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-generic/types.h> 21 #include <asm/param.h> /* HZ */ 22 23 extern unsigned long loops_per_jiffy; 24 25 static inline void __delay(unsigned long loops) 26 { 27 __asm__ __volatile__( 28 " mov lp_count, %0 \n" 29 " lp 1f \n" 30 " nop \n" 31 "1: \n" 32 : 33 : "r"(loops) 34 : "lp_count"); 35 } 36 37 extern void __bad_udelay(void); 38 39 /* 40 * Normal Math for computing loops in "N" usecs 41 * -we have precomputed @loops_per_jiffy 42 * -1 sec has HZ jiffies 43 * loops per "N" usecs = ((loops_per_jiffy * HZ / 1000000) * N) 44 * 45 * Approximate Division by multiplication: 46 * -Mathematically if we multiply and divide a number by same value the 47 * result remains unchanged: In this case, we use 2^32 48 * -> (loops_per_N_usec * 2^32 ) / 2^32 49 * -> (((loops_per_jiffy * HZ / 1000000) * N) * 2^32) / 2^32 50 * -> (loops_per_jiffy * HZ * N * 4295) / 2^32 51 * 52 * -Divide by 2^32 is very simply right shift by 32 53 * -We simply need to ensure that the multiply per above eqn happens in 54 * 64-bit precision (if CPU doesn't support it - gcc can emaulate it) 55 */ 56 57 static inline void __udelay(unsigned long usecs) 58 { 59 unsigned long loops; 60 61 /* (u64) cast ensures 64 bit MPY - real or emulated 62 * HZ * 4295 is pre-evaluated by gcc - hence only 2 mpy ops 63 */ 64 loops = ((u64) usecs * 4295 * HZ * loops_per_jiffy) >> 32; 65 66 __delay(loops); 67 } 68 69 #define udelay(n) (__builtin_constant_p(n) ? ((n) > 20000 ? __bad_udelay() \ 70 : __udelay(n)) : __udelay(n)) 71 72 #endif /* __ASM_ARC_UDELAY_H */ 73