> > > > > > > > > rust abstraction added in the following commit
> > > > > > > > > (rust: add basic serial device bus abstractions).
> > > > > > > > 
> > > > > > > > why is rust "special" here?  What's wrong with the existing private
> > > > > > > > pointer in this structure?  Why must we add another one?
> > > > > > > Because in rust, the device drvdata will be set after probe has run. In
> > > > > > > serdev, once the device has been opened, it can receive data. It must
> > > > > > > be opened either inside probe or before probe, because it can only be
> > > > > > > configured (baudrate, flow control etc.) and data written to after it
> > > > > > > has been opened. Because it can receive data before drvdata has been
> > > > > > > set yet, we need to ensure it waits on data receival for the probe to
> > > > > > > be finished. Otherwise this would be a null pointer dereference. To do
> > > > > > > this, we need to store a `Completion` for it to wait and a `bool` in
> > > > > > > case the probe exits with an error. We cannot store this data in the
> > > > > > > device drvdata, because this is where the drivers drvdata goes. We also
> > > > > > > cannot create a wrapper of the drivers drvdata, because
> > > > > > > `Device::drvdata::<T>()` would always fail in that case. That is why we
> > > > > > > need a "rust_private_data" for this abstraction to store the
> > > > > > > `Completion` and `bool`.
> > > > > > 
> > > > > > So why is this any different from any other bus type?  I don't see the
> > > > > > "uniqueness" here that has not required this to happen for PCI or USB or
> > > > > > anything else.
> > > > > > 
> > > > > > What am I missing?
> > > > > In Short:
> > > > > In serdev, we have to handle incoming device data (serdev calls on a
> > > > > function pointer we provide in advance), even in the case that the
> > > > > driver hasn't completed probe yet.
> > > > 
> > > > But how is that any different from a USB or PCI driver doing the same
> > > > thing?  Why is serdev so unique here?  What specific serdev function
> > > > causes this and why isn't it an issue with the C api?  Can we change the
> > > > C code to not require this?
> > > 
> > > I think the idea is to avoid bugs as in the mhz19b driver [1].
> > > 
> > > This driver's probe() looks like this:
> > > 
> > > 
> > > 	serdev_device_set_client_ops(serdev, &mhz19b_ops);
> > > 	ret = devm_serdev_device_open(dev, serdev);
> > > 
> > > 	// Lots of other initialization.
> > > 
> > > 	serdev_device_set_drvdata(serdev, indio_dev);
> > > 
> > > But the receive_buf() callback from mhz19b_ops dereferences the driver's private
> > > data.
> > > 
> > > Now, maybe this is actually prevented to become an actual race, since some
> > > regulator is only enabled subsequently:
> > > 
> > > 	devm_regulator_get_enable(dev, "vin");
> > > 
> > > But in any case in Rust it would be unsound as with this a driver could easily
> > > cause undefined behavior with safe APIs.
> > > 
> > > Maybe it is as simple as letting the abstraction call serdev_device_open() only
> > > after the driver's probe() has completed, but maybe there are reasons why that
> > > is not an option, that's a serdev question.
> > If we call it after probe, calls to `serdev_device_set_baudrate`,
> > `serdev_device_set_flow_control`, `serdev_device_set_parity`,
> > `serdev_device_write_buf`, `serdev_device_write`,
> > `serdev_device_write_flush`, which are exposed via the rust abstraction
> > would result in a null pointer dereference.
> 
> Then maybe ensure that the driver's receive_buf() callback can only ever be
> called after probe() has been completed? E.g. receive_buf() could be optional
> and swapped out later on.
I am not exactly sure what you mean by "could be optional and swapped
out later on".

Also,
the function pointer cannot be changed while the device is open, as
this could introduce a race condition. In addition if it was prior set
to NULL and data was received, this data would be lost.

Thanks
- Markus Probst


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Claude review: rust: add basic serial device bus abstractions

[Claude Code Review Bot]

Overall Series Review

Subject: rust: add basic serial device bus abstractions
Author: Markus Probst <markus.probst@posteo.de>
Patches: 15
Reviewed: 2026-03-16T12:17:34.917979

---

This is a v3 patch series adding Rust abstractions for the Linux serial device bus (serdev) subsystem, consisting of 4 patches: a devres API change, a C-side struct modification, the main Rust abstraction, and a sample driver.

The overall design follows established kernel Rust driver patterns (similar to platform, USB, auxiliary bus abstractions) and the code is well-structured. However, there are several concerns, ranging from a **critical safety issue** in the `devres::register` lifetime change, to race condition concerns in the probe/receive synchronization, and a few minor API design questions.

---
Generated by Claude Code Patch Reviewer

Claude review: rust: devres: return reference in `devres::register`

[Claude Code Review Bot]

Patch Review

This patch changes `devres::register` to return `Result<&'a T>` instead of `Result`, tying the returned reference's lifetime to the `Device<Bound>` reference.

