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

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Date:	Wed, 27 Aug 2008 14:58:08 -0400 (EDT)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Greg KH <greg@...ah.com>, Oliver Neukum <oliver@...kum.org>
cc:	USB list <linux-usb@...r.kernel.org>,
	Stefan Kopp <stefan_kopp@...lent.com>,
	Marcel Janssen <korgull@...e.nl>,
	Felipe Balbi <me@...ipebalbi.com>,
	Kernel development list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] USB: add USB test and measurement class driver - round
 2

On Wed, 27 Aug 2008, Greg KH wrote:

> On Wed, Aug 27, 2008 at 02:28:22PM -0400, Alan Stern wrote:
> > On Wed, 27 Aug 2008, Greg KH wrote:
> > 
> > > Here's an updated version of the usbtmc driver, with all of the
> > > different issues that have been raised, hopefully addressed.
> > 
> > This is an example of what I was discussing with Oliver.  In all 
> > likelihood you simply don't need usbtmc_mutex, and using it will cause 
> > a lockdep violation.
> > 
> > That's why so many of the other USB class drivers don't have an 
> > analogous static mutex.
> 
> Ok, then it's just safe to drop this static mutex entirely, right?

Yes, once you add the call to usb_deregister_dev.


On Wed, 27 Aug 2008, Oliver Neukum wrote:

> And this rule depends on sharing the USB major or not. This needs
> a big fat mention in Documentation.

You mean that the open/disconnect locking rule applies only to drivers 
that call usb_register_dev, i.e, drivers using the USB major.  Right?

I agree that it deserves to be mentioned in the documentation 
somewhere.  Where would be a good place?  None of the existing files in 
Documentation/usb seem appropriate.

Alan Stern

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