samples: rust: add Rust I2C client registration sample

Add a new `rust_i2c_client` sample, showing how to create a new
i2c client using `i2c::Registration`

Acked-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Signed-off-by: Igor Korotin <igor.korotin.linux@gmail.com>
Link: https://patch.msgid.link/20251116162210.171542-1-igor.korotin.linux@gmail.com
[ * Remove dependency to I2C_CHARDEV, depend on I2C=y.
  * Remove unnecessary impl Drop for SampleDriver.
  * Rename i2c::Registration, import Devres.
  * Fixup module description.
  * Add new source file to MAINTAINERS.
  - Danilo ]
Signed-off-by: Danilo Krummrich <dakr@kernel.org>

MAINTAINERS

@@ -11751,6 +11751,7 @@ L:	rust-for-linux@vger.kernel.org
 S:	Maintained
 F:	rust/kernel/i2c.rs
 F:	samples/rust/rust_driver_i2c.rs
+F:	samples/rust/rust_i2c_client.rs
 
 I2C SUBSYSTEM HOST DRIVERS
 M:	Andi Shyti <andi.shyti@kernel.org>

samples/rust/Kconfig

@@ -95,6 +95,18 @@ config SAMPLE_RUST_DRIVER_I2C
 
 	  If unsure, say N.
 
+config SAMPLE_RUST_I2C_CLIENT
+	tristate "I2C Client Registration"
+	depends on I2C=y
+	help
+	  This option builds the Rust I2C client manual creation
+	  sample.
+
+	  To compile this as a module, choose M here:
+	  the module will be called rust_i2c_client.
+
+	  If unsure, say N.
+
 config SAMPLE_RUST_DRIVER_PCI
 	tristate "PCI Driver"
 	depends on PCI

samples/rust/Makefile

@@ -8,6 +8,7 @@ obj-$(CONFIG_SAMPLE_RUST_DEBUGFS)		+= rust_debugfs.o
 obj-$(CONFIG_SAMPLE_RUST_DEBUGFS_SCOPED)	+= rust_debugfs_scoped.o
 obj-$(CONFIG_SAMPLE_RUST_DMA)			+= rust_dma.o
 obj-$(CONFIG_SAMPLE_RUST_DRIVER_I2C)		+= rust_driver_i2c.o
+obj-$(CONFIG_SAMPLE_RUST_I2C_CLIENT)		+= rust_i2c_client.o
 obj-$(CONFIG_SAMPLE_RUST_DRIVER_PCI)		+= rust_driver_pci.o
 obj-$(CONFIG_SAMPLE_RUST_DRIVER_PLATFORM)	+= rust_driver_platform.o
 obj-$(CONFIG_SAMPLE_RUST_DRIVER_USB)		+= rust_driver_usb.o

samples/rust/rust_i2c_client.rs

@@ -0,0 +1,147 @@
+// SPDX-License-Identifier: GPL-2.0
+
+//! Rust I2C client registration sample.
+//!
+//! An I2C client in Rust cannot exist on its own. To register a new I2C client,
+//! it must be bound to a parent device. In this sample driver, a platform device
+//! is used as the parent.
+//!
+
+//! ACPI match table test
+//!
+//! This demonstrates how to test an ACPI-based Rust I2C client registration driver
+//! using QEMU with a custom SSDT.
+//!
+//! Steps:
+//!
+//! 1. **Create an SSDT source file** (`ssdt.dsl`) with the following content:
+//!
+//!     ```asl
+//!     DefinitionBlock ("", "SSDT", 2, "TEST", "VIRTACPI", 0x00000001)
+//!     {
+//!         Scope (\_SB)
+//!         {
+//!             Device (T432)
+//!             {
+//!                 Name (_HID, "LNUXBEEF")  // ACPI hardware ID to match
+//!                 Name (_UID, 1)
+//!                 Name (_STA, 0x0F)        // Device present, enabled
+//!                 Name (_CRS, ResourceTemplate ()
+//!                 {
+//!                     Memory32Fixed (ReadWrite, 0xFED00000, 0x1000)
+//!                 })
+//!             }
+//!         }
+//!     }
+//!     ```
+//!
+//! 2. **Compile the table**:
+//!
+//!     ```sh
+//!     iasl -tc ssdt.dsl
+//!     ```
+//!
+//!     This generates `ssdt.aml`
+//!
+//! 3. **Run QEMU** with the compiled AML file:
+//!
+//!     ```sh
+//!     qemu-system-x86_64 -m 512M \
+//!         -enable-kvm \
+//!         -kernel path/to/bzImage \
+//!         -append "root=/dev/sda console=ttyS0" \
+//!         -hda rootfs.img \
+//!         -serial stdio \
+//!         -acpitable file=ssdt.aml
+//!     ```
+//!
+//!     Requirements:
+//!     - The `rust_driver_platform` must be present either:
+//!         - built directly into the kernel (`bzImage`), or
+//!         - available as a `.ko` file and loadable from `rootfs.img`
+//!
+//! 4. **Verify it worked** by checking `dmesg`:
+//!
+//!     ```
+//!     rust_driver_platform LNUXBEEF:00: Probed with info: '0'.
+//!     ```
+//!
+
+use kernel::{
+    acpi,
+    c_str,
+    device,
+    devres::Devres,
+    i2c,
+    of,
+    platform,
+    prelude::*,
+    sync::aref::ARef, //
+};
+
+#[pin_data]
+struct SampleDriver {
+    parent_dev: ARef<platform::Device>,
+    #[pin]
+    _reg: Devres<i2c::Registration>,
+}
+
+kernel::of_device_table!(
+    OF_TABLE,
+    MODULE_OF_TABLE,
+    <SampleDriver as platform::Driver>::IdInfo,
+    [(of::DeviceId::new(c_str!("test,rust-device")), ())]
+);
+
+kernel::acpi_device_table!(
+    ACPI_TABLE,
+    MODULE_ACPI_TABLE,
+    <SampleDriver as platform::Driver>::IdInfo,
+    [(acpi::DeviceId::new(c_str!("LNUXBEEF")), ())]
+);
+
+const SAMPLE_I2C_CLIENT_ADDR: u16 = 0x30;
+const SAMPLE_I2C_ADAPTER_INDEX: i32 = 0;
+const BOARD_INFO: i2c::I2cBoardInfo =
+    i2c::I2cBoardInfo::new(c_str!("rust_driver_i2c"), SAMPLE_I2C_CLIENT_ADDR);
+
+impl platform::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(
+        pdev: &platform::Device<device::Core>,
+        _info: Option<&Self::IdInfo>,
+    ) -> impl PinInit<Self, Error> {
+        dev_info!(
+            pdev.as_ref(),
+            "Probe Rust I2C Client registration sample.\n"
+        );
+
+        kernel::try_pin_init!( Self {
+            parent_dev: pdev.into(),
+
+            _reg <- {
+                let adapter = i2c::I2cAdapter::get(SAMPLE_I2C_ADAPTER_INDEX)?;
+
+                i2c::Registration::new(&adapter, &BOARD_INFO, pdev.as_ref())
+            }
+        })
+    }
+
+    fn unbind(pdev: &platform::Device<device::Core>, _this: Pin<&Self>) {
+        dev_info!(
+            pdev.as_ref(),
+            "Unbind Rust I2C Client registration sample.\n"
+        );
+    }
+}
+
+kernel::module_platform_driver! {
+    type: SampleDriver,
+    name: "rust_device_i2c",
+    authors: ["Danilo Krummrich", "Igor Korotin"],
+    description: "Rust I2C client registration",
+    license: "GPL v2",
+}