GPIO and IRQ Driver¶

A GPIO IRQ driver converts hardware edge events into software events. In this repo, GPIO interrupts were used as the foundation for event-driven character drivers, debounce logic, pollable drivers, and user-space notification models.

Basic Flow¶

GPIO input edge
        ↓
IRQ handler / threaded IRQ
        ↓
update driver state or event queue
        ↓
wake_up_interruptible()
        ↓
read() / poll() / epoll() in user space

IRQ Handler Design¶

A good IRQ design keeps the hard interrupt path short and defers heavier work to a safer context.

Common options:

Mechanism	Typical Use
Hard IRQ handler	Acknowledge event, capture minimal state
Threaded IRQ	Sleepable interrupt processing
Workqueue	Deferred processing outside interrupt context
Timer / delayed work	Debounce or delayed validation

Debounce Pattern¶

GPIO IRQ
    ↓
schedule delayed work
    ↓
read stable GPIO value
    ↓
push event into queue
    ↓
wake readers

Common Pitfalls¶

Warning

Do not sleep in a hard IRQ handler. Use a threaded IRQ, workqueue, or delayed work when the code may sleep.

Warning

An IRQ event should not be lost just because user space is not currently blocked in read(). Use driver state or an event queue.