linux-kernel - Re: [PATCH V3 1/5] dt-bindings: virtio: Add binding for virtio devices

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Date:   Mon, 26 Jul 2021 23:20:13 +0200
From:   Arnd Bergmann <arnd@...nel.org>
To:     Rob Herring <robh+dt@...nel.org>
Cc:     Viresh Kumar <viresh.kumar@...aro.org>,
        Jason Wang <jasowang@...hat.com>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        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@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "open list:DRM DRIVER FOR QEMU'S CIRRUS DEVICE" 
        <virtualization@...ts.linux-foundation.org>
Subject: Re: [PATCH V3 1/5] dt-bindings: virtio: Add binding for virtio devices

On Mon, Jul 26, 2021 at 10:37 PM Rob Herring <robh+dt@...nel.org> wrote:
>
> On Mon, Jul 26, 2021 at 9:54 AM Arnd Bergmann <arnd@...nel.org> wrote:
> >
> > On Mon, Jul 26, 2021 at 4:57 PM Rob Herring <robh+dt@...nel.org> wrote:
> > > On Sun, Jul 25, 2021 at 10:52 PM Viresh Kumar <viresh.kumar@...aro.org> wrote:
> > > > +    description: |
> > > > +      Exactly one node describing the virtio device. The name of the node isn't
> > > > +      significant but its phandle can be used to by a user of the virtio device.
> > > > +
> > > > +  compatible:
> > > > +    pattern: "^virtio,[0-9a-f]+$"
> > >
> > > DID is only 4 chars? If so, "^virtio,[0-9a-f]{1,4}$"
> >
> > Any opinion on whether this should have any namespace prefix (or infix, I guess)
> > after "virtio,"?
> >
> > I previously suggested making it "virtio,device[0-9a-f]{1,4}$", which would
> > make it clearer that the following digits are the device ID rather
> > than something
> > else we might define in the future. Viresh picked this version because it's
> > somewhat more consistent with other subsystems.
>
> I'm fine either way, though I do find just a number a bit strange. So
> I'd lean toward adding 'device' or even just a 'd'.

I don't think just 'd' would be a good idea since it is indistinguishable from
a hexadecimal character. 'dev' would work though.

> BTW, what happens if/when the device protocol is rev'ed? A new DID or
> is there a separate revision that's discoverable?

This should normally be done using feature bits that are negotiated
between the two sides, and if only one side can do it, they use the
old revision.

There could be a new device ID but I don't think that has happened so far.

       Arnd