gpiochip_add_data(9)

💅 gpiochip_add_data(9) — the Kernel API Manual, bestie edition 🎀

okay so this one is from the Kernel API Manual (yes, the 9 section, we love a kernel-dev moment) and it's literally the page about registering a gpio_chip. grab a strawberry drink 🍓, we're doing this.

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✨ SYNOPSIS ✨

gpiochip_add_data (gc , data );

that's it. two args. iconic.

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🫶 ARGUMENTS 🫶

• gc — the chip you're registering, and heads up: it needs gc->base already initialized before you hand it over. no showing up unprepared 💅
• data — the driver-private data that goes with this chip. it's giving "your stuff, your business" 🎀

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🌈 CONTEXT 🌈

potentially before irqs will work 😭 like, yes, it can happen that early. read the description, i'm begging you.

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👑 DESCRIPTION 👑

so here's the tea ☕. when gpiochip_add_data gets called very early during boot — like, early enough that GPIOs can be freely used — then the gc->parent device must be registered before the gpio framework's arch_initcall. otherwise sysfs initialization for GPIOs will fail rudely 💀 and nobody wants that energy in their dmesg.

also, gpiochip_add_data must only be called after gpiolib initialization — i.e. after core_initcall. that's the vibe check you cannot skip, fr fr.

and if gc->base is negative? that's the signal to request dynamic assignment of a range of valid GPIOs. you're not picking the number, the kernel is picking the number. main character energy only for the framework 🧚✨

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⭐ RETURN ⭐

• a negative errno if the chip can't be registered — for example because gc->base is invalid, or it's already associated with a different chip 🙈
• otherwise it returns zero as a success code. slay. that zero ate 💖

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🦋 SEE ALSO 🦋

• Kernel file ./include/linux/gpio/driver.h
• struct gpio_irq_chip(9)
• struct gpio_chip(9)
• for_each_hwgpio_in_range(9)
• for_each_hwgpio(9)
• for_each_requested_gpio_in_range(9)
• struct gpio_pin_range(9)

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and that's the whole page, no cap 💜 this one lives in ./include/linux/gpio, dated October 2026 — go read the source bestie, it's lowkey all there 🌸🫶