Re: Problems with Sierra LTE MC7710 Device

[Bjørn Mork <bjorn mork no>]

Harald Jung <support ecos de> writes:
> Am 17.01.2013 23:42, schrieb Bjørn Mork:
>> Great! Do you happen to know why the device was using configuration
>> #2 by default? That's unexpected. Recent versions of usb_modeswitch
>> will do that if it sessions a MBIM configuration, but only if you
>> have the cdc_mbim driver. So I don't think that can explain
>> this. Bjørn 
>
> I don't have an idea but I speculate that the usb controller on the
> fujitsu notebook could cause the problem.

I should have remembered this.  I've noticed it before.  But for anyone
else interested, the result is expected and not a bug anywhere.

>From the configuration selection routine in drivers/usb/core/generic.c:

                /* From the remaining configs, choose the first one whose
                 * first interface is for a non-vendor-specific class.
                 * Reason: Linux is more likely to have a class driver
                 * than a vendor-specific driver. */
                else if (udev->descriptor.bDeviceClass !=
                                                USB_CLASS_VENDOR_SPEC &&
                                (desc && desc->bInterfaceClass !=
                                                USB_CLASS_VENDOR_SPEC)) {
                        best = c;
                        break;
                }



So Linux intentionally selects the MBIM class configuration over the
vendor specific QMI configuration. That's probably worth being aware
of...

The reason this didn't hit the Huawei E367 is that it has a mass storage
class interface first in its QMI configuration (or really - legacy mode
switching configuration).  Hmm, can be somewhat confusing that the
default mode depends on whether the legacy mode uses USB storage mode
switching.


Bjørn