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

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Message-ID: <CAK8P3a3TabswETDAUec-2rbiNBk_K48-UdpTA5Ckvu5ogOyHjQ@mail.gmail.com>
Date:   Mon, 9 Aug 2021 09:55:07 +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 Mon, Aug 9, 2021 at 9:30 AM Viresh Kumar <viresh.kumar@...aro.org> wrote:
>
> On 06-08-21, 10:00, Arnd Bergmann wrote:
> > 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.
>
> I am not sure I understand why this would be required. If the
> interrupt is getting disabled, then unmask will not get called here
> and so we won't requeue anything. Same will happen with threaded
> handlers where the interrupt gets unmasked at a later point of time.

Ah, right. There is already a flag that gets checked by the caller.

It does feel odd to have an empty 'irq_mask' callback though, so
maybe there is still something missing, just not what I thought.

It's probably the result of calling handle_level_irq(), which as you
said is closer to what we want, but is not exactly what we need for
this protocol.

        Arnd