[PATCH v4 3/3] samples: rust: add Rust I2C sample driver

[Igor Korotin <igor.korotin.linux@gmail.com>]

Add a new `rust_driver_i2c` sample, showing how to create a new
i2c client using `i2c::Registration` and bind a driver to it
via legacy I2C-ID table.

Signed-off-by: Igor Korotin <igor.korotin.linux@gmail.com>
---
 MAINTAINERS                     |   1 +
 samples/rust/Kconfig            |  11 +++
 samples/rust/Makefile           |   1 +
 samples/rust/rust_driver_i2c.rs | 128 ++++++++++++++++++++++++++++++++
 4 files changed, 141 insertions(+)
 create mode 100644 samples/rust/rust_driver_i2c.rs

diff --git a/MAINTAINERS b/MAINTAINERS
index c44c7ac317b1..2654a7ea0c80 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -11523,6 +11523,7 @@ R:	Daniel Almeida <daniel.almeida@collabora.com>
 L:	rust-for-linux@vger.kernel.org
 S:	Maintained
 F:	rust/kernel/i2c.rs
+F:	samples/rust/rust_driver_i2c.rs
 
 I2C SUBSYSTEM HOST DRIVERS
 M:	Andi Shyti <andi.shyti@kernel.org>
diff --git a/samples/rust/Kconfig b/samples/rust/Kconfig
index 7f7371a004ee..28dae070b365 100644
--- a/samples/rust/Kconfig
+++ b/samples/rust/Kconfig
@@ -62,6 +62,17 @@ config SAMPLE_RUST_DMA
 
 	  If unsure, say N.
 
