Hi Oleksij,

I love your patch! Yet something to improve:

[auto build test ERROR on net-next/master]

url:    https://github.com/0day-ci/linux/commits/Oleksij-Rempel/provide-generic-net-selftest-support/20210415-211011
base:   https://git.kernel.org/pub/scm/linux/kernel/git/davem/net-next.git 3a1aa533f7f676aad68f8dbbbba10b9502903770
config: sh-allmodconfig (attached as .config)
compiler: sh4-linux-gcc (GCC) 9.3.0
reproduce (this is a W=1 build):
        wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
        chmod +x ~/bin/make.cross
        # https://github.com/0day-ci/linux/commit/918b3886de4e3cbe278ddac71a69939b6a6abf80
        git remote add linux-review https://github.com/0day-ci/linux
        git fetch --no-tags linux-review Oleksij-Rempel/provide-generic-net-selftest-support/20210415-211011
        git checkout 918b3886de4e3cbe278ddac71a69939b6a6abf80
        # save the attached .config to linux build tree
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-9.3.0 make.cross W=1 ARCH=sh 

If you fix the issue, kindly add following tag as appropriate
Reported-by: kernel test robot <redacted>

All errors (new ones prefixed by >>):

   sh4-linux-ld: net/core/selftests.o: in function `net_selftest':

quoted

(.text+0x7d0): undefined reference to `phy_loopback'

Kconfig warnings: (for reference only)
   WARNING: unmet direct dependencies detected for SND_ATMEL_SOC_PDC
   Depends on SOUND && !UML && SND && SND_SOC && SND_ATMEL_SOC && HAS_DMA
   Selected by
   - SND_ATMEL_SOC_SSC && SOUND && !UML && SND && SND_SOC && SND_ATMEL_SOC
   - SND_ATMEL_SOC_SSC_PDC && SOUND && !UML && SND && SND_SOC && SND_ATMEL_SOC && ATMEL_SSC

---
0-DAY CI Kernel Test Service, Intel Corporation
https://lists.01.org/hyperkitty/list/kbuild-all@lists.01.org