[PATCH 2/4] rust: phy: add paged register access and bit manipulation helpers

[Artem Lytkin <iprintercanon@gmail.com>]

Add Device methods for register manipulation beyond simple read/write:

  - write_paged(): Writes a register on a specific page, completing
    the paged access surface (read_paged already existed upstream).
    Wraps phy_write_paged().

  - modify() / modify_paged(): Atomic read-modify-write operations
    that clear bits in mask and set bits in set. Wraps phy_modify()
    and phy_modify_paged(). These return Result (not the old register
    value) since the C functions return 0 on success.

  - set_bits() / clear_bits(): Convenience wrappers around modify()
    for the common case of setting or clearing specific bits.

These helpers are heavily used by real-world PHY drivers for
configuring vendor-specific registers without races.

Signed-off-by: Artem Lytkin <iprintercanon@gmail.com>
---
 rust/kernel/net/phy.rs | 43 ++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 43 insertions(+)

diff --git a/rust/kernel/net/phy.rs b/rust/kernel/net/phy.rs
index 646b2a78a2710..43d1ee360268b 100644
--- a/rust/kernel/net/phy.rs
+++ b/rust/kernel/net/phy.rs
@@ -241,6 +241,49 @@ pub fn read_paged(&mut self, page: u16, regnum: u16) -> Result<u16> {
         to_result(ret).map(|()| ret as u16)
     }
 
+    /// Writes a paged register.
+    pub fn write_paged(&mut self, page: u16, regnum: u16, val: u16) -> Result {
+        let phydev = self.0.get();
+        // SAFETY: `phydev` is pointing to a valid object by the type invariant of `Self`.
+        // So it's just an FFI call.
+        let ret =
+            unsafe { bindings::phy_write_paged(phydev, page.into(), regnum.into(), val) };
+
+        to_result(ret)
+    }
+
+    /// Performs a read-modify-write on a PHY register.
+    ///
+    /// Clears the bits set in `mask` and sets the bits in `set`.
+    pub fn modify(&mut self, regnum: u16, mask: u16, set: u16) -> Result {
+        let phydev = self.0.get();
+        // SAFETY: `phydev` is pointing to a valid object by the type invariant of `Self`.
+        // So it's just an FFI call.
+        to_result(unsafe { bindings::phy_modify(phydev, regnum.into(), mask, set) })
+    }
+
+    /// Performs a read-modify-write on a paged PHY register.
+    ///
+    /// Selects the page, performs the modify, and restores the original page.
+    pub fn modify_paged(&mut self, page: u16, regnum: u16, mask: u16, set: u16) -> Result {
+        let phydev = self.0.get();
+        // SAFETY: `phydev` is pointing to a valid object by the type invariant of `Self`.
+        // So it's just an FFI call.
+        to_result(unsafe {
+            bindings::phy_modify_paged(phydev, page.into(), regnum.into(), mask, set)
+        })
+    }
+
+    /// Sets bits in a PHY register.
+    pub fn set_bits(&mut self, regnum: u16, val: u16) -> Result {
+        self.modify(regnum, 0, val)
+    }
+
+    /// Clears bits in a PHY register.
+    pub fn clear_bits(&mut self, regnum: u16, val: u16) -> Result {
+        self.modify(regnum, val, 0)
+    }
+
     /// Resolves the advertisements into PHY settings.
     pub fn resolve_aneg_linkmode(&mut self) {
         let phydev = self.0.get();
-- 
2.43.0