+config SAMPLE_RUST_DRIVER_I2C
+	tristate "I2C Driver"
+	depends on I2C=y
+	help
+	  This option builds the Rust I2C driver sample.
+
+	  To compile this as a module, choose M here:
+	  the module will be called rust_driver_i2c.
+
+	  If unsure, say N.
+
 config SAMPLE_RUST_DRIVER_PCI
 	tristate "PCI Driver"
 	depends on PCI
diff --git a/samples/rust/Makefile b/samples/rust/Makefile
index bd2faad63b4f..141d8f078248 100644
--- a/samples/rust/Makefile
+++ b/samples/rust/Makefile
@@ -5,6 +5,7 @@ obj-$(CONFIG_SAMPLE_RUST_MINIMAL)		+= rust_minimal.o
 obj-$(CONFIG_SAMPLE_RUST_MISC_DEVICE)		+= rust_misc_device.o
 obj-$(CONFIG_SAMPLE_RUST_PRINT)			+= rust_print.o
 obj-$(CONFIG_SAMPLE_RUST_DMA)			+= rust_dma.o
+obj-$(CONFIG_SAMPLE_RUST_DRIVER_I2C)		+= rust_driver_i2c.o
 obj-$(CONFIG_SAMPLE_RUST_DRIVER_PCI)		+= rust_driver_pci.o
 obj-$(CONFIG_SAMPLE_RUST_DRIVER_PLATFORM)	+= rust_driver_platform.o
 obj-$(CONFIG_SAMPLE_RUST_DRIVER_FAUX)		+= rust_driver_faux.o
diff --git a/samples/rust/rust_driver_i2c.rs b/samples/rust/rust_driver_i2c.rs
new file mode 100644
index 000000000000..6dfc299d5aea
--- /dev/null
+++ b/samples/rust/rust_driver_i2c.rs
@@ -0,0 +1,128 @@
+// SPDX-License-Identifier: GPL-2.0
+
+//! Rust I2C driver sample.
+//!
+//! This module shows how to:
+//!
+//! 1. Manually create an `i2c_client` at address `SAMPLE_I2C_CLIENT_ADDR`
+//!    on the adapter with index `SAMPLE_I2C_ADAPTER_INDEX`.
+//! 2. Register a matching Rust-based I2C driver for that client.
+//!
+//! # Requirements
+//!
+//! - The target system must expose an I2C adapter at index
+//!   `SAMPLE_I2C_ADAPTER_INDEX`.
+//! - To emulate an adapter for testing, you can load the
+//!   `i2c-stub` kernel module with an option `chip_addr`
+//!   For example for this sample driver to emulate an I2C device with
+//!   an address 0x30 you can use:
+//!      `modprobe i2c-stub chip_addr=0x30`
+//!
+
+use kernel::{
+    acpi, c_str,
+    device::{Core, Normal},
+    i2c, of,
+    prelude::*,
+    types::ARef,
+};
+
+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);
+
+struct SampleDriver {
+    pdev: ARef<i2c::I2cClient>,
+}
+
+kernel::acpi_device_table! {
+    ACPI_TABLE,
+    MODULE_ACPI_TABLE,
+    <SampleDriver as i2c::Driver>::IdInfo,
+    [(acpi::DeviceId::new(c_str!("LNUXBEEF")), 0)]
+}
+
+kernel::i2c_device_table! {
+    I2C_TABLE,
+    MODULE_I2C_TABLE,
+    <SampleDriver as i2c::Driver>::IdInfo,
+    [(i2c::DeviceId::new(c_str!("rust_driver_i2c")), 0)]
+}
+
+kernel::of_device_table! {
+    OF_TABLE,
+    MODULE_OF_TABLE,
+    <SampleDriver as i2c::Driver>::IdInfo,
+    [(of::DeviceId::new(c_str!("test,rust_driver_i2c")), 0)]
+}
+
+impl i2c::Driver for SampleDriver {
+    type IdInfo = u32;
+
+    const ACPI_ID_TABLE: Option<acpi::IdTable<Self::IdInfo>> = Some(&ACPI_TABLE);
+    const I2C_ID_TABLE: Option<i2c::IdTable<Self::IdInfo>> = Some(&I2C_TABLE);
+    const OF_ID_TABLE: Option<of::IdTable<Self::IdInfo>> = Some(&OF_TABLE);
+
+    fn probe(pdev: &i2c::I2cClient<Core>, info: Option<&Self::IdInfo>) -> Result<Pin<KBox<Self>>> {
+        let dev = pdev.as_ref();
+
+        dev_dbg!(dev, "Probe Rust I2C driver sample.\n");
+
+        if let Some(info) = info {
+            dev_info!(dev, "Probed with info: '{}'.\n", info);
+        }
+
+        let drvdata = KBox::new(Self { pdev: pdev.into() }, GFP_KERNEL)?;
+
+        Ok(drvdata.into())
+    }
+
+    fn shutdown(pdev: &i2c::I2cClient<Core>) {
+        dev_dbg!(pdev.as_ref(), "Shutdown Rust I2C driver sample.\n");
+    }
+}
+
+impl Drop for SampleDriver {
+    fn drop(&mut self) {
+        dev_dbg!(self.pdev.as_ref(), "Remove Rust I2C driver sample.\n");
+    }
+}
+
+// NOTE: The code below is expanded macro module_i2c_driver. It is not used here
+//       because we need to manually create an I2C client in `init()`. The macro
+//       hides `init()`, so to demo client creation on adapter SAMPLE_I2C_ADAPTER_INDEX
+//       we expand it by hand.
+type Ops<T> = kernel::i2c::Adapter<T>;
+
+#[pin_data]
+struct DriverModule {
+    #[pin]
+    _driver: kernel::driver::Registration<Ops<SampleDriver>>,
+    _reg: i2c::Registration,
+}
+
+impl kernel::InPlaceModule for DriverModule {
+    fn init(
+        module: &'static kernel::ThisModule,
+    ) -> impl ::pin_init::PinInit<Self, kernel::error::Error> {
+        kernel::try_pin_init!(Self {
+            _reg <- {
+                let adapter = i2c::I2cAdapter::<Normal>::get(SAMPLE_I2C_ADAPTER_INDEX)?;
+
+                i2c::Registration::new(adapter, &BOARD_INFO)
+            },
+            _driver <- kernel::driver::Registration::new(
+                 <Self as kernel::ModuleMetadata>::NAME, module
+            ),
+        })
+    }
+}
+
+kernel::prelude::module! {
+    type: DriverModule,
+    name: "rust_driver_i2c",
+    authors: ["Igor Korotin"],
+    description: "Rust I2C driver",
+    license: "GPL v2",
+}
-- 
2.43.0