linux-kernel - Re: [PATCH 1/5] dt-bindings: virtio: mmio: Add support for device subnode

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Date:   Wed, 14 Jul 2021 07:58:39 +0530
From:   Viresh Kumar <viresh.kumar@...aro.org>
To:     Arnd Bergmann <arnd@...nel.org>
Cc:     Jason Wang <jasowang@...hat.com>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Rob Herring <robh+dt@...nel.org>,
        Jean-Philippe Brucker <jean-philippe@...aro.org>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Bill Mills <bill.mills@...aro.org>,
        Alex Bennée <alex.bennee@...aro.org>,
        "Enrico Weigelt, metux IT consult" <info@...ux.net>,
        Jie Deng <jie.deng@...el.com>,
        DTML <devicetree@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        virtualization@...ts.linux-foundation.org
Subject: Re: [PATCH 1/5] dt-bindings: virtio: mmio: Add support for device
 subnode

On 13-07-21, 14:32, Arnd Bergmann wrote:
> On Tue, Jul 13, 2021 at 12:51 PM Viresh Kumar <viresh.kumar@...aro.org> wrote:
> 
> > +
> > +    virtio@...0 {
> > +        compatible = "virtio,mmio";
> > +        reg = <0x3200 0x100>;
> > +        interrupts = <43>;
> > +
> > +        #address-cells = <1>;
> > +        #size-cells = <0>;
> > +
> > +        i2c-virtio@0 {
> > +            reg = <VIRTIO_ID_I2C_ADAPTER>;
> > +        };
> > +    };
> 
> This works, but it seems oddly inconsistent with the way we do the same thing
> for PCI, USB and MMC devices that normally don't need device tree properties but
> can optionally have those.
> 
> All of the above use the "compatible" property to identify the device,
> rather than
> using the "reg" property. Neither of them is actually great here,
> since we already
> know what the device is and how to talk to it, but I'd still prefer doing this
> with
> 
>        compatible = "virtio,34";
> 
> or similar, where 34 is the numerical value of VIRTIO_ID_I2C_ADAPTER.
> This would then be required in the virtio-i2c binding.
> I think you can skip the #address-cells/#size-cells then.

That works, sure.

I think I misunderstood it when you said it earlier and thought that
you are asking to add compatible in the parent node itself and so did
it this way.

Though that may be the way we will end up doing it now :)

-- 
viresh