// 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;
|
u64 n;
|
|
if (unlikely(usecs > MAX_UDELAY_US)) {
|
n = (u64)usecs * riscv_timebase;
|
do_div(n, 1000000);
|
|
__delay(n);
|
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);
|
