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

Oliver Neukum
2009-02-04T07:57:46Z

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