in include/asm/io.h [55:61]
static inline void ctrl_bset(int b, void __iomem *addr) { if (__builtin_constant_p(b)) __asm__("bset %1,%0" : "+WU"(*(u8 *)addr): "i"(b)); else __asm__("bset %w1,%0" : "+WU"(*(u8 *)addr): "r"(b)); }