linux-kernel - Re: [tip:x86/doc] x86/doc: mini-howto for using earlyprintk=dbgp

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Message-ID: <Pine.LNX.4.44L0.0903060958130.3461-100000@iolanthe.rowland.org>
Date:	Fri, 6 Mar 2009 10:52:00 -0500 (EST)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Daniel Walker <dwalker@...o99.com>
cc:	Randy Dunlap <randy.dunlap@...cle.com>,
	Yinghai Lu <yinghai@...nel.org>, <mingo@...hat.com>,
	<hpa@...or.com>, <linux-kernel@...r.kernel.org>,
	<ebiederm@...ssion.com>, <akpm@...ux-foundation.org>,
	<gregkh@...e.de>, <tglx@...utronix.de>, <sarah.a.sharp@...el.com>,
	<mingo@...e.hu>, <linux-tip-commits@...r.kernel.org>
Subject: Re: [tip:x86/doc] x86/doc: mini-howto for using earlyprintk=dbgp

On Thu, 5 Mar 2009, Daniel Walker wrote:

> On Thu, 2009-03-05 at 15:59 -0800, Randy Dunlap wrote:
> 
> > > - a.) Host/target system needs to have USB debug port capability.
> > > + a.) You will need two USB ports. One on the client/console system and one on 
> > > +     the target system.
> > > + 
> > > + b.) The client/console and target USB ports must have the debug port
> > > +     capability.
> > 
> > Is that correct on the (ugh, I think that the naming/terminology is
> > still mucked up, but you didn't do that) host/target system?
> > 
> > On the client/console (which I would call the host and I would call the
> > "Host/target" here just the Target system), a USB debug port is needed,
> > but on the Host/target, it should just look like a USB device.
> > At least that was the intent AFAIK/IIRC.  No?
> > 
> 
> >From the rest of document I assumed Host/target was referring to both
> sides of the connection. So you would need USB on both sides for this
> thing to work. I assumed Client/console was just the host. I guess that
> is all kind of confusing tho ..

The term "Host" is too confusing to be used here; it has too many other 
meanings.  "Target" is good.

"Client" is probably okay too, but I don't like "Console" so much
because both machines will have a console.  "Debugging console" is more
accurate but also more cumbersome.

> The document indicates you need this one capability on your USB port in
> addition to the USB device (check the complete document for how to find
> the capability). So both host and target need this one capability, and
> then you also need the USB device for the whole thing to work.

In fact the original document was rather clear about this; it says only
that the target machine needs the debug capability.  The client machine 
uses its normal USB driver and treats the debugging cable as a normal 
USB serial device.

Alan Stern

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