rust: platform: fix unrestricted &mut platform::Device

As by now, platform::Device is implemented as:

	#[derive(Clone)]
	pub struct Device(ARef<device::Device>);

This may be convenient, but has the implication that drivers can call
device methods that require a mutable reference concurrently at any
point of time.

Instead define platform::Device as

	pub struct Device<Ctx: DeviceContext = Normal>(
		Opaque<bindings::platform_dev>,
		PhantomData<Ctx>,
	);

and manually implement the AlwaysRefCounted trait.

With this we can implement methods that should only be called from
bus callbacks (such as probe()) for platform::Device<Core>. Consequently,
we make this type accessible in bus callbacks only.

Arbitrary references taken by the driver are still of type
ARef<platform::Device> and hence don't provide access to methods that are
reserved for bus callbacks.

Fixes: 683a63befc73 ("rust: platform: add basic platform device / driver abstractions")
Reviewed-by: Benno Lossin <benno.lossin@proton.me>
Signed-off-by: Danilo Krummrich <dakr@kernel.org>
Acked-by: Boqun Feng <boqun.feng@gmail.com>
Link: https://lore.kernel.org/r/20250314160932.100165-5-dakr@kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 7 insertions, 4 deletions

diff --git a/samples/rust/rust_driver_platform.rs b/samples/rust/rust_driver_platform.rs
index 8120609e2940..9bb66db0a4f4 100644
--- a/samples/rust/rust_driver_platform.rs
+++ b/samples/rust/rust_driver_platform.rs
@@ -2,10 +2,10 @@
 
 //! Rust Platform driver sample.
 
-use kernel::{c_str, of, platform, prelude::*};
+use kernel::{c_str, device::Core, of, platform, prelude::*, types::ARef};
 
 struct SampleDriver {
-    pdev: platform::Device,
+    pdev: ARef<platform::Device>,
 }
 
 struct Info(u32);
@@ -21,14 +21,17 @@ impl platform::Driver for SampleDriver {
     type IdInfo = Info;
     const OF_ID_TABLE: Option<of::IdTable<Self::IdInfo>> = Some(&OF_TABLE);
 
-    fn probe(pdev: &mut platform::Device, info: Option<&Self::IdInfo>) -> Result<Pin<KBox<Self>>> {
+    fn probe(
+        pdev: &platform::Device<Core>,
+        info: Option<&Self::IdInfo>,
+    ) -> Result<Pin<KBox<Self>>> {
         dev_dbg!(pdev.as_ref(), "Probe Rust Platform driver sample.\n");
 
         if let Some(info) = info {
             dev_info!(pdev.as_ref(), "Probed with info: '{}'.\n", info.0);
         }
 
-        let drvdata = KBox::new(Self { pdev: pdev.clone() }, GFP_KERNEL)?;
+        let drvdata = KBox::new(Self { pdev: pdev.into() }, GFP_KERNEL)?;
 
         Ok(drvdata.into())
     }