**Critical safety concern with the lifetime reasoning:**

```rust
+pub fn register<'a, T, E>(
+    dev: &'a Device<Bound>,
+    data: impl PinInit<T, E>,
+    flags: Flags,
+) -> Result<&'a T>
```

The SAFETY comment states:

```rust
+        // SAFETY: `dev` is valid for the lifetime of 'a. As long as there is a reference to
+        // `Device<Bound>`, it is guaranteed that the device is not unbound and data has not been
+        // dropped. Thus `data_ptr` is also valid for the lifetime of 'a.
```

The issue is that `data` is moved into `register_foreign` via `KBox::pin_init` and then consumed by `into_foreign()` inside `register_foreign`. The raw pointer `data_ptr` is taken *before* the data is registered with devres. If `register_foreign` fails (returns an error), `data` is dropped, but we never reach the `.map()` so that's OK. However, the lifetime argument is subtle: the devres-managed data could in theory be freed by devres callbacks (e.g., if the device is removed concurrently) while a `&'a T` reference is still held. The safety argument relies on `Device<Bound>` guaranteeing the device won't unbind while the reference exists. This needs careful scrutiny from the Rust-for-Linux maintainers (Danilo, Benno, Alice) to verify the invariant actually holds.

**The callers now discard the return value:**

```rust
-        devres::register(dev, Self::new()?, GFP_KERNEL)
+        devres::register(dev, Self::new()?, GFP_KERNEL)?;
+        Ok(())
```

This works but changes the API for all existing callers to require `?;` + `Ok(())` where they previously just returned the `Result`. This is somewhat unfortunate ergonomically. An alternative approach might be a separate `devres::register_ref` function to avoid forcing this pattern on callers that don't need the reference.

---
Generated by Claude Code Patch Reviewer

Claude review: Re: [PATCH v3 2/4] serdev: add rust private data to serdev_device

[Claude Code Review Bot]

Patch Review

```c
+	void *rust_private_data;
```

Adding a `void *` field to `struct serdev_device` purely for Rust abstraction use is somewhat controversial. This adds overhead to every `serdev_device` in the system, even when Rust is not used. 

**Concern:** Why not use the existing `dev_set_drvdata`/`dev_get_drvdata` mechanism for this? The patch series uses `dev_set_drvdata` for the driver's own data (`T`) and then needs this extra field for `PrivateData` (the completion/error pair). This suggests the abstraction design could be reworked to avoid needing two separate private data fields — for example, by wrapping the driver data and the completion together into a single struct stored via `dev_set_drvdata`.

The kdoc alignment changes are good cleanup (adding missing colons on `@write_comp:` and `@write_lock:`).

**Initialization concern:** The new `rust_private_data` field is never explicitly initialized in the C code that allocates `serdev_device`. It will be zero-initialized if the struct is allocated with `kzalloc`, but this should be documented or verified.

---
Generated by Claude Code Patch Reviewer

Claude review: rust: add basic serial device bus abstractions

[Claude Code Review Bot]

Patch Review

This is the main patch. Several observations:

**1. Timeout::Max maps to 0, which is wrong:**

```rust
+impl Timeout {
+    fn into_jiffies(self) -> isize {
+        match self {
+            ...
+            Self::Max => 0,
+        }
+    }
+}
```

`MAX_SCHEDULE_TIMEOUT` is `LONG_MAX` (i.e., `c_long::MAX`), not 0. A timeout of 0 means "don't wait at all" in `serdev_device_write()`. The `Timeout::Max` variant's doc says "Wait as long as possible" and references `MAX_SCHEDULE_TIMEOUT`, but then passes 0, which is the exact opposite. This should be:

```rust
Self::Max => isize::MAX, // or kernel::task::MAX_SCHEDULE_TIMEOUT
```

**2. Race condition in probe/receive synchronization:**

The `PrivateData` struct uses a `Completion` to synchronize `receive_buf_callback` with probe completion:

```rust
+        private_data.probe_complete.wait_for_completion();
+
+        // SAFETY: No one has exclusive access to `private_data.error`.
+        if unsafe { *private_data.error.get() } {
+            return length;
+        }
```

The `error` field uses `UnsafeCell<bool>` without any synchronization primitive. The SAFETY comment "No one has exclusive access to `private_data.error`" doesn't actually justify the safety — it's the *opposite* of what you'd want. The concern is whether the write to `error` in probe is guaranteed to be visible in `receive_buf_callback` on another thread. The `Completion` itself should provide a memory barrier (via `complete_all`/`wait_for_completion`), so the ordering is likely correct in practice, but this should be documented explicitly. Using an `AtomicBool` would be cleaner and avoid the need for `unsafe` altogether.

