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Diffstat (limited to 'arch/arm/include/asm/delay.h')
-rw-r--r-- | arch/arm/include/asm/delay.h | 100 |
1 files changed, 100 insertions, 0 deletions
diff --git a/arch/arm/include/asm/delay.h b/arch/arm/include/asm/delay.h new file mode 100644 index 0000000000..1d069e558d --- /dev/null +++ b/arch/arm/include/asm/delay.h @@ -0,0 +1,100 @@ +/* SPDX-License-Identifier: GPL-2.0 */ +/* + * Copyright (C) 1995-2004 Russell King + * + * Delay routines, using a pre-computed "loops_per_second" value. + */ +#ifndef __ASM_ARM_DELAY_H +#define __ASM_ARM_DELAY_H + +#include <asm/page.h> +#include <asm/param.h> /* HZ */ + +/* + * Loop (or tick) based delay: + * + * loops = loops_per_jiffy * jiffies_per_sec * delay_us / us_per_sec + * + * where: + * + * jiffies_per_sec = HZ + * us_per_sec = 1000000 + * + * Therefore the constant part is HZ / 1000000 which is a small + * fractional number. To make this usable with integer math, we + * scale up this constant by 2^31, perform the actual multiplication, + * and scale the result back down by 2^31 with a simple shift: + * + * loops = (loops_per_jiffy * delay_us * UDELAY_MULT) >> 31 + * + * where: + * + * UDELAY_MULT = 2^31 * HZ / 1000000 + * = (2^31 / 1000000) * HZ + * = 2147.483648 * HZ + * = 2147 * HZ + 483648 * HZ / 1000000 + * + * 31 is the biggest scale shift value that won't overflow 32 bits for + * delay_us * UDELAY_MULT assuming HZ <= 1000 and delay_us <= 2000. + */ +#define MAX_UDELAY_MS 2 +#define UDELAY_MULT UL(2147 * HZ + 483648 * HZ / 1000000) +#define UDELAY_SHIFT 31 + +#ifndef __ASSEMBLY__ + +struct delay_timer { + unsigned long (*read_current_timer)(void); + unsigned long freq; +}; + +extern struct arm_delay_ops { + void (*delay)(unsigned long); + void (*const_udelay)(unsigned long); + void (*udelay)(unsigned long); + unsigned long ticks_per_jiffy; +} arm_delay_ops; + +#define __delay(n) arm_delay_ops.delay(n) + +/* + * This function intentionally does not exist; if you see references to + * it, it means that you're calling udelay() with an out of range value. + * + * With currently imposed limits, this means that we support a max delay + * of 2000us. Further limits: HZ<=1000 + */ +extern void __bad_udelay(void); + +/* + * division by multiplication: you don't have to worry about + * loss of precision. + * + * Use only for very small delays ( < 2 msec). Should probably use a + * lookup table, really, as the multiplications take much too long with + * short delays. This is a "reasonable" implementation, though (and the + * first constant multiplications gets optimized away if the delay is + * a constant) + */ +#define __udelay(n) arm_delay_ops.udelay(n) +#define __const_udelay(n) arm_delay_ops.const_udelay(n) + +#define udelay(n) \ + (__builtin_constant_p(n) ? \ + ((n) > (MAX_UDELAY_MS * 1000) ? __bad_udelay() : \ + __const_udelay((n) * UDELAY_MULT)) : \ + __udelay(n)) + +/* Loop-based definitions for assembly code. */ +extern void __loop_delay(unsigned long loops); +extern void __loop_udelay(unsigned long usecs); +extern void __loop_const_udelay(unsigned long); + +/* Delay-loop timer registration. */ +#define ARCH_HAS_READ_CURRENT_TIMER +extern void register_current_timer_delay(const struct delay_timer *timer); + +#endif /* __ASSEMBLY__ */ + +#endif /* defined(_ARM_DELAY_H) */ + |