__phy_modify_mmd_changed(9)

📦 version 7.3.1, in nixpkgs unstable

💅 __phy_modify_mmd_changed(9) — from the Kernel API Manual, bestie 🎀

okay so picture this: you're deep in the kernel, you're in the Kernel API Manual, and you've stumbled onto __phy_modify_mmd_changed. Bestie. This is the unlocked little helper that lets you poke at a register inside an MMD ✨. Let's get into it, no cap.

🌸 NAME 🌸

__phy_modify_mmd_changed — the function for modifying a register on MMD. That's literally what it does, and it ate 💅

🦋 SYNOPSIS 🦋

int __phy_modify_mmd_changed (struct phy_device *phydev , int devad ,
u32 regnum , u16 mask , u16 set );

like yes, that's the whole signature, copy it exactly if you're typing it out, iykyk 🫶

🍓 ARGUMENTS 🍓

  • phydev — the phy_device struct, your main character of the hour 👑
  • devad — the MMD that's holding the register you wanna modify
  • regnum — the register number you're modifying, the actual address of the whole situation
  • mask — the bit mask of the bits you're clearing 🌈
  • set — the new value of the bits set in mask, which gets written to regnum

✨ DESCRIPTION ✨

So this is an unlocked helper function (yes, unlocked, as in it doesn't do the locking for you, keep that in mind bestie 🙈) and it lets you modify an MMD register like this:

new register value = (old register value & ~mask) | set

That's the whole vibe: mask off the bits you don't want, OR in the fresh ones, slay 💅

As for what you get back — it returns a negative errno, or 0 if there was literally no change, or 1 in case of a change. So yeah, that return value is doing a lil three-way thing and you should def check it fr fr 🔥

💜 SEE ALSO 💜

The kernel file lives at ./drivers/net/phy/phy-core.c, and honestly the whole friend group is here, go say hi 🫶:

and that's the whole page, bestie 💖 this lil legend comes from ./drivers/net/phy and the version is dated October 2026 — go forth and modify those MMD registers responsibly, mwah 🧚‍♀️💅

📦 where this page comes from