spi_register_controller(9)

💅 spi_register_controller(9)

okay so bestie, welcome to the kernel API manual, this one's spi_register_controller(9) and it's literally the moment your SPI controller becomes ✨real✨.

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🌸 NAME 🌸

spi_register_controller — register SPI host or target controller

like, you built the thing, now introduce it to the bus 🫶

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✨ SYNOPSIS ✨

int spi_register_controller (struct spi_controller *ctlr );

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🎀 ARGUMENTS 🎀

• ctlr — the initialized controller. and when we say initialized we mean it — it originally came from spi_alloc_host or spi_alloc_target, no cap. don't just roll up with a random struct, it will not slay 💀

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🦋 CONTEXT 🦋

can sleep 😴

(translation: you're allowed to block in here, it's not one of Those functions)

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💖 DESCRIPTION 💖

SPI controllers don't just spawn into the SPI bus out of nowhere — they connect to their drivers using some other non-SPI bus, like the platform bus. so the final stage of probe in that code is where you call spi_register_controller, and that's what hooks you up to the SPI bus glue. iconic behavior honestly.

SPI controllers use board specific (often SOC specific) bus numbers, and board-specific addressing for SPI devices combines those numbers with chip select numbers. the way SPI works, it does not directly support dynamic device identification — so boards need configuration tables telling which chip is at which address. yes, an actual table. a whole little seating chart for your chips 🪑✨

This must be called from context that can sleep. fr fr, don't try this in atomic context.

⭐ after a successful return, the caller is responsible for calling spi_unregister_controller. that's you, bestie. it's your job now. don't ghost it 🙈

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🔥 RETURN 🔥

zero on success 🎉 else a negative error code 😭

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👑 SEE ALSO 👑

Kernel file ./drivers/spi/spi.c and its whole friend group:

• __spi_register_driver(9)
• spi_alloc_device(9)
• spi_add_device(9)
• spi_new_device(9)
• spi_unregister_device(9)
• spi_register_board_info(9)
• spi_res_alloc(9)
• spi_res_free(9)
• spi_res_add(9)
• spi_res_release(9)
• spi_finalize_current_transfer(9)
• __spi_pump_messages(9)
• spi_pump_messages(9)
• spi_take_timestamp_pre(9)
• spi_take_timestamp_post(9)
• spi_set_thread_rt(9)
• spi_get_next_queued_message(9)
• spi_finalize_current_message(9)
• spi_queued_transfer(9)
• spi_flush_queue(9)
• of_register_spi_devices(9)
• spi_new_ancillary_device(9)
• devm_spi_new_ancillary_device(9)
• acpi_spi_count_resources(9)
• acpi_spi_device_alloc(9)
• spi_target_abort(9)
• __spi_alloc_controller(9)
• __devm_spi_alloc_controller(9)
• spi_get_gpio_descs(9)
• devm_spi_register_controller(9)
• spi_unregister_controller(9)
• spi_replace_transfers(9)
• spi_split_transfers_maxsize(9)
• spi_split_transfers_maxwords(9)
• spi_set_cs_timing(9)
• spi_setup(9)
• spi_optimize_message(9)
• spi_unoptimize_message(9)
• devm_spi_optimize_message(9)
• spi_async(9)
• spi_sync(9)
• spi_sync_locked(9)
• spi_bus_lock(9)
• spi_bus_unlock(9)
• spi_write_then_read(9)

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🌈 and that's the whole page!! this little manual page lives in ./drivers/spi and it's dated October 2026 — so yeah, she's from the future, we stan a time traveler 💜🎀✨