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

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 abstraction well. A few notes:

**`set_baudrate` error handling is odd due to the API design:**

```rust
if sdev
    .set_baudrate(
        dev.fwnode()
            .and_then(|fwnode| fwnode.property_read(c"baudrate").optional())
            .unwrap_or(115200),
    )
    .is_err()
{
    return Err(EINVAL);
}
```

This discards the actual baudrate returned in the error. If `set_baudrate` returned `u32` instead of `Result<(), u32>`, this would be simpler and more informative.

**Echo server with `Timeout::Max` would hang:** Due to the `Timeout::Max` bug (returning 0), `write_all` in receive would return immediately or with ETIMEDOUT rather than actually waiting. This makes the sample non-functional in practice.

**The sample stores an `ARef<serdev::Device>` but never uses it** (except in Drop for a debug message). This is fine for a sample but worth noting.

---
Generated by Claude Code Patch Reviewer

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.

---
Generated by Claude Code Patch Reviewer

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

[Claude Code Review Bot]

Patch Review

A clean sample that demonstrates probe, receive (echo/loopback), and cleanup. A few observations:

**Error in receive is swallowed**:

```rust
+    fn receive(sdev: &serdev::Device<Bound>, _this: Pin<&Self>, data: &[u8]) -> usize {
+        let _ = sdev.write_all(data, serdev::Timeout::Max);
+        data.len()
+    }
```

The `write_all` error is discarded with `let _ = ...`. For a sample this is acceptable, but a comment like `// Ignore write errors for simplicity` would be helpful.

**Strict baudrate matching**:

```rust
+        if sdev
+            .set_baudrate(...)
+            .is_err()
+        {
+            return Err(EINVAL);
+        }
```

This fails probe if the exact baudrate isn't matched. As noted above, many serial controllers approximate the baudrate. For a sample this is fine, but it could be confusing if someone tries to run this on real hardware.

**License string**: `"GPL v2"` is used, which is the correct form for `MODULE_LICENSE`.

**Overall the sample is clean and well-structured**, demonstrating the key abstractions (OF/ACPI ID tables, probe, receive, device reference management via `ARef`, Drop-based cleanup).

---
Generated by Claude Code Patch Reviewer

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

[Claude Code Review Bot]

Patch Review

Clean and functional sample driver. A few observations:

**Echoing data in receive callback:**
```rust
+    fn receive(sdev: &serdev::Device<Bound>, _this: Pin<&Self>, data: &[u8]) -> usize {
+        let _ = sdev.write_all(data, serdev::Timeout::Max);
+        data.len()
+    }
```
The `write_all` with `Timeout::Max` could block indefinitely if the device can't accept data. For a sample this is acceptable, but a brief comment noting this is intentional would be helpful. Also, `let _ =` silently discards write errors, which is fine for a sample.

**Baudrate handling:**
```rust
+        if sdev
+            .set_baudrate(
+                dev.fwnode()
+                    .and_then(|fwnode| fwnode.property_read(c"baudrate").optional())
+                    .unwrap_or(115200),
+            )
+            .is_err()
+        {
+            return Err(EINVAL);
+        }
```
Reading a `baudrate` property from firmware and falling back to 115200 is a reasonable pattern. The `set_baudrate` error (which contains the actual baudrate set) is discarded and replaced with `EINVAL`, which is appropriate.

**Kconfig entry properly uses `select`:**
```
+	select RUST_SERIAL_DEV_BUS_ABSTRACTIONS
```
This ensures the abstraction is compiled when the sample is enabled. Correct.

The sample effectively demonstrates OF and ACPI device table setup, probe/remove lifecycle, baudrate/flow-control/parity configuration, and the receive callback -- good coverage for a sample driver.

---
Generated by Claude Code Patch Reviewer

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 key API surface well.

**One issue with the sample probe:**
```rust
fn probe(
    sdev: &serdev::Device<Core>,
    _info: Option<&Self::IdInfo>,
) -> impl PinInit<Self, Error> {
    ...
    if sdev.set_baudrate(...).is_err() {
        return Err(EINVAL);
    }
```
The `set_baudrate` method is on `Device<Bound>`, but `sdev` is `&Device<Core>`. This works via the deref coercion chain, which is correct but could be surprising to readers. A brief comment in the abstraction's module-level docs explaining the device context hierarchy and auto-deref would help (though this is a broader Rust-for-Linux documentation issue, not specific to this patch).

