1/*
2 * This file is subject to the terms and conditions of the GNU General Public
3 * License. See the file "COPYING" in the main directory of this archive
4 * for more details.
5 *
6 * Copyright (C) 2007 by Ralf Baechle
7 */
8#include <linux/clocksource.h>
9#include <linux/cpufreq.h>
10#include <linux/init.h>
11#include <linux/sched_clock.h>
12
13#include <asm/time.h>
14
15static u64 c0_hpt_read(struct clocksource *cs)
16{
17 return read_c0_count();
18}
19
20static struct clocksource clocksource_mips = {
21 .name = "MIPS",
22 .read = c0_hpt_read,
23 .mask = CLOCKSOURCE_MASK(32),
24 .flags = CLOCK_SOURCE_IS_CONTINUOUS,
25};
26
27static u64 __maybe_unused notrace r4k_read_sched_clock(void)
28{
29 return read_c0_count();
30}
31
32static inline unsigned int rdhwr_count(void)
33{
34 unsigned int count;
35
36 __asm__ __volatile__(
37 " .set push\n"
38 " .set mips32r2\n"
39 " rdhwr %0, $2\n"
40 " .set pop\n"
41 : "=r" (count));
42
43 return count;
44}
45
46static bool rdhwr_count_usable(void)
47{
48 unsigned int prev, curr, i;
49
50 /*
51 * Older QEMUs have a broken implementation of RDHWR for the CP0 count
52 * which always returns a constant value. Try to identify this and don't
53 * use it in the VDSO if it is broken. This workaround can be removed
54 * once the fix has been in QEMU stable for a reasonable amount of time.
55 */
56 for (i = 0, prev = rdhwr_count(); i < 100; i++) {
57 curr = rdhwr_count();
58
59 if (curr != prev)
60 return true;
61
62 prev = curr;
63 }
64
65 pr_warn("Not using R4K clocksource in VDSO due to broken RDHWR\n");
66 return false;
67}
68
69#ifdef CONFIG_CPU_FREQ
70
71static bool __read_mostly r4k_clock_unstable;
72
73static void r4k_clocksource_unstable(char *reason)
74{
75 if (r4k_clock_unstable)
76 return;
77
78 r4k_clock_unstable = true;
79
80 pr_info("R4K timer is unstable due to %s\n", reason);
81
82 clocksource_mark_unstable(cs: &clocksource_mips);
83}
84
85static int r4k_cpufreq_callback(struct notifier_block *nb,
86 unsigned long val, void *data)
87{
88 if (val == CPUFREQ_POSTCHANGE)
89 r4k_clocksource_unstable(reason: "CPU frequency change");
90
91 return 0;
92}
93
94static struct notifier_block r4k_cpufreq_notifier = {
95 .notifier_call = r4k_cpufreq_callback,
96};
97
98static int __init r4k_register_cpufreq_notifier(void)
99{
100 return cpufreq_register_notifier(nb: &r4k_cpufreq_notifier,
101 CPUFREQ_TRANSITION_NOTIFIER);
102
103}
104core_initcall(r4k_register_cpufreq_notifier);
105
106#endif /* !CONFIG_CPU_FREQ */
107
108int __init init_r4k_clocksource(void)
109{
110 if (!cpu_has_counter || !mips_hpt_frequency)
111 return -ENXIO;
112
113 /* Calculate a somewhat reasonable rating value */
114 clocksource_mips.rating = 200 + mips_hpt_frequency / 10000000;
115
116 /*
117 * R2 onwards makes the count accessible to user mode so it can be used
118 * by the VDSO (HWREna is configured by configure_hwrena()).
119 */
120 if (cpu_has_mips_r2_r6 && rdhwr_count_usable())
121 clocksource_mips.vdso_clock_mode = VDSO_CLOCKMODE_R4K;
122
123 clocksource_register_hz(cs: &clocksource_mips, hz: mips_hpt_frequency);
124
125#ifndef CONFIG_CPU_FREQ
126 sched_clock_register(r4k_read_sched_clock, 32, mips_hpt_frequency);
127#endif
128
129 return 0;
130}
131

source code of linux/arch/mips/kernel/csrc-r4k.c