[PATCH] 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() are all one bit short of the actual layout of
struct phy_device. Counting from the first bitfield in the unit
(is_c45 at bit 0), the C definition places autoneg at bit 14,
link at bit 15, and autoneg_complete at bit 16. The accessors instead
read bits 13, 14, and 15, i.e.:

  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 partially masks the broken
is_autoneg_enabled() check and likely explains why this survived the
original netdev review rounds of the PHY abstractions, which fixed
reference/aliasing issues but never verified the bit numbers against
the C layout.

Fixes: f20fd5449ada ("rust: core abstractions for network PHY drivers")
Link: https://www.spinics.net/lists/netdev/msg951815.html (v8 cover letter, where the bitfield access was flagged as needing a fix)
Signed-off-by: Chunfeng Song <[email protected]>
---
 rust/kernel/net/phy.rs | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/rust/kernel/net/phy.rs b/rust/kernel/net/phy.rs
index 956cda573ddb..99ed3dd168df 100644
--- a/rust/kernel/net/phy.rs
+++ b/rust/kernel/net/phy.rs
@@ -130,7 +130,7 @@ pub fn is_link_up(&self) -> bool {
         // 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
+        bit_field.get(15, 1) == LINK_IS_UP
     }
 
     /// Gets the current auto-negotiation configuration.
@@ -142,7 +142,7 @@ pub fn is_autoneg_enabled(&self) -> bool {
         // 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)
+        bit_field.get(14, 1) == u64::from(bindings::AUTONEG_ENABLE)
     }
 
     /// Gets the current auto-negotiation state.
@@ -155,7 +155,7 @@ pub fn is_autoneg_completed(&self) -> bool {
         // 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
+        bit_field.get(16, 1) == AUTONEG_COMPLETED
     }
 
     /// Sets the speed of the PHY.
-- 
2.43.0