Re: [PATCH v5 7/7] dt-bindings: usb: add documentation for aspeed usb-vhub

Tao Ren
2020-02-28T08:13:22Z

On Fri, Feb 28, 2020 at 02:02:28PM +1100, Benjamin Herrenschmidt wrote:
> On Thu, 2020-02-27 at 17:05 -0800, Tao Ren wrote:
> > > Also long run I think best is going to have a child node per downstream
> > > port, so we create a matching linux struct device. This will make it
> > > easier to deal with the other device-controller in the ast2600 which is
> > > basically one of these without a vhub above it.
> >
> > Maybe a dumb question: what would be the proper place to parse the child
> > node/properties when they are added? For example, in some usb_gadget_ops
> > callback?
>
> No. What the vhub would do is when it probes, it creates a platform
> device for each "port" child node that's linked to the DT node.
>
> The driver for the device then attaches to it via standard DT matching
> and checks if it has a vhub parent or not, and based on that, operates
> as a vhub child device or a standalone one.
>
> (For example, it might have different functions for EP selection since
> standalone devices have private EPs rather than a shared pool)
>
> They can both be in the same module or they can be separate modules
> with cross dependencies.
>
> Cheers,
> Ben.

I see. It's to describe these downstream devices (such as configurations
and according functions) in device tree, which is similar to defining a
composite device and linking functions/interfaces via configfs. Thanks for
the clarify.

Cheers,

Tao