linux-kernel - Re: [stable] A patch in 2.6.27.9 caused device names to change

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Date:	Wed, 4 Feb 2009 08:28:44 +0100
From:	Oliver Neukum <oliver@...kum.org>
To:	Greg KH <greg@...ah.com>
Cc:	Dan Williams <dcbw@...hat.com>, Chuck Ebbert <cebbert@...hat.com>,
	linux-kernel@...r.kernel.org, stable@...nel.org
Subject: Re: [stable]  A patch in 2.6.27.9 caused device names to change

Am Wednesday 04 February 2009 01:03:42 schrieb Greg KH:
> On Tue, Feb 03, 2009 at 09:50:11AM -0500, Dan Williams wrote:
 
> > For a long time we've been operating under the assumption that mobile
> > broadband devices should be driven by option and sierra, since those
> > drivers had the necessary buffering optimizations to support
> > higher-speed mobile broadband devices.
> 
> Who is "we" here?  Not me :)

We currently have three drivers that can handle high speed serial
connections in USB, option, sierra and cdc-acm.
 
> > That was true at least up until 2.6.24.
> 
> It all depends on the type of device.  If it says it is a cdc-acm modem,
> by all means, let that driver handle it, don't try to bind it to a
> different driver (that way lies races and madness...)
> 
> > Furthermore, up until this point, I have not seen mobile broadband
> > adapters (that aren't cellphones connected via USB) that *are* CDC-ACM
> > compliant.  Everything previously has advertised proprietary interfaces,
> > some of which are serial ports and some of which are not.
> 
> Probably because we never see those devices being reported, because they
> "just work" with no interaction from us.

As far as I can tell, devices implementing the class specification are
new and still quite rare. This is probably related to the relative newness
of the WHC specification.
  
> > Plus, are we expected to keep device names stable these days?  cdc-acm
> > is the catch-all driver, but if that driver is more "generic" and a
> > better driver is found, can we not update IDs just because the device
> > name may change?

There is no such thing as a better driver for a device that correctly
implements the class specification than the class driver. You haven't
seen complaints about cdc-acm's performance in a long time, have you?

	Regards
		Oliver
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