rust: pci: fix unrestricted &mut pci::Device

As by now, pci::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 pci::Device as

	pub struct Device<Ctx: DeviceContext = Normal>(
		Opaque<bindings::pci_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 pci::Device<Core>. Consequently, we
make this type accessible in bus callbacks only.

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

Fixes: 1bd8b6b2c5d3 ("rust: pci: add basic PCI 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/20250314160932.100165-4-dakr@kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 4 insertions, 4 deletions

diff --git a/samples/rust/rust_driver_pci.rs b/samples/rust/rust_driver_pci.rs
index ddc52db71a82..6cee912b6a66 100644
--- a/samples/rust/rust_driver_pci.rs
+++ b/samples/rust/rust_driver_pci.rs
@@ -4,7 +4,7 @@
 //!
 //! To make this driver probe, QEMU must be run with `-device pci-testdev`.
 
-use kernel::{bindings, c_str, devres::Devres, pci, prelude::*};
+use kernel::{bindings, c_str, device::Core, devres::Devres, pci, prelude::*, types::ARef};
 
 struct Regs;
 
@@ -26,7 +26,7 @@ impl TestIndex {
 }
 
 struct SampleDriver {
-    pdev: pci::Device,
+    pdev: ARef<pci::Device>,
     bar: Devres<Bar0>,
 }
 
@@ -62,7 +62,7 @@ impl pci::Driver for SampleDriver {
 
     const ID_TABLE: pci::IdTable<Self::IdInfo> = &PCI_TABLE;
 
-    fn probe(pdev: &mut pci::Device, info: &Self::IdInfo) -> Result<Pin<KBox<Self>>> {
+    fn probe(pdev: &pci::Device<Core>, info: &Self::IdInfo) -> Result<Pin<KBox<Self>>> {
         dev_dbg!(
             pdev.as_ref(),
             "Probe Rust PCI driver sample (PCI ID: 0x{:x}, 0x{:x}).\n",
@@ -77,7 +77,7 @@ impl pci::Driver for SampleDriver {
 
         let drvdata = KBox::new(
             Self {
-                pdev: pdev.clone(),
+                pdev: pdev.into(),
                 bar,
             },
             GFP_KERNEL,