rust: net: phy: fix off-by-one bit positions in device status accessors

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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
2796ff1e3d ("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
read_status() implementation, so it inherits the bug.
phy_attach_direct() sets is_genphy_driven only when it falls back to
the generic driver, and ax88796b has a real driver, so
is_genphy_driven stays 0. The broken is_autoneg_enabled() therefore
reads bit 13 as 0, compares it against AUTONEG_ENABLE (1), and always
returns false, so read_status() never reaches the
resolve_aneg_linkmode() call.

The ordinary bindgen accessors take &self. Calling them through
(*phydev).link() would create a shared reference to the complete
bindings::phy_device, which is not appropriate for an object wrapped in
Opaque.

Use the bindgen-generated raw accessors (link_raw(), autoneg_raw(),
and autoneg_complete_raw()) instead. They retain the bit positions and
endianness handling generated from the C layout without creating a Rust
reference to the complete phy_device. Drop the hand-written numbers
together with the TODO comment that marked them as a stopgap.

The raw accessors are only emitted by bindgen 0.71 and later, and were
added at the Rust-for-Linux project's request, so this fix can only be
backported to stable branches whose minimum bindgen version is at least
that, hence the scope on the Cc: stable line below.

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: 2796ff1e3d ("net: phy: add flag is_genphy_driven to struct phy_device")
Cc: stable@vger.kernel.org # Only 7.1.y and later (requires bindgen's raw pointer accessors).
Link: https://github.com/rust-lang/rust-bindgen/issues/2674
Signed-off-by: Chunfeng Song <springbreeze@stu.pku.edu.cn>
Reviewed-by: FUJITA Tomonori <fujita.tomonori@gmail.com>
Link: https://patch.msgid.link/20260910055110.167110-1-springbreeze@stu.pku.edu.cn
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

...

This commit is contained in:

Chunfeng Song 2026-09-10 05:51:10 +00:00 • committed by Jakub Kicinski

parent f97d8c7bab

commit 6fb0a9d907

1 changed files with 18 additions and 20 deletions

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rust/kernel/net/phy.rs

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