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

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Message-ID: <CACRpkdb4R4yHcUV2KbGEC_RkU+QmH6Xg7X+qee8sEa9TURGr8A@mail.gmail.com>
Date:   Tue, 8 Dec 2020 10:38:43 +0100
From:   Linus Walleij <linus.walleij@...aro.org>
To:     "Enrico Weigelt, metux IT consult" <lkml@...ux.net>,
        Bartosz Golaszewski <bgolaszewski@...libre.com>
Cc:     "Enrico Weigelt, metux IT consult" <info@...ux.net>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Jonathan Corbet <corbet@....net>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Jason Wang <jasowang@...hat.com>,
        Linux Doc Mailing List <linux-doc@...r.kernel.org>,
        "open list:GPIO SUBSYSTEM" <linux-gpio@...r.kernel.org>,
        virtualization@...ts.linux-foundation.org,
        linux-riscv@...ts.infradead.org
Subject: Re: Howto listen to/handle gpio state changes ? Re: [PATCH v2 2/2]
 drivers: gpio: add virtio-gpio guest driver

On Sat, Dec 5, 2020 at 9:15 PM Enrico Weigelt, metux IT consult
<lkml@...ux.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