linux-kernel - Re: Fwd: Re: [PATCH] USB: add USB test and measurement class driver

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Message-Id: <200808281537.50952.david-b@pacbell.net>
Date:	Thu, 28 Aug 2008 15:37:50 -0700
From:	David Brownell <david-b@...bell.net>
To:	Greg KH <greg@...ah.com>, Marcel Janssen <marcel.janssen@...esy.nl>
Cc:	Marcel Janssen <korgull@...e.nl>,
	Stefan Kopp <stefan_kopp@...lent.com>,
	Felipe Balbi <me@...ipebalbi.com>, linux-usb@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: Fwd: Re: [PATCH] USB: add USB test and measurement class driver

> > I either have not seen that happening before or I missed something when 
> > writing my firmware. I'll keep an eye on my USB analyzer though :-)
> > Although it's a good thing to keep to the spec, I also believe that in the 
> > case of a test and measurement device suspending the device may be an 
> > unwanted behaviour but perhaps I do misinterpret this part of the spec here.

For the record, the "gadgetfs" interface was originally developed with
userspace USB TMC implementations in mind.  I don't recall whether that
effort got out of the lab though.

The issue of suspend/resume explicitly came up.  The scenario which
stuck in my mind was that when the TMC device was in USB-level suspend
state, the code on the peripheral would need to know about that so
it could re-enable manual controls.  The host could no longer be
issuing commands.  (Some of these folk were on the TMC design team.)

One of the customers didn't seem to like the notion of not being able
to turn off stress tests on a $US 20,000 engine ... and watching the
device(s) under test blow up.  Accidental destruction == bad, it seems!

So I think you probably do misinterpret the spec.  That issue was not
only discussed, but proper handling for it was identified.

- Dave
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