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

[Arnd Bergmann]

On Wed, Dec 9, 2020 at 9:51 AM Linus Walleij <linus.walleij at linaro.org> wrote:
> On Tue, Dec 8, 2020 at 3:07 PM Enrico Weigelt, metux IT consult <lkml at metux.net> wrote:

> What we need to understand is if your new usecase is an outlier
> so it is simplest modeled by a "mock" irq_chip or we have to design
> something new altogether like notifications on changes. I suspect
> irq_chip would be best because all drivers using GPIOs for interrupts
> are expecting interrupts, and it would be an enormous task to
> change them all and really annoying to create a new mechanism
> on the side.

I would expect the platform abstraction to actually be close enough
to a chained irqchip that it actually works: the notification should
come in via vring_interrupt(), which is a normal interrupt handler
that calls vq->vq.callback(), calling generic_handle_irq() (and
possibly chained_irq_enter()/chained_irq_exit() around it) like the
other gpio drivers do should just work here I think, and if it did
not, then I would expect this to be just a bug in the driver rather
than something missing in the gpio framework.

       Arnd