Howto listen to/handle gpio state changes ? Re: [PATCH v2 2/2] drivers: gpio: add virtio-gpio guest driver

[Linus Walleij]

On Sat, Dec 5, 2020 at 9:15 PM Enrico Weigelt, metux IT consult
<lkml at metux.net> wrote:

> The virtio-gpio device/host can raise a signal on line state change.
> Kinda IRQ, but not actually running through real IRQs, instead by a
> message running though queue. (hmm, kida MSI ? :o).
>
> I've tried allocating an IRQ range and calling generic_handle_irq(),
> but then I'm getting unhanled IRQ trap.

This is Bartosz territory, but the gpio-mockup.c driver will insert
IRQs into the system, he went and added really core stuff
into kernel/irq to make this happen. Notice that in Kconfig
it does:

select IRQ_SIM

Then this is used:
include/linux/irq_sim.h

This is intended for simulating IRQs and both GPIO and IIO use it.
I think this inserts IRQs from debugfs and I have no idea how
flexible that is.

If it is suitable for what you want to do I don't know but it's
virtio so...

Yours,
Linus Walleij