linux-kernel - Re: [Stratos-dev] [PATCH V3 1/3] gpio: Add virtio-gpio driver

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Date:   Tue, 15 Jun 2021 09:30:09 +0200
From:   Vincent Guittot <vincent.guittot@...aro.org>
To:     Arnd Bergmann <arnd@...nel.org>
Cc:     Stefan Hajnoczi <stefanha@...hat.com>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Linus Walleij <linus.walleij@...aro.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        virtualization@...ts.linux-foundation.org,
        Bartosz Golaszewski <bgolaszewski@...libre.com>,
        "Stefano Garzarella --cc virtualization @ lists . linux-foundation . org" 
        <sgarzare@...hat.com>,
        "open list:GPIO SUBSYSTEM" <linux-gpio@...r.kernel.org>,
        Viresh Kumar <vireshk@...nel.org>,
        Stratos Mailing List <stratos-dev@...lists.linaro.org>,
        "Enrico Weigelt, metux IT consult" <info@...ux.net>,
        Jason Wang <jasowang@...hat.com>
Subject: Re: [Stratos-dev] [PATCH V3 1/3] gpio: Add virtio-gpio driver

On Mon, 14 Jun 2021 at 22:56, Arnd Bergmann <arnd@...nel.org> wrote:
>
> On Mon, Jun 14, 2021 at 3:24 PM Vincent Guittot
> <vincent.guittot@...aro.org> wrote:
> > On Mon, 14 Jun 2021 at 15:00, Arnd Bergmann <arnd@...nel.org> wrote:
> > > On Mon, Jun 14, 2021 at 2:50 PM Vincent Guittot via Stratos-dev <stratos-dev@...lists.linaro.org> wrote:>
> > >
> > > But this example seem to be completely different from the ones I mentioned:
> > > The scmi node that you have here looks like it shows up under the root of the
> > > device tree, not below the virtio device that implements the scmi transport.
> >
> > I was thinking of something like below:
> >
> >     deviceX: deviceX@...YYYY {
> >         ...
> >         gpio = <&virtio_gpio 0>;
> >         ...
> >     };
> >
> >     virtio_mmio@...0000 {
> >         dma-coherent;
> >         interrupts = <0x0 0x10 0x1>;
> >         reg = <0x0 0xa000000 0x0 0x200>;
> >         compatible = "virtio,mmio";
> >
> >         virtio_gpio: protocol@22 {
> >             reg = <0x22>;
> >         };
>
> Encoding the device ID as "reg" seems somewhat odd, especially since there
> can only be one child for each virtio device. The other bus types use the
> "compatible" property instead of "reg" for this purpose. This is still
> redundant,
> since the type is also known from the contents, but it seems less unusual.

At least this ensures to match directly the protocol id instead of
mapping a compatible string with the protocol id.

>
> The gpio node in the example is usually called "gpio" or "gpio-controller", and
> it would then need the "gpio-controller" and "#gpio-cells" properties so other
> nodes can refer to it by phandle.

yes, This short example is just to show what I mean.



>
>        Arnd