[mirror_ubuntu-artful-kernel.git] / arch / arc / include / asm / delay.h

/*
 * 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__(
	"	mov lp_count, %0	\n"
	"	lp  1f			\n"
	"	nop			\n"
	"1:				\n"
	: : "r"(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 */
Commit	Line	Data
d8005e6b VG	1	/*
	2	* Copyright (C) 2004, 2007-2010, 2011-2012 Synopsys, Inc. (www.synopsys.com)
	3	*
	4	* This program is free software; you can redistribute it and/or modify
	5	* it under the terms of the GNU General Public License version 2 as
	6	* published by the Free Software Foundation.
	7	*
	8	* Delay routines using pre computed loops_per_jiffy value.
	9	*
	10	* vineetg: Feb 2012
	11	* -Rewrote in "C" to avoid dealing with availability of H/w MPY
	12	* -Also reduced the num of MPY operations from 3 to 2
	13	*
	14	* Amit Bhor: Codito Technologies 2004
	15	*/
	16
	17	#ifndef __ASM_ARC_UDELAY_H
	18	#define __ASM_ARC_UDELAY_H
	19
	20	#include <asm/param.h> /* HZ */
	21
	22	static inline void __delay(unsigned long loops)
	23	{
	24	__asm__ __volatile__(
6f3a172f VG	25	" mov lp_count, %0 \n"
	26	" lp 1f \n"
	27	" nop \n"
	28	"1: \n"
	29	: : "r"(loops));
d8005e6b VG	30	}
	31
	32	extern void __bad_udelay(void);
	33
	34	/*
	35	* Normal Math for computing loops in "N" usecs
	36	* -we have precomputed @loops_per_jiffy
	37	* -1 sec has HZ jiffies
	38	* loops per "N" usecs = ((loops_per_jiffy * HZ / 1000000) * N)
	39	*
	40	* Approximate Division by multiplication:
	41	* -Mathematically if we multiply and divide a number by same value the
	42	* result remains unchanged: In this case, we use 2^32
	43	* -> (loops_per_N_usec * 2^32 ) / 2^32
	44	* -> (((loops_per_jiffy * HZ / 1000000) * N) * 2^32) / 2^32
	45	* -> (loops_per_jiffy * HZ * N * 4295) / 2^32
	46	*
	47	* -Divide by 2^32 is very simply right shift by 32
	48	* -We simply need to ensure that the multiply per above eqn happens in
	49	* 64-bit precision (if CPU doesn't support it - gcc can emaulate it)
	50	*/
	51
	52	static inline void __udelay(unsigned long usecs)
	53	{
	54	unsigned long loops;
	55
7efd0da2	56	/* (u64) cast ensures 64 bit MPY - real or emulated
d8005e6b VG	57	* HZ * 4295 is pre-evaluated by gcc - hence only 2 mpy ops
d8005e6b VG	58	*/
7efd0da2	59	loops = ((u64) usecs * 4295 * HZ * loops_per_jiffy) >> 32;
d8005e6b VG	60
	61	__delay(loops);
	62	}
	63
	64	#define udelay(n) (__builtin_constant_p(n) ? ((n) > 20000 ? __bad_udelay() \
	65	: __udelay(n)) : __udelay(n))
	66
	67	#endif /* __ASM_ARC_UDELAY_H */