**3. `set_baudrate` returns `Result<(), u32>` instead of idiomatic kernel `Result`:**

```rust
+    pub fn set_baudrate(&self, speed: u32) -> Result<(), u32> {
```

Returning the actual baudrate set on failure is useful information, but the `Result<(), u32>` type is non-standard for kernel Rust code. The C function `serdev_device_set_baudrate` returns the actual speed set (which may differ from requested). The sample driver checks `is_err()` and returns `EINVAL`, losing the actual value. Consider either returning `Result<u32>` (the actual speed set) or `Result` with a standard error code.

**4. `write` returns `Result<u32>` but `write_all` returns `Result<usize>` — inconsistent types:**

```rust
+    pub fn write_all(&self, data: &[u8], timeout: Timeout) -> Result<usize> {
...
+    pub fn write(&self, data: &[u8]) -> Result<u32> {
```

Both should consistently use `usize` for byte counts.

**5. The `write` function wraps `serdev_device_write_buf` which returns `ssize_t`:**

```rust
+        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())
```

Casting `ssize_t` (which is `isize`/`i64` on 64-bit) to `i32` could truncate positive values. Since this returns the number of bytes written, if `data.len()` > `i32::MAX`, the cast would produce an incorrect error. The same issue exists in `write_all`. Use `ret as i32` carefully — `to_result` expects a C `int`, but the value range should be OK in practice since write buffers won't exceed `i32::MAX`.

**6. `set_baudrate`, `set_flow_control`, `set_parity`, `write`, `write_all`, `write_flush`, `wait_until_sent` are all on `Device<Bound>`, but probe receives `Device<Core>`:**

Looking at the sample driver, `sdev.set_baudrate(...)` is called in `probe` which receives `&Device<Core>`. This compiles because of `impl_device_context_deref` which lets `Device<Core>` deref to `Device<Bound>`. This is the standard pattern, so it's fine.

**7. Typo in doc comments:**

```rust
+    /// Even partiy.
```

Should be "parity".

```rust
+    /// [ Device::wait_until_sent`]
```

Missing `[` — should be `[`Device::wait_until_sent`]`. This appears twice.

**8. The `Kconfig` entry `RUST_SERIAL_DEV_BUS_ABSTRACTIONS` should probably be inside the `if SERIAL_DEV_BUS` block:**

```diff
+config RUST_SERIAL_DEV_BUS_ABSTRACTIONS
+	bool "Rust Serial device bus abstractions"
+	depends on RUST
+	select SERIAL_DEV_BUS
```

It uses `select SERIAL_DEV_BUS` rather than `depends on`, which means enabling the Rust abstractions will force-enable `SERIAL_DEV_BUS`. This is placed *before* `if SERIAL_DEV_BUS`, which is a bit odd. Consider using `depends on SERIAL_DEV_BUS` instead.

**9. `remove_callback` doesn't call `drvdata_obtain` to free the driver data:**

```rust
+    extern "C" fn remove_callback(sdev: *mut bindings::serdev_device) {
+        let sdev = unsafe { &*sdev.cast::<Device<device::CoreInternal>>() };
+        let data = unsafe { sdev.as_ref().drvdata_borrow::<T>() };
+        T::unbind(sdev, data);
+    }
```

It borrows but never takes ownership of the drvdata. The data appears to be freed by devres when the device is released, since `set_drvdata` stores it via `dev_set_drvdata`. But wait — `set_drvdata` stores data via `into_foreign()` and there's no corresponding `from_foreign()` call. The data should be cleaned up by the devres system if `set_drvdata` registers a devres action, but looking at the `device.rs` code, `set_drvdata` does *not* register a devres — it just calls `dev_set_drvdata`. This looks like a **memory leak** — the `Pin<KBox<T>>` stored via `set_drvdata` is never freed. Other bus drivers (platform, etc.) likely call `drvdata_obtain` in their remove callbacks. This needs to be verified.

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Claude review: samples: rust: add Rust serial device bus sample device driver

[Claude Code Review Bot]

Patch Review

The sample is clean and demonstrates the API well.

**Missing dependency in Kconfig:**

```
+config SAMPLE_RUST_DRIVER_SERDEV
+	tristate "Serial Device Bus Device Driver"
+	depends on SERIAL_DEV_BUS
```

This should also `depends on RUST_SERIAL_DEV_BUS_ABSTRACTIONS` (or `select` it), since the sample uses `kernel::serdev` which is gated behind that config option.

**The sample stores an `ARef<serdev::Device>` but never uses it functionally:**

```rust
+struct SampleDriver {
+    sdev: ARef<serdev::Device>,
+}
```

It's only used in `Drop` for a debug message. This is fine for a sample, but the reference counting should be correct — `sdev.into()` in `probe` calls `impl_device_context_into_aref` which should increment the refcount.

**Minor: `"GPL v2"` vs `"GPL"`:**

```rust
+    license: "GPL v2",
```

Modern kernel modules typically use just `"GPL"`. `"GPL v2"` is also accepted but `"GPL"` is the recommended form.

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Generated by Claude Code Patch Reviewer