Load partially USB composite device

[loïc tourlonias]

On Wed, Aug 9, 2017 at 9:25 AM, Bjørn Mork <bjorn at mork.no> wrote:
> loïc tourlonias <loic.tourlonias at gmail.com> writes:

Thank's for the quick response

>
>> Hi everybody,
>>
>> In my project I have an USB composite device (a LTE modem) which use
>> USB to communicate with the processor. This device has several
>> interface to communicate but I do not use all of them. In particular,
>> it loads cdc_ether device which I don't use and I have an undesired
>> ethXX which interferes with a service in my system.
>
> Sounds like your system has other issues, but whatever...

I may not have been clear in my explanation. What seems wrong with my system?

>
>> To schematize, let's say my device is loaded on port 2 of usb1, I have
>> the following USB topology:
>> - 1-2:1.0: tty
>> - 1-2:1.1: tty
>> - 1-2:1.2: tty
>> - 1-2:1.3: tty
>> - 1-2:1.4: tty
>> - 1-2:1.5: eth (not desired)
>>
>> Is there a way to prevent this specific ethXX to mount?
>>
>> I've already tried to create a udev rules, but I don't manage to stop
>> the loading process.
>> Here is a summary of my tries:
>> 1/ I couldn't use the /sys/bus/usb1/.../1-2/activated file in my udev
>> rule because it's an USB composite device and I want to use the tty
>> interfaces but not the eth interface
>>
>> 2/ I have tried to stop the udev loading process, but setting MODALIAS
>> environment variable to a NULL-string doesn(t do the trick and
>> last-rule udev option has been removed in my udev version (1.8.2).
>>
>> 3/ I have tried to create a custom environment variable IGNORE_ETH and
>> modify my last rule which run modprobe with the modalias variable. In
>> the logs I see that modprobe isn't called by udev rules, but the
>> cdc_ether device is loaded all the same.
>>
>> 4/ I have think of creating a stub cdc_ether driver and use the
>> /etc/modprobe.d/my_file.conf to preempt the loading for my specific
>> usb composite device but this solution is ugly and I'm not sure it
>> will work.
>
> The cdc_ether driver treats any ID entry with .driver_info = 0 as a
> blacklist entry.  So you can dynamically blacklist devices by writing
> the "VID PID" to /sys/bus/usb/drivers/cdc_ether/new_id before the device
> is probed.
>
I have tried this and look at the source code of
driver/usb/core/driver.c. But I think this is not what I required.
What I understand is that the new_id file is used to dynamically add
new USB id to the cdc_ether driver.
What I want is the opposite, currently my device is loaded with
cdc_ether.ko and I want this device to remain unloaded.

Furthermore, after sending this email I have thought of renaming my
device in an udev rule. But unfortunately, it passed by an eth0 state
which I want to get rid of.

>
> Bjørn