**The receive callback echoes data back:**
```rust
fn receive(sdev: &serdev::Device<Bound>, _this: Pin<&Self>, data: &[u8]) -> usize {
    let _ = sdev.write_all(data, serdev::Timeout::Max);
    data.len()
}
```
This is fine for a sample. The `let _ =` discards the write result, which is acceptable for demonstration purposes. Note that this always returns `data.len()` (claiming all data was consumed) regardless of whether `write_all` succeeded, which is the right behavior for a simple echo.

**The `SampleDriver` stores an `ARef<serdev::Device>` but only uses it in `Drop`** for a debug message. This is fine as a sample demonstrating how to keep a reference to the device.

No blocking issues with this patch.

---
Generated by Claude Code Patch Reviewer

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

[Claude Code Review Bot]

Patch Review

Clean, well-structured sample driver. It demonstrates:
- OF and ACPI device table registration
- Probe with optional baudrate property from firmware
- Receive callback that echoes data back
- Drop for cleanup logging

```rust
+    fn receive(sdev: &serdev::Device<Bound>, _this: Pin<&Self>, data: &[u8]) -> usize {
+        let _ = sdev.write_all(data, serdev::Timeout::Max);
+        data.len()
+    }
```

The `let _ =` silently discards write errors during echo, which is fine for a sample. The function always returns `data.len()` claiming all bytes were consumed regardless of write success — acceptable for a demo.

**Minor:** The Kconfig entry doesn't have a `depends on SAMPLES` guard, but that's consistent with other sample drivers in the same file.

No significant issues with this patch.

---
Generated by Claude Code Patch Reviewer

[PATCH v12 0/3] rust: add basic serial device bus abstractions

[Markus Probst via B4 Relay]

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] and [2].

[1]
https://lore.kernel.org/rust-for-linux/20260525202921.124698-1-dakr@kernel.org/
[2] https://lore.kernel.org/rust-for-linux/20260530132736.3298549-1-dakr@kernel.org/

Signed-off-by: Markus Probst <markus.probst@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              | 590 +++++++++++++++++++++++++++++++++++++
 samples/rust/Kconfig               |  11 +
 samples/rust/Makefile              |   1 +
 samples/rust/rust_driver_serdev.rs |  91 ++++++
 10 files changed, 730 insertions(+), 1 deletion(-)
---
base-commit: 3bc831df9ee16fceee851872315161377ca1417d
change-id: 20251217-rust_serdev-ee5481e9085c
prerequisite-message-id: 20260505152400.3905096-1-dakr@kernel.org
prerequisite-patch-id: d2aebf69b153c039bbed1d0ed26906708fd22534
prerequisite-patch-id: 84b28da2f5de20fc1785095c647b2ffc35d969a5
prerequisite-patch-id: 67318671a5eed5fb4ad23a450f1cf0e442bf8ca2
prerequisite-message-id: 20260525202921.124698-1-dakr@kernel.org
prerequisite-patch-id: b84db329d4372a175cb8d49e4e88c3eecf7eb228
prerequisite-patch-id: 2c30303f409cc8288cc87e241920219f5ddd8390
prerequisite-patch-id: 4e4f0ad370d763ad00b0f75b91fa216f2cc95953
prerequisite-patch-id: 5bcd6b37f3498feebda275dfef78136eba34004e
prerequisite-patch-id: 872b0982f3e5e7d1698d9df3b325e4cd27b27789
prerequisite-patch-id: 3a3c7749e017d9335f58497404d1350e96caf471
prerequisite-patch-id: 3526c9154f581497a11465b936d83ef61a875454
prerequisite-patch-id: 65d8c757b52475c2acc7d22ddc92cd3f0152b55d
prerequisite-patch-id: 4bd31f1414d5248dc080884caadf5f21684a8427
prerequisite-patch-id: 7beadbb0da3e589ed86d12f512d1c83427dd82b4
prerequisite-patch-id: 12cd0f67ffd27347f90c065db491945908206b7f
prerequisite-patch-id: 4642e31f66331f6c3b579377111ea733dbb3a11c
prerequisite-patch-id: 52d67b40b4396c741e2222d6a5bc7927abcb77aa
prerequisite-patch-id: 74ca82ff26cf9c7a993757c87db8be62006e820f
prerequisite-patch-id: 466fb9fa7febbffd8ef51b311c7d9893c11fc0f0
prerequisite-patch-id: e515cd98b06e26721cbbe6a4fbacd251d0073b63
prerequisite-patch-id: 8dc8e75d9f6499a554ef7e474bbacdbf3660a9f2
prerequisite-patch-id: 5fdb9f71dca2f44dd293760a60db125b770f1f55
prerequisite-patch-id: c766a24c2d5064f5ec09daada0b8e8fba862d3aa
prerequisite-patch-id: b768f6456d35fa7a80c015e34bbdba6082dbd593
prerequisite-patch-id: 6a8b17234f12f7084e6e2ce843a7031b0a891ce4
prerequisite-patch-id: 98b2deb9e60c1f28f90c5ee34fd608aaa9fd9420
prerequisite-patch-id: 774b29be66e641ee50cedb4704cf49d8b9fabf50
prerequisite-patch-id: cf95dc936cfc4b3a7a363435a51a48d9009645b3
prerequisite-message-id: 20260530132736.3298549-1-dakr@kernel.org
prerequisite-patch-id: 310c6bee038ca3909a8e5e58ec12b74f7189b869
prerequisite-patch-id: 92812c3d42b29504838e6dc66c307ff5c035bb5e

