gpio_reg_init(9)

🦋 gpio_reg_init(9) 🦋

okay so this is a page from the Kernel API Manual, and the whole vibe is: you're turning one single fixed register into a whole lil gpio chip, and honestly? iconic. let's get into it bestie 💅

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✨ NAME ✨

gpio_reg_init — add a fixed in/out register as gpio

like literally, this is the function that says "hey, this register? it's a gpio now. periodt." 🎀

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✨ SYNOPSIS ✨

struct gpio_chip * gpio_reg_init (struct device *dev , void __iomem *reg
, int base , int num , const char *label , u32 direction , u32 def_out ,
const char *const *names , struct irq_domain *irqdom , const int *irqs
);

look at all those args, she's serving range 💀 but don't panic, we're going through every single one, fr fr.

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✨ ARGUMENTS ✨

• dev — optional struct device associated with this register. optional!! she doesn't need a device, she's independent like that 🦋
• reg — the original page literally just says -- undescribed -- and that's all we get, ngl 😭 no cap, whoever wrote this left it blank. moving on before it gets awkward 🙈
• base — start gpio number, or -1 to allocate. so you either hand her a starting number or you're like "girl, you pick" and -1 makes it allocate ✨
• num — number of GPIOs, maximum 32. that's the ceiling, bestie, 32 and not one more 👑
• label — GPIO chip label. her name tag at the party 🎀
• direction — bitmask of fixed direction, one per GPIO signal, 1 = in. so each signal gets its own bit and 1 means input, iykyk
• def_out — initial GPIO output value. the starting fit before she changes into anything else 💜
• names — array of num strings describing each GPIO signal, or NULL. one cute name per signal, or just NULL if you can't be bothered 🌸
• irqdom — irq domain or NULL. your interrupt domain, or NULL if there isn't one, lowkey simple
• irqs — array of num ints describing the interrupt mapping for each GPIO signal, or NULL. and here's the important bit: if irqdom is NULL, then this describes the Linux interrupt number; otherwise it describes the hardware interrupt number in the specified irq domain. two totally different meanings depending on irqdom, so don't mix them up bestie, I'm begging 😭🔥

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✨ DESCRIPTION ✨

okay so what this actually does: it adds a single-register GPIO device containing up to 32 GPIO signals, where each GPIO has a fixed input or output configuration. fixed! she's not out here being flexible, she's committed to her configuration and honestly same 💅

now the important caveats, and please read these because they're the whole vibe check:

• Only input GPIOs are assumed to be readable from the register — and only then after a double-read. double-read!! that's the rule, don't skip it or you'll be out here reading nonsense 💀
• Output values are assumed not to be readable. so don't go reading outputs expecting answers, she's not giving them 🙈

⚠️ these are assumptions the code makes, not suggestions — if you're counting on anything else, that's on you, bestie 😭

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✨ SEE ALSO ✨

• Kernel file ./drivers/gpio/gpio-reg.c — go read the source, that's where the real lore lives 📖✨

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and that's the whole page, you ate that 🫶

source: ./drivers/gpio 🌈 — dated October 2026, signed off as gpio_reg_init(9), and that's the tea girlie, mwah 💖🎀💅