linux-kernel - Re: [PATCH V6] gpio: virtio: Add IRQ support

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Date:   Thu, 21 Oct 2021 15:22:29 +0530
From:   Viresh Kumar <viresh.kumar@...aro.org>
To:     Andy Shevchenko <andy.shevchenko@...il.com>
Cc:     Arnd Bergmann <arnd@...nel.org>,
        Linus Walleij <linus.walleij@...aro.org>,
        Bartosz Golaszewski <bgolaszewski@...libre.com>,
        Bartosz Golaszewski <brgl@...ev.pl>,
        "Enrico Weigelt, metux IT consult" <info@...ux.net>,
        Viresh Kumar <vireshk@...nel.org>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Jason Wang <jasowang@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Jean-Philippe Brucker <jean-philippe@...aro.org>,
        Bill Mills <bill.mills@...aro.org>,
        Alex Bennée <alex.bennee@...aro.org>,
        Cornelia Huck <cohuck@...hat.com>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        "stratos-dev@...lists.linaro.org" <stratos-dev@...lists.linaro.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Marc Zyngier <maz@...nel.org>,
        "linux-gpio@...r.kernel.org" <linux-gpio@...r.kernel.org>,
        "virtualization@...ts.linux-foundation.org" 
        <virtualization@...ts.linux-foundation.org>
Subject: Re: [PATCH V6] gpio: virtio: Add IRQ support

On 21-10-21, 12:42, Andy Shevchenko wrote:
> On Thu, Oct 21, 2021 at 7:34 AM Viresh Kumar <viresh.kumar@...aro.org> wrote:
> > On 20-10-21, 18:10, Andy Shevchenko wrote:
> > > IIRC you add dead code. IRQ framework never calls this if type is not set.
> >
> > Yes, but it is allowed to call
> >
> > irq_set_irq_type(irq, IRQ_TYPE_NONE);
> >
> > and the irq framework won't disallow it AFAICT.
> 
> That's true, but how you may end up in this callback with a such?
> What the meaning of that call to the user?
 
I can see few calls like this in the kernel (mostly from irq-providers
only), but yeah sure I can drop it. We will error out if it ever gets
called and so can get it back later if required.
 
> > > >  struct virtio_gpio_config {
> > > >         __le16 ngpio;
> > > >         __u8 padding[2];
> > > > @@ -44,4 +56,17 @@ struct virtio_gpio_response_get_names {
> > > >         __u8 value[];
> > > >  };
> > > >
> > > > +/* Virtio GPIO IRQ Request / Response */
> > > > +struct virtio_gpio_irq_request {
> > > > +       __le16 gpio;
> > > > +};
> > > > +
> > > > +struct virtio_gpio_irq_response {
> > > > +       __u8 status;
> > > > +};
> > > >
> > > I’m wondering if those above should be packed.
> >
> > You are talking about the newly added ones or the ones before ?
> >
> > In any case, they are all already packed (i.e. they have explicit
> > padding wherever required) and properly aligned. Compiler won't add
> > any other padding to them.
> 
> Is it only for 64-bit to 64-bit communications?

That's what I have been looking at.

> If there is a possibility to have 32-bit to 64-bit or vice versa
> communication you have a problem.

This should work as well.

The structure will get aligned to the size of largest element and each
element will be aligned to itself. I don't see how this will break
even in case of 32/64 bit communication.

-- 
viresh