[PATCH v12 1/3] rust: add basic serial device bus abstractions

[Markus Probst via B4 Relay]

From: Markus Probst <markus.probst@posteo.de>

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           | 590 ++++++++++++++++++++++++++++++++++++++++
 7 files changed, 625 insertions(+)

diff --git a/MAINTAINERS b/MAINTAINERS
index 1a5508df3f44..d21be30a2d9d 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -24277,6 +24277,8 @@ 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 446dbeaf0866..4e42635b8607 100644
--- a/rust/bindings/bindings_helper.h
+++ b/rust/bindings/bindings_helper.h
@@ -84,6 +84,7 @@
 #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 38b34518eff1..2fb8506a748a 100644
--- a/rust/helpers/helpers.c
+++ b/rust/helpers/helpers.c
@@ -86,6 +86,7 @@
 #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 b72b2fbe046d..83bc2c312241 100644
--- a/rust/kernel/lib.rs
+++ b/rust/kernel/lib.rs
@@ -118,6 +118,8 @@
 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..ab5d6446b091
--- /dev/null
+++ b/rust/kernel/serdev.rs
@@ -0,0 +1,590 @@
+// 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;
+        }
+
+        // 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 + '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> {
+        // 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 {}
+
+// 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> {}

-- 
2.53.0

[PATCH v12 2/3] samples: rust: add Rust serial device bus sample device driver

[Markus Probst via B4 Relay]

From: Markus Probst <markus.probst@posteo.de>

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 | 91 ++++++++++++++++++++++++++++++++++++++
 4 files changed, 104 insertions(+)

diff --git a/MAINTAINERS b/MAINTAINERS
index d21be30a2d9d..3b995cb6e902 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -24279,6 +24279,7 @@ 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..824affbf6593
--- /dev/null
+++ b/samples/rust/rust_driver_serdev.rs
@@ -0,0 +1,91 @@
+// 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 {
+        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",
+}

-- 
2.53.0

[PATCH v12 3/3] MAINTAINERS: serdev: Add self for serdev

[Markus Probst via B4 Relay]

From: Markus Probst <markus.probst@posteo.de>

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/
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 3b995cb6e902..200f0ab09f9b 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -24271,7 +24271,7 @@ 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

-- 
2.53.0

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 via B4 Relay <devnull+markus.probst.posteo.de@kernel.org>
Patches: 4
Reviewed: 2026-06-04T11:33:17.504262

---

This is a well-structured v12 series adding Rust abstractions for the serial device bus (serdev). The design closely follows established Rust-for-Linux bus driver patterns (platform, USB, auxiliary). The probe/remove lifecycle is carefully handled with a `ScopeGuard` for cleanup on probe failure, and a `Mutex<bool>` (`active`) to protect against `receive_buf_callback` racing with either a failed probe or a drop. The series depends on Danilo Krummrich's driver-lifetime patches.

