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

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Date:	Thu, 28 Aug 2008 13:35:57 -0700
From:	Greg KH <greg@...ah.com>
To:	Marcel Janssen <korgull@...e.nl>
Cc:	Marcel Janssen <marcel.janssen@...esy.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

On Thu, Aug 28, 2008 at 08:22:53PM +0200, Marcel Janssen wrote:
> On Thursday 28 August 2008 18:21:09 Greg KH wrote:
> > On Thu, Aug 28, 2008 at 11:37:24AM +0200, Marcel Janssen wrote:
> > > Hello Greg,
> > >
> > > I've got me a bit confused there :-)
> > >
> > > We currently only use the suspend/resume in our device which works on a
> > > received request from the PC.
> > > Basically sending suspend will make the device enter this mode. When the
> > > PC enters this mode, it's also clear it will send a resume when resuming
> > > from standby. But, how is this supposed to work when the PC is not in
> > > sleep mode.....how will the device wake up ?
> >
> > It should "automatically" wake up if something happens to it.  The USB
> > spec calls this out as to how this should work.  If the devices don't
> > support this, we don't have to add support for it :)
> 
> Actually this is a good point.
> 
> The USB spec mentions that the device should suspend when a constant idle 
> state is detected for more than 3.0ms.
> 
> 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.
> 
> Anyway, this is no issue for self-powered devices, which is probably the 
> majority in this class because most test & measurement devices need a good 
> power supply and USB just isn't fit for that unless you're able to make a 
> clean power from that (which is possible of course).
> Our device is both USB and self powered, but when in USB powered mode it will 
> only suspend when the host goes in sleep mode.
> 
> To be honest I would put suspend mode far down on the priority list :-)

Ok, thanks for letting us know, if they are self-powered, this shouldn't
be much of an issue.  Let's focus on getting the current driver working
again :)

thanks,

greg k-h
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