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