The code is generally clean and the safety comments are well-written. I found a few documentation typos, one questionable silent-overflow-to-infinite-timeout semantic, and a theoretical truncation issue in `write_all()`. None of these are showstoppers.

**Verdict:** Looks good with minor nits. The core abstraction design is sound.

---

---
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 adding `rust/kernel/serdev.rs`, C helpers, Kconfig, and bindings.

**1. Typo in `Parity::Even` doc (line 47 of serdev.rs):**

```rust
/// Even partiy.
Even = bindings::serdev_parity_SERDEV_PARITY_EVEN,
```

"partiy" should be "parity".

**2. `Timeout::into_jiffies` — silent overflow to infinite wait (lines 66–74):**

```rust
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,
    }
}
```

`Jiffies` is `c_ulong` (u64 on 64-bit). If a caller passes a `NonZero<Jiffies>` value exceeding `isize::MAX`, `try_into()` fails and `unwrap_or_default()` returns 0. Since `serdev_device_write()` in C treats `timeout == 0` as `MAX_SCHEDULE_TIMEOUT`, this silently converts a large-but-finite timeout into an *infinite* timeout. The user explicitly used `Timeout::Jiffies(...)` — they did not ask for `Timeout::Max`. Consider saturating to `isize::MAX` instead:

```rust
Self::Jiffies(value) => value.get().try_into().unwrap_or(isize::MAX),
```

This would cap at the largest representable finite timeout rather than silently going infinite. The same applies to the `Milliseconds` arm.

**3. `Timeout` doc string is misleading (line 53):**

```rust
/// Timeout in Jiffies.
pub enum Timeout {
```

The enum supports Jiffies, Milliseconds, and Max. The doc should say something like "Timeout for serial device operations."

**4. `write_all()` — theoretical i32 truncation of ssize_t (lines 489–504):**

```rust
pub fn write_all(&self, data: &[u8], timeout: Timeout) -> Result<usize> {
    let ret = unsafe {
        bindings::serdev_device_write(
            self.as_raw(), data.as_ptr(), data.len(), timeout.into_jiffies(),
        )
    };
    to_result(ret as i32).map(|()| ret.unsigned_abs())
}
```

`serdev_device_write` returns `ssize_t` (i64 on 64-bit). The cast `ret as i32` truncates on 64-bit. If the return value were in the range `[0x80000000, 0xFFFFFFFF]` (2–4 GB), the truncated i32 would be negative and `to_result` would incorrectly treat it as an error code. This is academic for serial devices (serial writes are never that large), but it's a latent correctness issue. The comment "negative return values are guaranteed to be between `-MAX_ERRNO` and `-1`" only covers the error case. A cleaner pattern would be:

```rust
if ret < 0 {
    return to_result(ret as i32).map(|()| 0);
}
Ok(ret as usize)
```

**5. `write()` doc — missing `[` in cross-reference (line 513):**

```rust
/// 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
```

Should be `[`Device::wait_until_sent`]` (missing opening backtick-bracket).

**6. `unbind()` doc — incomplete sentence (line 403):**

```rust
/// This callback serves as a place for drivers to perform teardown operations that require a
/// `&Device<Core>` or `&Device<Bound>` reference. For instance.
```

"For instance." is an incomplete sentence. Either provide an example or remove it.

**7. `remove_callback` does not drop PrivateData (lines 223–244):**

```rust
extern "C" fn remove_callback(sdev: *mut bindings::serdev_device) {
    let sdev = unsafe { &*sdev.cast::<Device<device::CoreInternal<'_>>>() };
    let private_data = unsafe { sdev.as_ref().drvdata_borrow::<PrivateData<'_, T>>() };
    // ... calls T::unbind, but never calls drvdata_obtain to free PrivateData
}
```

This relies on the driver-lifetime framework to drop PrivateData after the remove callback returns. This is correct per the framework design, but worth noting that the driver data (`T::Data`) is dropped via `PinnedDrop` on `PrivateData`, not via `unbind`. The ordering is: `remove_callback` calls `unbind` → framework drops `PrivateData` → `PinnedDrop` drops `T::Data` then closes the device. This is fine.

