[coreboot] USB HUB depth

Joshua Pincus joshua.pincus at gmail.com
Thu Mar 9 18:53:11 CET 2017

Hi Nico,

Thanks for your email.

Indeed, I'm talking about libpayload's USB stack.  There does seem to be a
limit as I don't see usbhub.c or generic_hub.c calling any routines beyond
enable_port() for the ports beyond the HUB.  Enable_port() merely provides
power to those ports.  It doesn't scan them and then attach them in any way.


On Thu, Mar 9, 2017 at 5:16 AM, Nico Huber <nico.huber at secunet.com> wrote:

> On 09.03.2017 11:18, Joshua Pincus wrote:
> > Hi,
> >
> > I'm new to coreboot and to this group.  As this is my first post, let me
> > thank you folks for developing an impressive and incredibly useful
> product!
> Hi Joshua,
> > I recently fired up the coreboot USB stack on an x86 development board.
> > The USB stack reported back that I have 2 EHCI host controllers on the
> > board.  Each controller, in turn, has a number of ports.  Attached to at
> > most 1 of the ports beyond each controller is a USB 2.0 hub.  Each hub,
> in
> > turn, has a number of ports which the coreboot USB stack enables.
> are you talking about libpayload's USB stack? coreboot itself doesn't
> have one.
> >
> > My issue is this: I see the host controllers get initialized.  I see the
> > aforementioned hubs get initialized.  I see the ports underneath those
> hubs
> > get enabled.  I do not see nor can I find any existing code that scans
> and
> > attaches the ports associated with those hubs.  Consequently, none of the
> > devices (aka keyboard, USB stick, etc.) plugged into the ports beyond
> those
> > hubs are scanned and attached.  Put another way, it looks like the USB
> > stack, as currently written, only scans and attaches devices at tier 0
> and
> > tier 1.  Anything beyond the hub is merely enabled.
> >
> > Am I wrong or missing something?  How difficult would it be to continue
> the
> > process of recursion to subsequent tiers?
> If you are talking about libpayload, there shouldn't be an artificial
> limit. Responsible for hub class USB devices is the code in drivers/usb/
> generic_hub.c + drivers/usb/usbhub.c.
> Hope that helps,
> Nico
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