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