mdiobus_c45_read_nested(9)

📦 version 7.3.1, in nixpkgs unstable

💖 mdiobus_c45_read_nested — like, the NESTED version of mdiobus_c45_read ✨

okay bestie, so this is straight out of the Kernel API Manual and it's genuinely so much less scary than the name makes it look 🫶 the name is mdiobus_c45_read_nested, and yes the (9) is part of the whole vibe, iykyk 💅

✨ SYNOPSIS ✨

int mdiobus_c45_read_nested (struct mii_bus *bus , int addr , int devad
, u32 regnum );

like… literally that's the whole signature, no cap 🎀

🦋 ARGUMENTS 🦋

  • bus — the mii_bus struct, bestie. that's your bus babe 🌸
  • addr — the phy address, the little address of your phy ✨
  • devad — device address to read 👑 (yes, c45 things get a device address, iconic)
  • regnum — register number to read 💜

🌈 RETURN 🌈

so if everything slays, you get the register value back 🎀 and if it doesn't? you get a negative error code on failure 😭 that's it, that's the contract, fr fr.

🔥 DESCRIPTION 🔥

okay so the whole point of this one: when you've got nested MDIO bus access, you use mutex_lock_nested so you avoid lockdep false positives ✨ that's literally the description, no extra lore, that's the tea 💅

like lockdep was out here being dramatic and this function said "not today" 💀

💀 NOTE 💀

MUST NOT be called from interrupt context 🚨 and this is a hard MUST, not a soft little suggestion bestie!! the reason: the bus read/write functions may wait for an interrupt to conclude the operation — so if you're already in interrupt context you'd be waiting on yourself, which is giving main character energy in the worst way 😭🙈 don't do it!!

🎀 SEE ALSO 🎀

all the siblings and cousins, in the kernel file ./drivers/net/phy/mdio_bus.c:

💖 okay that's the whole page bestie, go forth and read your c45 registers safely 💖

signing off from ./drivers/net/phy, dated October 2026, brought to you by the one and only mdiobus_c45_read_nested(9) 🌸🫶✨

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