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: */
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
68void __udelay(unsigned long usecs)
69{
70	__cr16_delay(usecs * ((unsigned long)boot_cpu_data.cpu_hz / 1000000UL));
71}
72EXPORT_SYMBOL(__udelay);
73