xref: /openbmc/linux/arch/arm/lib/delay.c (revision fa7f32422ea1ac276b45b96a540ed5981caaa61f)
1 /*
2  * Delay loops based on the OpenRISC implementation.
3  *
4  * Copyright (C) 2012 ARM Limited
5  *
6  * This program is free software; you can redistribute it and/or modify
7  * it under the terms of the GNU General Public License version 2 as
8  * published by the Free Software Foundation.
9  *
10  * This program is distributed in the hope that it will be useful,
11  * but WITHOUT ANY WARRANTY; without even the implied warranty of
12  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
13  * GNU General Public License for more details.
14  *
15  * You should have received a copy of the GNU General Public License
16  * along with this program; if not, write to the Free Software
17  * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
18  *
19  * Author: Will Deacon <will.deacon@arm.com>
20  */
21 
22 #include <linux/clocksource.h>
23 #include <linux/delay.h>
24 #include <linux/init.h>
25 #include <linux/kernel.h>
26 #include <linux/module.h>
27 #include <linux/export.h>
28 #include <linux/timex.h>
29 
30 /*
31  * Default to the loop-based delay implementation.
32  */
33 struct arm_delay_ops arm_delay_ops __ro_after_init = {
34 	.delay		= __loop_delay,
35 	.const_udelay	= __loop_const_udelay,
36 	.udelay		= __loop_udelay,
37 };
38 EXPORT_SYMBOL(arm_delay_ops);
39 
40 static const struct delay_timer *delay_timer;
41 static bool delay_calibrated;
42 static u64 delay_res;
43 
44 int read_current_timer(unsigned long *timer_val)
45 {
46 	if (!delay_timer)
47 		return -ENXIO;
48 
49 	*timer_val = delay_timer->read_current_timer();
50 	return 0;
51 }
52 EXPORT_SYMBOL_GPL(read_current_timer);
53 
54 static inline u64 cyc_to_ns(u64 cyc, u32 mult, u32 shift)
55 {
56 	return (cyc * mult) >> shift;
57 }
58 
59 static void __timer_delay(unsigned long cycles)
60 {
61 	cycles_t start = get_cycles();
62 
63 	while ((get_cycles() - start) < cycles)
64 		cpu_relax();
65 }
66 
67 static void __timer_const_udelay(unsigned long xloops)
68 {
69 	unsigned long long loops = xloops;
70 	loops *= arm_delay_ops.ticks_per_jiffy;
71 	__timer_delay(loops >> UDELAY_SHIFT);
72 }
73 
74 static void __timer_udelay(unsigned long usecs)
75 {
76 	__timer_const_udelay(usecs * UDELAY_MULT);
77 }
78 
79 void __init register_current_timer_delay(const struct delay_timer *timer)
80 {
81 	u32 new_mult, new_shift;
82 	u64 res;
83 
84 	clocks_calc_mult_shift(&new_mult, &new_shift, timer->freq,
85 			       NSEC_PER_SEC, 3600);
86 	res = cyc_to_ns(1ULL, new_mult, new_shift);
87 
88 	if (res > 1000) {
89 		pr_err("Ignoring delay timer %ps, which has insufficient resolution of %lluns\n",
90 			timer, res);
91 		return;
92 	}
93 
94 	if (!delay_calibrated && (!delay_res || (res < delay_res))) {
95 		pr_info("Switching to timer-based delay loop, resolution %lluns\n", res);
96 		delay_timer			= timer;
97 		lpj_fine			= timer->freq / HZ;
98 		delay_res			= res;
99 
100 		/* cpufreq may scale loops_per_jiffy, so keep a private copy */
101 		arm_delay_ops.ticks_per_jiffy	= lpj_fine;
102 		arm_delay_ops.delay		= __timer_delay;
103 		arm_delay_ops.const_udelay	= __timer_const_udelay;
104 		arm_delay_ops.udelay		= __timer_udelay;
105 	} else {
106 		pr_info("Ignoring duplicate/late registration of read_current_timer delay\n");
107 	}
108 }
109 
110 unsigned long calibrate_delay_is_known(void)
111 {
112 	delay_calibrated = true;
113 	return lpj_fine;
114 }
115 
116 void calibration_delay_done(void)
117 {
118 	delay_calibrated = true;
119 }
120