1 // SPDX-License-Identifier: GPL-2.0 2 /* 3 * Precise Delay Loops for parisc 4 * 5 * based on code by: 6 * Copyright (C) 1993 Linus Torvalds 7 * Copyright (C) 1997 Martin Mares <mj@atrey.karlin.mff.cuni.cz> 8 * Copyright (C) 2008 Jiri Hladky <hladky _dot_ jiri _at_ gmail _dot_ com> 9 * 10 * parisc implementation: 11 * Copyright (C) 2013 Helge Deller <deller@gmx.de> 12 */ 13 14 15 #include <linux/module.h> 16 #include <linux/preempt.h> 17 #include <linux/init.h> 18 19 #include <asm/delay.h> 20 #include <asm/special_insns.h> /* for mfctl() */ 21 #include <asm/processor.h> /* for boot_cpu_data */ 22 23 /* CR16 based delay: */ __cr16_delay(unsigned long __loops)24static void __cr16_delay(unsigned long __loops) 25 { 26 /* 27 * Note: Due to unsigned math, cr16 rollovers shouldn't be 28 * a problem here. However, on 32 bit, we need to make sure 29 * we don't pass in too big a value. The current default 30 * value of MAX_UDELAY_MS should help prevent this. 31 */ 32 u32 bclock, now, loops = __loops; 33 int cpu; 34 35 preempt_disable(); 36 cpu = smp_processor_id(); 37 bclock = mfctl(16); 38 for (;;) { 39 now = mfctl(16); 40 if ((now - bclock) >= loops) 41 break; 42 43 /* Allow RT tasks to run */ 44 preempt_enable(); 45 asm volatile(" nop\n"); 46 barrier(); 47 preempt_disable(); 48 49 /* 50 * It is possible that we moved to another CPU, and 51 * since CR16's are per-cpu we need to calculate 52 * that. The delay must guarantee that we wait "at 53 * least" the amount of time. Being moved to another 54 * CPU could make the wait longer but we just need to 55 * make sure we waited long enough. Rebalance the 56 * counter for this CPU. 57 */ 58 if (unlikely(cpu != smp_processor_id())) { 59 loops -= (now - bclock); 60 cpu = smp_processor_id(); 61 bclock = mfctl(16); 62 } 63 } 64 preempt_enable(); 65 } 66 67 __udelay(unsigned long usecs)68void __udelay(unsigned long usecs) 69 { 70 __cr16_delay(usecs * ((unsigned long)boot_cpu_data.cpu_hz / 1000000UL)); 71 } 72 EXPORT_SYMBOL(__udelay); 73