**8. Probe: receive_buf can fire before T::probe completes (lines 194–210):**

The probe sequence is: set drvdata → set client ops → open device → call `T::probe`. Since `active` starts as `false`, any `receive_buf_callback` firing between `serdev_device_open` and probe completion will see `!*active` and return `length` (discarding data). This is intentional and matches the v11 changelog ("simplify abstraction by removing ability to receive the initial transmission"). Just noting this is a design choice visible to driver authors — data arriving during probe is silently consumed and discarded.

**9. C helpers look correct:**

The three helpers (`serdev_device_driver_unregister`, `serdev_device_put`, `serdev_device_set_client_ops`) wrap inline functions / macros that can't be called directly from Rust bindgen. These are straightforward and correct.

**10. `Device<Bound>` but not `Device<Core>` for serial ops:**

All the serial operations (`set_baudrate`, `set_flow_control`, `write`, etc.) are only available on `Device<Bound>`. However, the `probe` callback receives `Device<Core<'_>>` and `Core` derefs to `Bound`, so the driver can call these methods during probe. This is consistent with the driver-lifetime pattern.

---

---
Generated by Claude Code Patch Reviewer

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

[Claude Code Review Bot]

Patch Review

This is a clean, minimal sample driver that demonstrates the serdev abstraction.

**1. Probe error handling — discards actual baudrate on error (lines 220–229):**

```rust
if sdev
    .set_baudrate(
        dev.fwnode()
            .and_then(|fwnode| fwnode.property_read(c"baudrate").optional())
            .unwrap_or(115200),
    )
    .is_err()
{
    return Err(EINVAL);
}
```

`set_baudrate` returns `Result<(), u32>` where the `Err(u32)` contains the actual baudrate that was set. The sample discards this. Fine for a sample, but a real driver might want to log or use the actual rate.

**2. `receive` callback echoes data — good illustrative choice:**

```rust
fn receive<'bound>(
    sdev: &'bound serdev::Device<Bound>,
    _this: Pin<&Self>,
    data: &[u8],
) -> usize {
    let _ = sdev.write_all(data, serdev::Timeout::Max);
    data.len()
}
```

The echo pattern is a good sample. Ignoring the `write_all` result with `let _ = ...` is acceptable here since there's no meaningful recovery in a sample echo driver.

**3. Kconfig correctly selects `RUST_SERIAL_DEV_BUS_ABSTRACTIONS`.**

No issues.

---

---
Generated by Claude Code Patch Reviewer

Claude review: MAINTAINERS: serdev: Add self for serdev

[Claude Code Review Bot]

Patch Review

```diff
-M:	Rob Herring <robh@kernel.org>
+M:	Markus Probst <markus.probst@posteo.de>
```

Straightforward maintainership change. The commit message links to the relevant discussion where Rob indicated he needs someone else to maintain serdev. This is appropriate given Markus is the author of the Rust abstractions and has been actively iterating on them (v12).

One note: this replaces Rob entirely rather than adding Markus alongside him. The linked discussion confirms Rob wants to hand off maintenance, so this appears intentional and agreed upon.

---
Generated by Claude Code Patch Reviewer

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

[Claude Code Review Bot]

Patch Review

**Inconsistent error handling for `set_baudrate`:**

```rust
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)?;
```

`set_baudrate` uses an explicit `if .is_err()` check and returns `Err(EINVAL)`, while `set_parity` uses `?` to propagate the error. This inconsistency is because `set_baudrate` returns `Result<(), u32>` (where the error value is the actual baudrate set, which can't use `?` with `Error`), but it's worth noting in a comment that the asymmetry is intentional. The `set_baudrate` API returns the actual rate set on failure rather than an error code — this is a reasonable Rust wrapper for the C semantics where `serdev_device_set_baudrate` returns the actual baudrate (0 if not set).

**The `receive` callback echoes all data back:**

```rust
fn receive<'bound>(
    sdev: &'bound serdev::Device<Bound>,
    _this: Pin<&Self>,
    data: &[u8],
) -> usize {
    let _ = sdev.write_all(data, serdev::Timeout::Max);
    data.len()
}
```

This is an echo server — fine for a sample. Ignoring the `write_all` error with `let _` is acceptable in a sample, though it always claims to have consumed all bytes regardless of whether the write succeeded. This is a reasonable simplification for demonstration purposes.

