/* * Copyright (C) 2012 Regents of the University of California * * This program is free software; you can redistribute it and/or * modify it under the terms of the GNU General Public License * as published by the Free Software Foundation, version 2. * * This program is distributed in the hope that it will be useful, * but WITHOUT ANY WARRANTY; without even the implied warranty of * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the * GNU General Public License for more details. */ #include #include #include #include /* * 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) { unsigned long ucycles = 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);