| // SPDX-License-Identifier: GPL-2.0-only |
| /* |
| * Copyright (C) 2012 Regents of the University of California |
| */ |
| |
| #include <linux/delay.h> |
| #include <linux/param.h> |
| #include <linux/timex.h> |
| #include <linux/export.h> |
| |
| /* |
| * This is copies from arch/arm/include/asm/delay.h |
| * |
| * 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_US 2000 |
| #define MAX_UDELAY_HZ 1000 |
| #define UDELAY_MULT (2147UL * HZ + 483648UL * HZ / 1000000UL) |
| #define UDELAY_SHIFT 31 |
| |
| #if HZ > MAX_UDELAY_HZ |
| #error "HZ > MAX_UDELAY_HZ" |
| #endif |
| |
| /* |
| * RISC-V supports both UDELAY and NDELAY. This is largely the same as above, |
| * but with different constants. I added 10 bits to the shift to get this, but |
| * the result is that I need a 64-bit multiply, which is slow on 32-bit |
| * platforms. |
| * |
| * NDELAY_MULT = 2^41 * HZ / 1000000000 |
| * = (2^41 / 1000000000) * HZ |
| * = 2199.02325555 * HZ |
| * = 2199 * HZ + 23255550 * HZ / 1000000000 |
| * |
| * The maximum here is to avoid 64-bit overflow, but it isn't checked as it |
| * won't happen. |
| */ |
| #define MAX_NDELAY_NS (1ULL << 42) |
| #define MAX_NDELAY_HZ MAX_UDELAY_HZ |
| #define NDELAY_MULT ((unsigned long long)(2199ULL * HZ + 23255550ULL * HZ / 1000000000ULL)) |
| #define NDELAY_SHIFT 41 |
| |
| #if HZ > MAX_NDELAY_HZ |
| #error "HZ > MAX_NDELAY_HZ" |
| #endif |
| |
| void __delay(unsigned long cycles) |
| { |
| u64 t0 = get_cycles(); |
| |
| while ((unsigned long)(get_cycles() - t0) < cycles) |
| cpu_relax(); |
| } |
| EXPORT_SYMBOL(__delay); |
| |
| void udelay(unsigned long usecs) |
| { |
| u64 ucycles = (u64)usecs * lpj_fine * UDELAY_MULT; |
| |
| if (unlikely(usecs > MAX_UDELAY_US)) { |
| __delay((u64)usecs * riscv_timebase / 1000000ULL); |
| return; |
| } |
| |
| __delay(ucycles >> UDELAY_SHIFT); |
| } |
| EXPORT_SYMBOL(udelay); |
| |
| void ndelay(unsigned long nsecs) |
| { |
| /* |
| * This doesn't bother checking for overflow, as it won't happen (it's |
| * an hour) of delay. |
| */ |
| unsigned long long ncycles = nsecs * lpj_fine * NDELAY_MULT; |
| __delay(ncycles >> NDELAY_SHIFT); |
| } |
| EXPORT_SYMBOL(ndelay); |