linux-kernel - Re: [Stratos-dev] [PATCH V4 2/2] gpio: virtio: Add IRQ support

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Date:   Fri, 6 Aug 2021 10:00:42 +0200
From:   Arnd Bergmann <arnd@...nel.org>
To:     Viresh Kumar <viresh.kumar@...aro.org>
Cc:     "Michael S. Tsirkin" <mst@...hat.com>,
        Viresh Kumar <vireshk@...nel.org>,
        Linus Walleij <linus.walleij@...aro.org>,
        Cornelia Huck <cohuck@...hat.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "open list:DRM DRIVER FOR QEMU'S CIRRUS DEVICE" 
        <virtualization@...ts.linux-foundation.org>,
        Bartosz Golaszewski <bgolaszewski@...libre.com>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        "open list:GPIO SUBSYSTEM" <linux-gpio@...r.kernel.org>,
        Marc Zyngier <maz@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        "Enrico Weigelt, metux IT consult" <info@...ux.net>,
        Jason Wang <jasowang@...hat.com>,
        Stratos Mailing List <stratos-dev@...lists.linaro.org>
Subject: Re: [Stratos-dev] [PATCH V4 2/2] gpio: virtio: Add IRQ support

On Fri, Aug 6, 2021 at 9:44 AM Viresh Kumar via Stratos-dev
<stratos-dev@...lists.linaro.org> wrote:
>
> On 05-08-21, 15:10, Arnd Bergmann wrote:
> > I hope this can still be simplified by working out better which state
> > transitions are needed exactly. In particular, I would expect that we
> > can get away with not sending a VIRTIO_GPIO_MSG_IRQ_TYPE
> > for 'mask' state changes at all, but use that only for forcing 'enabled'
> > state changes.
>
> Something like this ?

> static void virtio_gpio_irq_mask(struct irq_data *d)
> {
>         /* Nothing to do here */
> }

You'd have to do /something/ here I think, if only setting the flag
that we don't want to deliver the next interrupt.

> static void virtio_gpio_irq_unmask(struct irq_data *d)
> {
>         struct gpio_chip *gc = irq_data_get_irq_chip_data(d);
>         struct virtio_gpio *vgpio = gpiochip_get_data(gc);
>
>         /* Queue the buffer unconditionally on unmask */
>         virtio_gpio_irq_prepare(vgpio, d->hwirq);
> }

And check the flag here to not requeue it if it's masked.

Now, there is already a flag in the irq descriptor, so rather than
having double accounting, the easy way may be to
just use irqd_irq_masked()/irq_state_set_masked(), or
have the irq core take care of this.

     Arnd