Control and uses of USB for BMC's own internal uses

Ed Tanous ed at
Sun Dec 12 08:21:59 AEDT 2021

On Tue, Oct 19, 2021 at 6:46 AM Brad Bishop <bradleyb at> wrote:
> On Mon, 2021-10-18 at 13:32 -0700, Ed Tanous wrote:
> > On Mon, Oct 18, 2021 at 11:36 AM Bruce Mitchell
> > <bruce.mitchell at> wrote:
> > >
> > > On 10/17/2021 11:55, Bruce Mitchell wrote:
> > > >
> > > >
> >
> > Some clarifying questions:
> > There are physically available USB A ports connected directly to the
> > BMC on IBM platforms?  Or are these traces within the board?
> > What are these direct bmc usb ports used for normally?
> >
> > Considering that while the BMC use case is likely IBM specific,
> Just curious - what makes you say this?

I don't know of any BMCs that actually expose the BMC USB to a
physical port.  There are lots that expose the USB to the host via
internally routed lines.  Maybe there are more than just IBM boards
that I've not seen before?

> > but
> > the idea of disabling a generic USB port isn't IBM specific, it seems
> > like we need a model for a USB port on dbus and relate it to the
> > various resources.  If and when a host interface wanted to implement a
> > similar feature, we'd be able to reuse it.
> The goal isn't really to disable a USB port.  It is to disable the
> assorted bits of software that run when a USB device of a specific class
> (mass storage, serial, etc) is plugged into it.  What would it even mean
> to disable a USB port?  Would it need to be powered off?

I know there's use cases for disabling the USB ports entirely for
preventing things like USB booting.  Yes, ideally they wouldn't even
provide power to avoid things like shorting it out to take the server
down, but I don't know of any implementations that do that.


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