phy_write(9)

🌸 phy_write(9) 🌸

okay bestie so this is a page straight out of the Kernel API Manual — the kernel's own little handbook — and it's all about one tiny but iconic function. Pull up a chair. 🫶

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✨ NAME ✨

phy_write — the convenience function for writing to a given PHY register. that's it, that's the whole vibe. it writes a value to a register. lowkey the whole point of the function.

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🎀 SYNOPSIS 🎀

int phy_write (struct phy_device *phydev , u32 regnum , u16 val );

three little arguments, one int coming back at you. she's compact. she's efficient. she ate.

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🦋 ARGUMENTS 🦋

• phydev — the phy_device struct. this is your main character — the device object you're doing the writing on.
• regnum — the register number to write. it's a u32, so pick your register and go 💅
• val — the value to write to regnum. it's a u16, and it's literally going into the register. girl's got a destination.

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💀 NOTE 💀

MUST NOT be called from interrupt context. not a suggestion, not a soft recommendation — MUST NOT. and the reason is so real: 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 out here waiting on an interrupt. 😭 do not do that to yourself.

periodt. no interrupt context. 🚫

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🌈 SEE ALSO 🌈

the kernel file this all lives in is ./include/linux/phy.h, and here's the whole extended friend group — every single one of them, no gatekeeping 💖

• the interface & clock girlies: enum phy_interface_t(9), phy_modes(9), rgmii_clock(9), enum link_inband_signalling(9), phy_interface_mode_is_rgmii(9), phy_interface_mode_is_8023z(9), phy_interface_is_rgmii(9)
• the bus & stats crew: struct mdio_bus_stats(9), struct mii_bus(9), mdiobus_alloc(9)
• the state & device squad: enum phy_state(9), struct phy_c45_device_ids(9), struct phy_oatc14_sqi_capability(9), struct phy_device(9), struct phy_driver(9), phy_module_driver(9)
• the diagnostics darlings: struct phy_tdr_config(9), struct phy_mse_capability(9), struct phy_mse_snapshot(9)
• the plca + led besties: struct phy_plca_cfg(9), struct phy_plca_status(9), struct phy_led(9)
• the id-comparison cuties: phy_id_compare(9), phy_id_compare_vendor(9), phy_id_compare_model(9), phydev_id_compare(9)
• the little status checks: phy_is_started(9), phy_driver_is_genphy(9), phy_disable_eee_mode(9), phy_can_wakeup(9), phy_may_wakeup(9), phy_is_pseudo_fixed_link(9), phy_on_sfp(9)
• the read/write & bit-twiddling icons: phy_read(9), __phy_read(9), __phy_write(9), __phy_modify_changed(9), phy_read_mmd_poll_timeout(9), __phy_set_bits(9), __phy_clear_bits(9), phy_set_bits(9), phy_clear_bits(9), __phy_set_bits_mmd(9), __phy_clear_bits_mmd(9), phy_set_bits_mmd(9), phy_clear_bits_mmd(9)
• the interrupt & timestamp gang: phy_interrupt_is_valid(9), phy_polling_mode(9), phy_has_hwtstamp(9), phy_has_rxtstamp(9), phy_has_tsinfo(9), phy_has_txtstamp(9), phy_is_default_hwtstamp(9)

go read all of them. i'll wait. 💜

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and that's the whole page, bestie!! this one shipped from ./include/linux and it's dated October 2026 — so yeah, future-dated kernel lore, we love to see it 👑✨ stay out of interrupt context and go write those registers responsibly 💅💖