[PATCH 7/7] rust: sample: misc: implement device driver sample

[Danilo Krummrich <dakr@kernel.org>]

In order to demonstrate and test a MiscDeviceRegistration with a parent
device, introduce CONFIG_SAMPLE_RUST_MISC_DEVICE_WITH_PARENT.

If CONFIG_SAMPLE_RUST_MISC_DEVICE_WITH_PARENT=y the misc device sample
is initialized with a parent device (faux), otherwise it is initialized
without a parent device, i.e. the exact same way as without this patch.

Signed-off-by: Danilo Krummrich <dakr@kernel.org>
---
 samples/rust/Kconfig             |  8 +++++
 samples/rust/rust_misc_device.rs | 50 +++++++++++++++++++++++++++++---
 2 files changed, 54 insertions(+), 4 deletions(-)

diff --git a/samples/rust/Kconfig b/samples/rust/Kconfig
index b1006ab4bc3c..9948ec0939ef 100644
--- a/samples/rust/Kconfig
+++ b/samples/rust/Kconfig
@@ -30,6 +30,14 @@ config SAMPLE_RUST_MISC_DEVICE
 
 	  If unsure, say N.
 
+config SAMPLE_RUST_MISC_DEVICE_WITH_PARENT
+	bool "Create a misc device with a parent device"
+	depends on SAMPLE_RUST_MISC_DEVICE
+	default n
+	help
+	  Say Y here if you want the misc device sample to create a misc
+	  device with a parent device.
+
 config SAMPLE_RUST_PRINT
 	tristate "Printing macros"
 	help
diff --git a/samples/rust/rust_misc_device.rs b/samples/rust/rust_misc_device.rs
index 9bf1a0f64e6e..175638d6d341 100644
--- a/samples/rust/rust_misc_device.rs
+++ b/samples/rust/rust_misc_device.rs
@@ -167,6 +167,9 @@
     uaccess::{UserSlice, UserSliceReader, UserSliceWriter},
 };
 
+#[cfg(CONFIG_SAMPLE_RUST_MISC_DEVICE_WITH_PARENT)]
+use kernel::faux;
+
 const RUST_MISC_DEV_HELLO: u32 = _IO('|' as u32, 0x80);
 const RUST_MISC_DEV_GET_VALUE: u32 = _IOR::<i32>('|' as u32, 0x81);
 const RUST_MISC_DEV_SET_VALUE: u32 = _IOW::<i32>('|' as u32, 0x82);
@@ -181,19 +184,33 @@
     license: "GPL",
 }
 
+#[cfg(not(CONFIG_SAMPLE_RUST_MISC_DEVICE_WITH_PARENT))]
 #[pin_data]
 struct RustMiscDeviceModule {
     #[pin]
     _miscdev: MiscDeviceRegistration<RustMiscDevice>,
 }
 
-impl kernel::InPlaceModule for RustMiscDeviceModule {
-    fn init(_module: &'static ThisModule) -> impl PinInit<Self, Error> {
+#[cfg(CONFIG_SAMPLE_RUST_MISC_DEVICE_WITH_PARENT)]
+struct RustMiscDeviceModule {
+    _faux: faux::Registration,
+    _miscdev: Pin<KBox<MiscDeviceRegistration<RustMiscDevice>>>,
+}
+
+impl RustMiscDeviceModule {
+    fn init() -> MiscDeviceOptions {
         pr_info!("Initializing Rust Misc Device Sample\n");
 
-        let options = MiscDeviceOptions {
+        MiscDeviceOptions {
             name: c_str!("rust-misc-device"),
-        };
+        }
+    }
+}
+
+#[cfg(not(CONFIG_SAMPLE_RUST_MISC_DEVICE_WITH_PARENT))]
+impl kernel::InPlaceModule for RustMiscDeviceModule {
+    fn init(_module: &'static ThisModule) -> impl PinInit<Self, Error> {
+        let options = Self::init();
 
         try_pin_init!(Self {
             _miscdev <- MiscDeviceRegistration::register(
@@ -205,6 +222,31 @@ fn init(_module: &'static ThisModule) -> impl PinInit<Self, Error> {
     }
 }
 
+#[cfg(CONFIG_SAMPLE_RUST_MISC_DEVICE_WITH_PARENT)]
+impl kernel::Module for RustMiscDeviceModule {
+    fn init(_module: &'static ThisModule) -> Result<Self> {
+        let options = Self::init();
+        let faux = faux::Registration::new(c_str!("rust-misc-device-sample"), None)?;
+
+        // For every other bus, this would be called from Driver::probe(), which would return a
+        // `Result<Pin<KBox<T>>>`, but faux always binds to a "dummy" driver, hence probe() is
+        // not required.
+        let misc = KBox::pin_init(
+            MiscDeviceRegistration::register(
+                options,
+                Arc::pin_init(new_mutex!(Inner { value: 0_i32 }), GFP_KERNEL),
+                Some(faux.as_ref()),
+            ),
+            GFP_KERNEL,
+        )?;
+
+        Ok(Self {
+            _faux: faux,
+            _miscdev: misc,
+        })
+    }
+}
+
 struct Inner {
     value: i32,
 }
-- 
2.49.0