1/* SPDX-License-Identifier: GPL-2.0-only */ 2/* 3 * Copyright (C) 2004, 2007-2010, 2011-2012 Synopsys, Inc. (www.synopsys.com) 4 * 5 * Delay routines using pre computed loops_per_jiffy value. 6 * 7 * vineetg: Feb 2012 8 * -Rewrote in "C" to avoid dealing with availability of H/w MPY 9 * -Also reduced the num of MPY operations from 3 to 2 10 * 11 * Amit Bhor: Codito Technologies 2004 12 */ 13 14#ifndef __ASM_ARC_UDELAY_H 15#define __ASM_ARC_UDELAY_H 16 17#include <asm-generic/types.h> 18#include <asm/param.h> /* HZ */ 19 20extern unsigned long loops_per_jiffy; 21 22static inline void __delay(unsigned long loops) 23{ 24 __asm__ __volatile__( 25 " mov lp_count, %0 \n" 26 " lp 1f \n" 27 " nop \n" 28 "1: \n" 29 : 30 : "r"(loops) 31 : "lp_count"); 32} 33 34extern void __bad_udelay(void); 35 36/* 37 * Normal Math for computing loops in "N" usecs 38 * -we have precomputed @loops_per_jiffy 39 * -1 sec has HZ jiffies 40 * loops per "N" usecs = ((loops_per_jiffy * HZ / 1000000) * N) 41 * 42 * Approximate Division by multiplication: 43 * -Mathematically if we multiply and divide a number by same value the 44 * result remains unchanged: In this case, we use 2^32 45 * -> (loops_per_N_usec * 2^32 ) / 2^32 46 * -> (((loops_per_jiffy * HZ / 1000000) * N) * 2^32) / 2^32 47 * -> (loops_per_jiffy * HZ * N * 4295) / 2^32 48 * 49 * -Divide by 2^32 is very simply right shift by 32 50 * -We simply need to ensure that the multiply per above eqn happens in 51 * 64-bit precision (if CPU doesn't support it - gcc can emaulate it) 52 */ 53 54static inline void __udelay(unsigned long usecs) 55{ 56 unsigned long loops; 57 58 /* (u64) cast ensures 64 bit MPY - real or emulated 59 * HZ * 4295 is pre-evaluated by gcc - hence only 2 mpy ops 60 */ 61 loops = ((u64) usecs * 4295 * HZ * loops_per_jiffy) >> 32; 62 63 __delay(loops); 64} 65 66#define udelay(n) (__builtin_constant_p(n) ? ((n) > 20000 ? __bad_udelay() \ 67 : __udelay(n)) : __udelay(n)) 68 69#endif /* __ASM_ARC_UDELAY_H */ 70