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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Date:   Tue, 8 Dec 2020 15:04:50 +0100
From:   "Enrico Weigelt, metux IT consult" <lkml@...ux.net>
To:     Linus Walleij <linus.walleij@...aro.org>,
        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 08.12.20 10:38, Linus Walleij wrote:

Hi,

> 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.

Oh, thx.

It seems to implement a pseudo-irqchip driver. I've already though about
doing that, but didn't think its worth it, just for my driver alone.
I've implemented a few irq handling cb's directly the driver. But since
we already have it, I'll reconsider :)

BUT: this wasn't exactly my question :p

I've been looking for some more direct notification callback for gpio
consumers: here the consumer would register itself as a listener on
some gpio_desc and called back when something changes (with data what
exactly changed, eg. "gpio #3 input switched to high").

Seems we currently just have the indirect path via interrupts.

--mtx

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Enrico Weigelt, metux IT consult
Free software and Linux embedded engineering
info@...ux.net -- +49-151-27565287