1 /* SPDX-License-Identifier: GPL-2.0 */ 2 #ifndef __ASM_GENERIC_DELAY_H 3 #define __ASM_GENERIC_DELAY_H 4 5 #include <linux/math.h> 6 #include <vdso/time64.h> 7 8 /* Undefined functions to get compile-time errors */ 9 extern void __bad_udelay(void); 10 extern void __bad_ndelay(void); 11 12 extern void __udelay(unsigned long usecs); 13 extern void __ndelay(unsigned long nsecs); 14 extern void __const_udelay(unsigned long xloops); 15 extern void __delay(unsigned long loops); 16 17 /* 18 * The microseconds/nanosecond delay multiplicators are used to convert a 19 * constant microseconds/nanoseconds value to a value which can be used by the 20 * architectures specific implementation to transform it into loops. 21 */ 22 #define UDELAY_CONST_MULT ((unsigned long)DIV_ROUND_UP(1ULL << 32, USEC_PER_SEC)) 23 #define NDELAY_CONST_MULT ((unsigned long)DIV_ROUND_UP(1ULL << 32, NSEC_PER_SEC)) 24 25 /* 26 * The maximum constant udelay/ndelay value picked out of thin air to prevent 27 * too long constant udelays/ndelays. 28 */ 29 #define DELAY_CONST_MAX 20000 30 31 /** 32 * udelay - Inserting a delay based on microseconds with busy waiting 33 * @usec: requested delay in microseconds 34 * 35 * When delaying in an atomic context ndelay(), udelay() and mdelay() are the 36 * only valid variants of delaying/sleeping to go with. 37 * 38 * When inserting delays in non atomic context which are shorter than the time 39 * which is required to queue e.g. an hrtimer and to enter then the scheduler, 40 * it is also valuable to use udelay(). But it is not simple to specify a 41 * generic threshold for this which will fit for all systems. An approximation 42 * is a threshold for all delays up to 10 microseconds. 43 * 44 * When having a delay which is larger than the architecture specific 45 * %MAX_UDELAY_MS value, please make sure mdelay() is used. Otherwise a overflow 46 * risk is given. 47 * 48 * Please note that ndelay(), udelay() and mdelay() may return early for several 49 * reasons (https://lists.openwall.net/linux-kernel/2011/01/09/56): 50 * 51 * #. computed loops_per_jiffy too low (due to the time taken to execute the 52 * timer interrupt.) 53 * #. cache behaviour affecting the time it takes to execute the loop function. 54 * #. CPU clock rate changes. 55 */ 56 static __always_inline void udelay(unsigned long usec) 57 { 58 if (__builtin_constant_p(usec)) { 59 if (usec >= DELAY_CONST_MAX) 60 __bad_udelay(); 61 else 62 __const_udelay(usec * UDELAY_CONST_MULT); 63 } else { 64 __udelay(usec); 65 } 66 } 67 68 /** 69 * ndelay - Inserting a delay based on nanoseconds with busy waiting 70 * @nsec: requested delay in nanoseconds 71 * 72 * See udelay() for basic information about ndelay() and it's variants. 73 */ 74 static __always_inline void ndelay(unsigned long nsec) 75 { 76 if (__builtin_constant_p(nsec)) { 77 if (nsec >= DELAY_CONST_MAX) 78 __bad_ndelay(); 79 else 80 __const_udelay(nsec * NDELAY_CONST_MULT); 81 } else { 82 __ndelay(nsec); 83 } 84 } 85 #define ndelay(x) ndelay(x) 86 87 #endif /* __ASM_GENERIC_DELAY_H */ 88