Re: [PATCH v4 04/10] dt-bindings: input: apple: Add DockChannel HID transport

[Rob Herring <robh@kernel.org>]

On Tue, Oct 06, 2026 at 08:09:47PM +0200, Yureka Lilian wrote:
> 
> On 10/6/26 18:00, Rob Herring wrote:
> > On Fri, Sep 25, 2026 at 10:09:31PM +1000, Michael Reeves wrote:
> > [...]
> > > +
> > > +  mboxes:
> > > +    items:
> > > +      - description: ASC mailbox used for RTKit control
> > > +      - description: DockChannel FIFO mailbox used for HID packets
> > > +
> > > +  mbox-names:
> > > +    items:
> > > +      - const: asc
> > > +      - const: dockchannel
> > > +
> > > +  iommus:
> > > +    maxItems: 1
> > > +
> > > +  stm:
> > > +    type: object
> > > +    description:
> > > +      STM interface providing the vendor, product and version identifiers
> > > +      and serial number shared by the HID devices. When present, the host
> > > +      must query this interface before registering the keyboard.
> > > +    additionalProperties: false
> > An empty node is unusual. Why can't you just query the STM interface and
> > treat it not existing or having those properties the same as no 'stm'
> > node.
> 
> The issue is there is no indicator for the stm *not* being present: We boot
> the MTP coprocessor, and then receive a message when the stm is available.
> In that case we know it's ready and we can proceed with obtaining the serial
> numbers and registering the hid devices. But if there is no stm, we simply
> do not get the stm ready message, and the hid devices are never registered
> (this is the case in the original downstream Asahi dockchannel-hid). To make
> the stm optional *without* taking the information from the device tree, this
> would require some sort of timeout for waiting for the stm ready message. I
> outlined the available options in this thread[1] and argued the empty stm
> subnode makes sense, since this is describing a peripheral which may or may
> not be present (and this information is useful to initialize the device
> properly).
> 
> Link[1]: https://lore.kernel.org/asahi/bbaca769-312c-4a24-9524-16cb2b4f277f@cyberchaos.dev/

Okay, but you don't need a node here. Just an 'apple,has-stm' or similar 
property will suffice.

Rob