**`SampleDriver` stores `ARef<serdev::Device>`:**

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

This takes a reference-counted reference to the device in `probe`:
```rust
Ok(Self { sdev: sdev.into() })
```

This is fine — it stores a `Device<Normal>` (via the `impl_device_context_into_aref!` conversion) for use in `Drop` to print a debug message.

---
Generated by Claude Code Patch Reviewer

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 abstraction well.

```rust
+    fn receive<'bound>(
+        sdev: &'bound serdev::Device<Bound>,
+        _this: Pin<&Self>,
+        data: &[u8],
+    ) -> usize {
+        let _ = sdev.write_all(data, serdev::Timeout::Max);
+        data.len()
+    }
```

The echo-back in `receive` silently discards write errors with `let _ =`. For a sample this is acceptable, but it might be worth a brief comment or `dev_warn!` for educational purposes.

The `set_baudrate` error handling:

```rust
+        if sdev
+            .set_baudrate(...)
+            .is_err()
+        {
+            return Err(EINVAL);
+        }
```

This discards the actual baudrate returned in the `Err` variant. A more idiomatic approach would be to use `map_err` or log the actual baudrate.

---
Generated by Claude Code Patch Reviewer

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

[Claude Code Review Bot]

Patch Review

A clean sample driver demonstrating OF and ACPI device table matching, baudrate configuration from firmware properties, parity/flow control setup, and an echo-back receive callback.

**Probe error handling for `set_baudrate`:**
```rust
if sdev
    .set_baudrate(
        dev.fwnode()
            .and_then(|fwnode| fwnode.property_read(c"baudrate").optional())
            .unwrap_or(115200),
    )
    .is_err()
{
    return Err(EINVAL);
}
```
`set_baudrate` returns `Err(actual_baudrate)` when the hardware can't match the requested rate. Treating any mismatch as a hard error is fine for a sample, though real drivers may want to accept similar rates. The `if .is_err() { return Err(EINVAL) }` pattern could be simplified, but again, fine for illustration purposes.

**Receive callback silently discards write errors:**
```rust
fn receive<'bound>(
    sdev: &'bound serdev::Device<Bound>,
    _this: Pin<&Self>,
    data: &[u8],
) -> usize {
    let _ = sdev.write_all(data, serdev::Timeout::Max);
    data.len()
}
```
The `let _ =` discarding the `Result` is acceptable for a sample echo driver but would be a concern in production code. Worth a brief inline comment to note the intentional discard, since `let _ =` on a `Result` sometimes triggers lints.

**Kconfig entry:** Clean, correctly uses `select RUST_SERIAL_DEV_BUS_ABSTRACTIONS` to pull in the dependency.

---
Generated by Claude Code Patch Reviewer

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

[Claude Code Review Bot]

Patch Review

The sample is a simple echo driver — it reads a baudrate from device tree (defaulting to 115200), configures the port, and echoes back received data.

```rust
+    fn receive<'bound>(
+        sdev: &'bound serdev::Device<Bound>,
+        _this: Pin<&Self>,
+        data: &[u8],
+    ) -> usize {
+        let _ = sdev.write_all(data, serdev::Timeout::Max);
+        data.len()
+    }
```

The `let _ = ...` explicitly discards the write result, which is acceptable for a sample. The function always returns `data.len()` claiming all data was consumed regardless of write success — fine for demonstration purposes.

**Nit:** The `set_baudrate` error handling:
```rust
+        if sdev
+            .set_baudrate(
+                dev.fwnode()
+                    .and_then(|fwnode| fwnode.property_read(c"baudrate").optional())
+                    .unwrap_or(115200),
+            )
+            .is_err()
+        {
+            return Err(EINVAL);
```
The `Err(u32)` from `set_baudrate` (containing the actual baudrate that was set) is discarded. A `dev_warn!` logging the mismatch would be helpful for debugging, but not required for a sample.

The `// ` trailing comments on some import lines are unusual formatting artifacts (likely from rustfmt vertical formatting). Not a functional issue.

---

---
Generated by Claude Code Patch Reviewer