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From: Arnd Bergmann <arnd@kernel.org>
To: Viresh Kumar <viresh.kumar@linaro.org>
Cc: "Michael S. Tsirkin" <mst@redhat.com>,
	Viresh Kumar <vireshk@kernel.org>,
	Linus Walleij <linus.walleij@linaro.org>,
	Cornelia Huck <cohuck@redhat.com>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	"open list:DRM DRIVER FOR QEMU'S CIRRUS DEVICE" 
	<virtualization@lists.linux-foundation.org>,
	Bartosz Golaszewski <bgolaszewski@baylibre.com>,
	Geert Uytterhoeven <geert@linux-m68k.org>,
	"open list:GPIO SUBSYSTEM" <linux-gpio@vger.kernel.org>,
	Marc Zyngier <maz@kernel.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	Stratos Mailing List <stratos-dev@op-lists.linaro.org>,
	"Enrico Weigelt, metux IT consult" <info@metux.net>,
	Jason Wang <jasowang@redhat.com>
Subject: Re: [Stratos-dev] [PATCH V4 2/2] gpio: virtio: Add IRQ support
Date: Thu, 5 Aug 2021 15:10:21 +0200	[thread overview]
Message-ID: <CAK8P3a0kbmPLGCBrjAv7-dW=JWq-pdSBeGUHCxUFmMKvKhCg7w@mail.gmail.com> (raw)
In-Reply-To: <20210805124922.j7lts7tfmm4t2kpf@vireshk-i7>

On Thu, Aug 5, 2021 at 2:49 PM Viresh Kumar <viresh.kumar@linaro.org> wrote:
>
> On 05-08-21, 14:03, Arnd Bergmann wrote:
> > On Thu, Aug 5, 2021 at 1:26 PM Viresh Kumar via Stratos-dev
> > > Based on discussion we had today (offline), I changed the design a bit
> > > and used handle_level_irq() instead, as it provides consistent calls
> > > to mask/unmask(), which simplified the whole thing a bit.
> >
> > The new flow looks much nicer to me, without the workqueue, and
> > doing the requeue directly in the unmask() operation.
> >
> > I don't quite understand the purpose of the type_pending and
> > mask_pending flags yet, can you explain what they actually
> > do?
>
> They are required to make sure we don't send unnecessary
> VIRTIO_GPIO_MSG_IRQ_TYPE events to the device, every time bus_unlock()
> is called.
>
> mask_pending tracks if the masked state has changed since the time
> last bus_unlock() was called. So on an interrupt, both mask() and
> unmask() will get called by the irq-core now and mask_pending will
> change to true (in mask()} and then false (in unmask()). And
> eventually in bus_unlock() we won't send an extra
> VIRTIO_GPIO_MSG_IRQ_TYPE message.

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.

One part that I think is missing though is remembering the case
when an eventq message came in after an interrupt got masked
when the message was already armed. In this case, the
virtio_gpio_event_vq() function would not call the irq handler,
but the subsequent "unmask" callback would need to arrange
having it called.

        Arnd

  reply	other threads:[~2021-08-05 13:10 UTC|newest]

Thread overview: 18+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-08-03 11:36 [PATCH V4 0/2] gpio: Add virtio based driver Viresh Kumar
2021-08-03 11:36 ` [PATCH V4 1/2] gpio: Add virtio-gpio driver Viresh Kumar
2021-08-03 11:36 ` [PATCH V4 2/2] gpio: virtio: Add IRQ support Viresh Kumar
2021-08-03 15:01   ` Arnd Bergmann
2021-08-04  7:05     ` Viresh Kumar
2021-08-04  8:27       ` Arnd Bergmann
2021-08-05  7:05         ` Viresh Kumar
2021-08-05 11:26     ` Viresh Kumar
     [not found]     ` <0100017b1610f711-c53c79f2-9e28-4c45-bb42-8db09688b18e-000000@email.amazonses.com>
2021-08-05 12:03       ` [Stratos-dev] " Arnd Bergmann
2021-08-05 12:49         ` Viresh Kumar
2021-08-05 13:10           ` Arnd Bergmann [this message]
2021-08-06  7:44             ` Viresh Kumar
     [not found]             ` <0100017b1a6c0a05-e41dc16c-b326-4017-a63d-a24a6c1fde70-000000@email.amazonses.com>
2021-08-06  8:00               ` Arnd Bergmann
2021-08-09  7:30                 ` Viresh Kumar
2021-08-09  7:55                   ` Arnd Bergmann
2021-08-09 10:46                     ` Viresh Kumar
     [not found]                     ` <0100017b2a85eaf8-08b905fc-89f7-43a4-857e-070ca9691ce1-000000@email.amazonses.com>
2021-08-09 11:19                       ` Arnd Bergmann
2021-08-10  7:35                         ` Viresh Kumar

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