Re: [PATCH net,stable] qmi_wwan: do not steal interfaces from class drivers

From: Bjørn Mork <bjorn@mork.no>
Date: Wed,  2 May 2018 22:22:54 +0200

The USB_DEVICE_INTERFACE_NUMBER matching macro assumes that
the { vendorid, productid, interfacenumber } set uniquely
identifies one specific function.  This has proven to fail
for some configurable devices. One example is the Quectel
EM06/EP06 where the same interface number can be either
QMI or MBIM, without the device ID changing either.

Fix by requiring the vendor-specific class for interface number
based matching.  Functions of other classes can and should use
class based matching instead.

Fixes: 03304bcb5ec4 ("net: qmi_wwan: use fixed interface number matching")
Signed-off-by: Bjørn Mork <bjorn@mork.no>
---
It's quite possible that the fix should be integrated in the
USB_DEVICE_INTERFACE_NUMBER macro instead.  But that has grown a few
other users since it was added, so changing it now seems risky. 
Another option is of course adding a new match macro with the
USB_CLASS_VENDOR_SPEC match integrated. Maybe best?

But I'm proposing this as-is for now, since this quickfix seems most
suitable for stable backporting.

Yes, this simpler approache is better for net and -stable.

Applied.

If you want to do something more sophisticated, that can be done
in net-next.

Thanks.