mirror of https://gitee.com/openkylin/linux.git
67 lines
1.9 KiB
C
67 lines
1.9 KiB
C
/*
|
|
* Copyright (C) 2004, 2007-2010, 2011-2012 Synopsys, Inc. (www.synopsys.com)
|
|
*
|
|
* This program is free software; you can redistribute it and/or modify
|
|
* it under the terms of the GNU General Public License version 2 as
|
|
* published by the Free Software Foundation.
|
|
*
|
|
* Delay routines using pre computed loops_per_jiffy value.
|
|
*
|
|
* vineetg: Feb 2012
|
|
* -Rewrote in "C" to avoid dealing with availability of H/w MPY
|
|
* -Also reduced the num of MPY operations from 3 to 2
|
|
*
|
|
* Amit Bhor: Codito Technologies 2004
|
|
*/
|
|
|
|
#ifndef __ASM_ARC_UDELAY_H
|
|
#define __ASM_ARC_UDELAY_H
|
|
|
|
#include <asm/param.h> /* HZ */
|
|
|
|
static inline void __delay(unsigned long loops)
|
|
{
|
|
__asm__ __volatile__(
|
|
" lp 1f \n"
|
|
" nop \n"
|
|
"1: \n"
|
|
: "+l"(loops));
|
|
}
|
|
|
|
extern void __bad_udelay(void);
|
|
|
|
/*
|
|
* Normal Math for computing loops in "N" usecs
|
|
* -we have precomputed @loops_per_jiffy
|
|
* -1 sec has HZ jiffies
|
|
* loops per "N" usecs = ((loops_per_jiffy * HZ / 1000000) * N)
|
|
*
|
|
* Approximate Division by multiplication:
|
|
* -Mathematically if we multiply and divide a number by same value the
|
|
* result remains unchanged: In this case, we use 2^32
|
|
* -> (loops_per_N_usec * 2^32 ) / 2^32
|
|
* -> (((loops_per_jiffy * HZ / 1000000) * N) * 2^32) / 2^32
|
|
* -> (loops_per_jiffy * HZ * N * 4295) / 2^32
|
|
*
|
|
* -Divide by 2^32 is very simply right shift by 32
|
|
* -We simply need to ensure that the multiply per above eqn happens in
|
|
* 64-bit precision (if CPU doesn't support it - gcc can emaulate it)
|
|
*/
|
|
|
|
static inline void __udelay(unsigned long usecs)
|
|
{
|
|
unsigned long loops;
|
|
|
|
/* (u64) cast ensures 64 bit MPY - real or emulated
|
|
* HZ * 4295 is pre-evaluated by gcc - hence only 2 mpy ops
|
|
*/
|
|
loops = ((u64) usecs * 4295 * HZ * loops_per_jiffy) >> 32;
|
|
|
|
__delay(loops);
|
|
}
|
|
|
|
#define udelay(n) (__builtin_constant_p(n) ? ((n) > 20000 ? __bad_udelay() \
|
|
: __udelay(n)) : __udelay(n))
|
|
|
|
#endif /* __ASM_ARC_UDELAY_H */
|