No #ifdef in .c files - example

After:
include/linux/hiddev.h
 #ifdef CONFIG_USB_HIDDEV
         extern void hiddev_hid_event (struct hid_device *, unsigned int usage,
                                           int value);
 #else
         static inline void hiddev_hid_event (struct hid_device *hid,
                                                   unsigned int usage, int value)
                                                  { }
 #endif

drivers/usb/hid_core.c
 static void hid_process_event (struct hid_device *hid, struct hid_field *field,
                                   struct hid_usage *usage, __s32 value)
 {
         hid_dump_input(usage, value); 
         if (hid->claimed & HID_CLAIMED_INPUT)
                 hidinput_hid_event(hid, field, usage, value);
         if (hid->claimed & HID_CLAIMED_HIDDEV)
                 hiddev_hid_event(hid, usage->hid, value);
 }