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SubjectRe: [PATCH v22 2/3] usb: misc: Add onboard_usb_hub driver
On Mon, Jun 27, 2022 at 02:54:03PM -0400, Alan Stern wrote:
> On Mon, Jun 27, 2022 at 11:14:47AM -0700, Matthias Kaehlcke wrote:
> > Maybe a bit more verbose documentation like this could help:
> >
> > Some background about the logic in this function, which can be a bit hard
> > to follow:
> >
> > Root hubs don't have dedicated device tree nodes, but use the node of their
> > HCD. The primary and secondary HCD are usually represented by a single DT
> > node. That means the root hubs of the primary and secondary HCD share the
> > same device tree node (the HCD node). As a result this function can be
> > called twice with the same DT node for root hubs. We only want to create a
> > single platform device for each physical onboard hub, hence for root hubs
> > the loop is only executed for the primary hub. Since the function scans
>
> By "primary hub", you mean "root hub for the primary HCD", right? This
> should be clarified.

Ok, thanks for the suggestion!

> > through all child nodes it still creates pdevs for onboard hubs connected
> > to the secondary hub if needed.
>
> And likewise for "secondary hub".
>
> >
> > Further there must be only one platform device for onboard hubs with a
> > companion hub (the hub is a single physical device). To achieve this two
>
> What do you mean by "companion hub"? I think you are using the wrong
> word here. If you're talking about the relation between the two logical
> hubs (one attached to the SuperSpeed bus and one attached to the
> Low/Full/High-speed bus) within a physical USB-3 hub, the correct term
> for this is "peer". See the existing usages in hub.h, hub.c, and
> port.c.
>
> "Companion" refers to something completely different (i.e., the UHCI or
> OHCI controllers that handle Low/Full-speed connections on behalf of a
> High-speed EHCI controller).

Yes it's the relation between the two logical hub. The term 'companion-hub'
stems from the binding and has been around since v6 of this series. I guess
we should update the binding if the terminology isn't correct.

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