spi_bitbang_start(9)

💅 spi_bitbang_start(9) 💅

okay so real talk, this is straight out of the Kernel API Manual and it's literally the glow-up moment for your polled/bitbanging SPI host controller driver. bestie, let's get into it ✨

---

🌸 NAME 🌸

spi_bitbang_start — start up a polled/bitbanging SPI host controller driver 🎀

---

⭐ SYNOPSIS ⭐

int spi_bitbang_start (struct spi_bitbang *bitbang );

---

🦋 ARGUMENTS 🦋

• bitbang — the driver handle, iykyk. this is your main character struct 💅

---

👑 DESCRIPTION 👑

okay so before you even think about calling this, the caller should have zero-initialized all parts of the structure, and then provided callbacks for chip selection and I/O loops. no cap, that's the bare minimum 🫶

if the host controller has a transfer method, its final step should call spi_bitbang_transfer — or, plot twist, that's the default if the transfer routine is not initialized. it should also set up the bus number and number of chipselects. don't forget those, fr fr 🙈

for i/o loops, provide callbacks either per-word (for bitbanging, or for hardware that basically exposes a shift register) or per-spi_transfer (which takes better advantage of hardware like fifos or DMA engines). pick your vibe, both are iconic 💖

drivers using per-word I/O loops should use (or call) spi_bitbang_setup, spi_bitbang_cleanup and spi_bitbang_setup_transfer to handle those SPI host controller methods. those methods are the defaults if the bitbang->txrx_bufs routine isn't initialized ✨

this routine registers the spi_controller, which will process requests in a dedicated task, keeping IRQs unblocked most of the time — highkey a serve 🔥. to stop processing those requests, call spi_bitbang_stop. that's the off switch, bestie 💀

🌈 little reminder: zero-init the struct, give it the callbacks, set the bus number and chipselect count, then hit start. skipping steps is not the vibe check you want to fail 🧚

---

💜 SEE ALSO 💜

Kernel file ./drivers/spi/spi-bitbang.c

---

and that's the whole thing, mwah 🍓 this lil' page lives in ./drivers/spi and it's dated October 2026 — go forth and bitbang responsibly, bestie 💅💖