__mdiobus_write(9)

📦 version 7.3.1, in nixpkgs unstable

🌸 __mdiobus_write — Kernel API Manual, bestie edition 🌸

okay so you're in the kernel API manual, section 9, and the star of the show is __mdiobus_write. hi bestie, let's get into it 💅

✨ NAME ✨

__mdiobus_write — the unlocked version of the mdiobus_write function. yes, the double underscore is doing main character work, it means "no lock, i trust you" 🫶

✨ SYNOPSIS ✨

int __mdiobus_write (struct mii_bus *bus , int addr , u32 regnum , u16
       val );

like look at that signature. iconic. no notes 💖

✨ ARGUMENTS ✨

  • bus — the mii_bus struct, aka the whole vibe of the bus you're talking to 🚌
  • addr — the phy address, so the kernel knows which phy we're having a moment with 👀
  • regnum — register number to write, like the little mailbox slot 📬
  • val — the value to write to regnum, the actual tea being delivered ☕

✨ RETURN ✨

Zero if successful — slay, zero means we ate 💅 — and a negative error code on failure 😭 (negative = the universe said no).

✨ DESCRIPTION ✨

so basically you're writing a MDIO bus register. that's the whole thing. but here's the catch and it's a big one, bestie: the caller must hold the mdio bus lock. 🔒

not "should". not "maybe". must. you're holding the lock, that's the deal. that's literally the entire reason this function exists separate from the locked one 💀

✨ NOTE ✨

MUST NOT be called from interrupt context.

say it with me: MUST NOT. interrupt context is not the vibe for this one, fr fr. do not do it. 🙈

✨ SEE ALSO ✨

Kernel file ./drivers/net/phy/mdio_bus.c — that's where the source lives if you wanna go read the raw material 📖

and the whole friend group, no cap, all of them:

okay that's the whole page, go forth and hold that lock 💜

this lil drop came out of ./drivers/net/phy and it's stamped October 2026 — mwah, see u in the next release 🎀✨

📦 where this page comes from