Re: [RFC] usb: dwc2: hcd: fix split schedule issue

[Julius Werner]

> To handle things smarter, I think I need to research how to deal with
> hubs attached to hubs attached to hubs.  For instance:
>
> dwc2
> -> multi_tt hub
>     -> single_tt hub
>         -> device 1
>         -> device 2

Keep in mind that there's always at most one (active) TT between host
and device. The TT is the point where high-speed traffic is translated
to low-/full-speed traffic, so after that you cannot translate again.
With multiple hubs you either have

-> high-speed 2.0 hub (TT inactive / irrelevant for this path)
  -> multi or single TT 2.0 hub
    -> device

or

-> multi or single TT 2.0 hub
  -> full-speed 1.1 hub
     -> device

All the information you need should already be in struct usb_device.
If udev->tt->multi == 0, then it must be scheduled in the same group
as all other devices it shares udev->tt (the same pointer address)
with. If udev->tt->multi == 1, then it belongs in the same group as
all that have the same udev->tt and the same udev->ttport. There's
even a udev->tt->hcpriv where you could link a data structure (array)
in to keep track of these matching devices.

I agree that this is a nice-to-have optimization, though... it's more
important to get the thing stable, and I think it's fine to assume
that all low-/full-speed transfers go on the same bus for the first
iteration.
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/