linux/include/asm-generic/delay.h

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#ifndef __ASM_GENERIC_DELAY_H
#define __ASM_GENERIC_DELAY_H
/* Undefined functions to get compile-time errors */
extern void __bad_udelay(void);
extern void __bad_ndelay(void);
extern void __udelay(unsigned long usecs);
extern void __ndelay(unsigned long nsecs);
extern void __const_udelay(unsigned long xloops);
extern void __delay(unsigned long loops);
/*
* The weird n/20000 thing suppresses a "comparison is always false due to
* limited range of data type" warning with non-const 8-bit arguments.
*/
/* 0x10c7 is 2**32 / 1000000 (rounded up) */
#define udelay(n) \
({ \
if (__builtin_constant_p(n)) { \
if ((n) / 20000 >= 1) \
__bad_udelay(); \
else \
__const_udelay((n) * 0x10c7ul); \
} else { \
__udelay(n); \
} \
})
/* 0x5 is 2**32 / 1000000000 (rounded up) */
#define ndelay(n) \
({ \
if (__builtin_constant_p(n)) { \
if ((n) / 20000 >= 1) \
__bad_ndelay(); \
else \
__const_udelay((n) * 5ul); \
} else { \
__ndelay(n); \
} \
})
#endif /* __ASM_GENERIC_DELAY_H */