Android Kernel - Unable to activate CONFIG_USB_ETH=y in the kernel dot config - linux

Question

I am trying to configure Android Kernel (msm-4.4)to have USB-CDC Ethernet Support in order to implement USB tethering in the low level. What I want to do is to migrate what's done in the following link to Android: https://developer.ridgerun.com/wiki/index.php/How_to_use_USB_device_networking
The following are already enabled in the .config:
CONFIG_USB=y
CONFIG_SND_USB=y
CONFIG_USB_SUPPORT=y
CONFIG_USB_GADGET=y
CONFIG_USB_CONFIGFS_UEVENT=y
However, when I add the following
CONFIG_USB_ETH=y
CONFIG_USB_ETH_EEM=y
Resulting .config has CONFIG_USB_CONFIGFS_UEVENT disabled:
CONFIG_USB_ETH=y
# CONFIG_USB_CONFIGFS_UEVENT is not set
which results in kernel compilation errors:
In function 'gadgets_make':
error: 'gadget_index' undeclared (first use in this function)
gadget_index++;
^
note: each undeclared identifier is reported only once for each function it appears in
In function 'gadgets_drop':
error: 'struct gadget_info' has no member named 'dev'
if (gi->dev) {
^
When I try to compile CONFIG_USB_ETH as a module, kernel compilation succeeds, but the resulting .config don't have it as enabled:
# CONFIG_USB_ETH is not set
I want to understand why something bizarre like this happens. I searched through the entire Android source code and couldn't find which triggers this blocking behavior.
Please have a look at the following Kconfigs if you require:
https://github.com/android-linux-stable/msm-4.4/blob/5a05099fd7feedfa07a75720669caf5f374810d4/drivers/usb/gadget/legacy/Kconfig
https://github.com/android-linux-stable/msm-4.4/blob/5a05099fd7feedfa07a75720669caf5f374810d4/drivers/usb/gadget/legacy/Kconfig
Any guidance to identify this problem is much appreciated.

Answer 1

You should use CONFIG_USB_NET_CDC_EEM=y instead of CONFIG_USB_ETH=y.
CONFIG_USB_ETH is not compatible with CONFIG_USB_CONFIGFS_UEVENT