Re: Problems with Sierra LTE MC7710 Device

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;

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

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


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