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From:   Linus Walleij <linus.walleij@linaro.org>
Date:   Tue, 8 Dec 2020 10:38:43 +0100
Message-ID: <CACRpkdb4R4yHcUV2KbGEC_RkU+QmH6Xg7X+qee8sEa9TURGr8A@mail.gmail.com>
Subject: Re: Howto listen to/handle gpio state changes ? Re: [PATCH v2 2/2]
 drivers: gpio: add virtio-gpio guest driver
To:     "Enrico Weigelt, metux IT consult" <lkml@metux.net>,
        Bartosz Golaszewski <bgolaszewski@baylibre.com>
Cc:     "Enrico Weigelt, metux IT consult" <info@metux.net>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Jonathan Corbet <corbet@lwn.net>,
        "Michael S. Tsirkin" <mst@redhat.com>,
        Jason Wang <jasowang@redhat.com>,
        Linux Doc Mailing List <linux-doc@vger.kernel.org>,
        "open list:GPIO SUBSYSTEM" <linux-gpio@vger.kernel.org>,
        virtualization@lists.linux-foundation.org,
        linux-riscv@lists.infradead.org
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On Sat, Dec 5, 2020 at 9:15 PM Enrico Weigelt, metux IT consult
<lkml@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