Hi Chunfeng,

FYI, the error/warning still remains.

tree:   https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master
head:   bdcf11de8f776152c82d2197b255c2d04603f976
commit: a66ada4f241c9a5a0bbabc5af511ea5dd4c2cbb8 usb: gadget: bcm63xx_udc: create debugfs directory under usb root
date:   10 months ago
config: mips-randconfig-p002-20200921 (attached as .config)
compiler: mips-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
        git checkout a66ada4f241c9a5a0bbabc5af511ea5dd4c2cbb8
        # save the attached .config to linux build tree
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-9.3.0 make.cross ARCH=mips 

If you fix the issue, kindly add following tag as appropriate
Reported-by: kernel test robot <lkp@intel.com>

All errors (new ones prefixed by >>):

   drivers/usb/gadget/udc/bcm63xx_udc.c: In function 'bcm63xx_udc_init_debugfs':
>> drivers/usb/gadget/udc/bcm63xx_udc.c:2251:46: error: 'usb_debug_root' undeclared (first use in this function)
    2251 |  root = debugfs_create_dir(udc->gadget.name, usb_debug_root);
         |                                              ^~~~~~~~~~~~~~
   drivers/usb/gadget/udc/bcm63xx_udc.c:2251:46: note: each undeclared identifier is reported only once for each function it appears in

# https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=a66ada4f241c9a5a0bbabc5af511ea5dd4c2cbb8
git remote add linus https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
git fetch --no-tags linus master
git checkout a66ada4f241c9a5a0bbabc5af511ea5dd4c2cbb8
vim +/usb_debug_root +2251 drivers/usb/gadget/udc/bcm63xx_udc.c

  2239	
  2240	/**
  2241	 * bcm63xx_udc_init_debugfs - Create debugfs entries.
  2242	 * @udc: Reference to the device controller.
  2243	 */
  2244	static void bcm63xx_udc_init_debugfs(struct bcm63xx_udc *udc)
  2245	{
  2246		struct dentry *root;
  2247	
  2248		if (!IS_ENABLED(CONFIG_USB_GADGET_DEBUG_FS))
  2249			return;
  2250	
> 2251		root = debugfs_create_dir(udc->gadget.name, usb_debug_root);
  2252		udc->debugfs_root = root;
  2253	
  2254		debugfs_create_file("usbd", 0400, root, udc, &bcm63xx_usbd_dbg_fops);
  2255		debugfs_create_file("iudma", 0400, root, udc, &bcm63xx_iudma_dbg_fops);
  2256	}
  2257	

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