[PATCH net v3] rust: net: phy: fix off-by-one bit positions in device status accessors

The hand-written bitfield offsets in is_link_up(), is_autoneg_enabled()
and is_autoneg_completed() were correct when the abstraction was
merged: at that time autoneg, link, and autoneg_complete were at bits
13, 14, and 15 of struct phy_device's first bitfield unit. Commit
2796ff1e3dca ("net: phy: add flag is_genphy_driven to struct
phy_device") later inserted is_genphy_driven just before autoneg,
shifting the three fields up by one, so the accessors now read:

  is_link_up()           reads bit 14 = autoneg
  is_autoneg_enabled()   reads bit 13 = is_genphy_driven
  is_autoneg_completed() reads bit 15 = link

The official ax88796b Rust driver uses all three accessors in its
link-change handling, so it inherits the bug. On genphy-driven devices
is_genphy_driven is always 1, which masks the broken
is_autoneg_enabled() check.

Hard-coded offsets will silently break again on the next layout
change, so use the bindgen-generated accessors (link(), autoneg(),
autoneg_complete()), which are always consistent with the C layout,
and drop the hand-written numbers together with the TODO comment that
marked them as a stopgap.

Found by a static equivalence audit (C2RustDrv, a C-to-Rust driver
migration tool) that compares hand-written bitfield offsets against
the bindgen layout of struct phy_device. Verified by building the
bindings and checking the generated accessors; no runtime testing was
possible without PHY hardware.

Fixes: 2796ff1e3dca ("net: phy: add flag is_genphy_driven to struct phy_device")
Cc: stable@vger.kernel.org
Signed-off-by: Chunfeng Song <redacted>
---
v2 -> v3:
  - Drop the links to previous versions from the commit message
    (Miguel Ojeda).
  - Keep the changelog here, after the separator, as is customary.

v1 -> v2:
  - Use the bindgen-generated accessors (link(), autoneg(),
    autoneg_complete()) instead of the hard-coded bit numbers, as
    suggested by Andrew Lunn, since the offsets drift whenever the
    layout changes.
  - Update the Fixes: tag to 2796ff1e3dca, the commit that inserted
    is_genphy_driven and shifted the fields (the offsets were correct
    when the abstraction was merged in v6.8).
  - Add the net tree prefix to the subject.

rust/kernel/net/phy.rs | 20 ++++++--------------
 1 file changed, 6 insertions(+), 14 deletions(-)

diff --git a/rust/kernel/net/phy.rs b/rust/kernel/net/phy.rs
index 956cda573ddb..14dd1e6cb380 100644
--- a/rust/kernel/net/phy.rs
+++ b/rust/kernel/net/phy.rs

@@ -124,38 +124,30 @@ pub fn state(&self) -> DeviceState {
     ///
     /// It returns true if the link is up.
     pub fn is_link_up(&self) -> bool {
-        const LINK_IS_UP: u64 = 1;
-        // TODO: the code to access to the bit field will be replaced with automatically
-        // generated code by bindgen when it becomes possible.
+        let phydev = self.0.get();
         // SAFETY: The struct invariant ensures that we may access
         // this field without additional synchronization.
-        let bit_field = unsafe { &(*self.0.get())._bitfield_1 };
-        bit_field.get(14, 1) == LINK_IS_UP
+        unsafe { (*phydev).link() == 1 }
     }
 
     /// Gets the current auto-negotiation configuration.
     ///
     /// It returns true if auto-negotiation is enabled.
     pub fn is_autoneg_enabled(&self) -> bool {
-        // TODO: the code to access to the bit field will be replaced with automatically
-        // generated code by bindgen when it becomes possible.
+        let phydev = self.0.get();
         // SAFETY: The struct invariant ensures that we may access
         // this field without additional synchronization.
-        let bit_field = unsafe { &(*self.0.get())._bitfield_1 };
-        bit_field.get(13, 1) == u64::from(bindings::AUTONEG_ENABLE)
+        unsafe { (*phydev).autoneg() == bindings::AUTONEG_ENABLE }
     }
 
     /// Gets the current auto-negotiation state.
     ///
     /// It returns true if auto-negotiation is completed.
     pub fn is_autoneg_completed(&self) -> bool {
-        const AUTONEG_COMPLETED: u64 = 1;
-        // TODO: the code to access to the bit field will be replaced with automatically
-        // generated code by bindgen when it becomes possible.
+        let phydev = self.0.get();
         // SAFETY: The struct invariant ensures that we may access
         // this field without additional synchronization.
-        let bit_field = unsafe { &(*self.0.get())._bitfield_1 };
-        bit_field.get(15, 1) == AUTONEG_COMPLETED
+        unsafe { (*phydev).autoneg_complete() == 1 }
     }
 
     /// Sets the speed of the PHY.

-- 
2.43.0