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/*
* 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 <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();
}
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);
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