in include/asm/io.h [47:53]
static inline void ctrl_bclr(int b, void __iomem *addr) { if (__builtin_constant_p(b)) __asm__("bclr %1,%0" : "+WU"(*(u8 *)addr): "i"(b)); else __asm__("bclr %w1,%0" : "+WU"(*(u8 *)addr): "r"(b)); }