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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 }