1// SPDX-License-Identifier: GPL-2.0
2/*
3 * i8253 PIT clocksource
4 */
5#include <linux/clockchips.h>
6#include <linux/init.h>
7#include <linux/io.h>
8#include <linux/spinlock.h>
9#include <linux/timex.h>
10#include <linux/module.h>
11#include <linux/i8253.h>
12#include <linux/smp.h>
13
14/*
15 * Protects access to I/O ports
16 *
17 * 0040-0043 : timer0, i8253 / i8254
18 * 0061-0061 : NMI Control Register which contains two speaker control bits.
19 */
20DEFINE_RAW_SPINLOCK(i8253_lock);
21EXPORT_SYMBOL(i8253_lock);
22
23/*
24 * Handle PIT quirk in pit_shutdown() where zeroing the counter register
25 * restarts the PIT, negating the shutdown. On platforms with the quirk,
26 * platform specific code can set this to false.
27 */
28bool i8253_clear_counter_on_shutdown __ro_after_init = true;
29
30#ifdef CONFIG_CLKSRC_I8253
31/*
32 * Since the PIT overflows every tick, its not very useful
33 * to just read by itself. So use jiffies to emulate a free
34 * running counter:
35 */
36static u64 i8253_read(struct clocksource *cs)
37{
38 static int old_count;
39 static u32 old_jifs;
40 unsigned long flags;
41 int count;
42 u32 jifs;
43
44 raw_spin_lock_irqsave(&i8253_lock, flags);
45 /*
46 * Although our caller may have the read side of jiffies_lock,
47 * this is now a seqlock, and we are cheating in this routine
48 * by having side effects on state that we cannot undo if
49 * there is a collision on the seqlock and our caller has to
50 * retry. (Namely, old_jifs and old_count.) So we must treat
51 * jiffies as volatile despite the lock. We read jiffies
52 * before latching the timer count to guarantee that although
53 * the jiffies value might be older than the count (that is,
54 * the counter may underflow between the last point where
55 * jiffies was incremented and the point where we latch the
56 * count), it cannot be newer.
57 */
58 jifs = jiffies;
59 outb_p(0x00, PIT_MODE); /* latch the count ASAP */
60 count = inb_p(PIT_CH0); /* read the latched count */
61 count |= inb_p(PIT_CH0) << 8;
62
63 /* VIA686a test code... reset the latch if count > max + 1 */
64 if (count > PIT_LATCH) {
65 outb_p(0x34, PIT_MODE);
66 outb_p(PIT_LATCH & 0xff, PIT_CH0);
67 outb_p(PIT_LATCH >> 8, PIT_CH0);
68 count = PIT_LATCH - 1;
69 }
70
71 /*
72 * It's possible for count to appear to go the wrong way for a
73 * couple of reasons:
74 *
75 * 1. The timer counter underflows, but we haven't handled the
76 * resulting interrupt and incremented jiffies yet.
77 * 2. Hardware problem with the timer, not giving us continuous time,
78 * the counter does small "jumps" upwards on some Pentium systems,
79 * (see c't 95/10 page 335 for Neptun bug.)
80 *
81 * Previous attempts to handle these cases intelligently were
82 * buggy, so we just do the simple thing now.
83 */
84 if (count > old_count && jifs == old_jifs)
85 count = old_count;
86
87 old_count = count;
88 old_jifs = jifs;
89
90 raw_spin_unlock_irqrestore(&i8253_lock, flags);
91
92 count = (PIT_LATCH - 1) - count;
93
94 return (u64)(jifs * PIT_LATCH) + count;
95}
96
97static struct clocksource i8253_cs = {
98 .name = "pit",
99 .rating = 110,
100 .read = i8253_read,
101 .mask = CLOCKSOURCE_MASK(32),
102};
103
104int __init clocksource_i8253_init(void)
105{
106 return clocksource_register_hz(&i8253_cs, PIT_TICK_RATE);
107}
108#endif
109
110#ifdef CONFIG_CLKEVT_I8253
111static int pit_shutdown(struct clock_event_device *evt)
112{
113 if (!clockevent_state_oneshot(evt) && !clockevent_state_periodic(evt))
114 return 0;
115
116 raw_spin_lock(&i8253_lock);
117
118 outb_p(0x30, PIT_MODE);
119
120 if (i8253_clear_counter_on_shutdown) {
121 outb_p(0, PIT_CH0);
122 outb_p(0, PIT_CH0);
123 }
124
125 raw_spin_unlock(&i8253_lock);
126 return 0;
127}
128
129static int pit_set_oneshot(struct clock_event_device *evt)
130{
131 raw_spin_lock(&i8253_lock);
132 outb_p(0x38, PIT_MODE);
133 raw_spin_unlock(&i8253_lock);
134 return 0;
135}
136
137static int pit_set_periodic(struct clock_event_device *evt)
138{
139 raw_spin_lock(&i8253_lock);
140
141 /* binary, mode 2, LSB/MSB, ch 0 */
142 outb_p(0x34, PIT_MODE);
143 outb_p(PIT_LATCH & 0xff, PIT_CH0); /* LSB */
144 outb_p(PIT_LATCH >> 8, PIT_CH0); /* MSB */
145
146 raw_spin_unlock(&i8253_lock);
147 return 0;
148}
149
150/*
151 * Program the next event in oneshot mode
152 *
153 * Delta is given in PIT ticks
154 */
155static int pit_next_event(unsigned long delta, struct clock_event_device *evt)
156{
157 raw_spin_lock(&i8253_lock);
158 outb_p(delta & 0xff , PIT_CH0); /* LSB */
159 outb_p(delta >> 8 , PIT_CH0); /* MSB */
160 raw_spin_unlock(&i8253_lock);
161
162 return 0;
163}
164
165/*
166 * On UP the PIT can serve all of the possible timer functions. On SMP systems
167 * it can be solely used for the global tick.
168 */
169struct clock_event_device i8253_clockevent = {
170 .name = "pit",
171 .features = CLOCK_EVT_FEAT_PERIODIC,
172 .set_state_shutdown = pit_shutdown,
173 .set_state_periodic = pit_set_periodic,
174 .set_next_event = pit_next_event,
175};
176
177/*
178 * Initialize the conversion factor and the min/max deltas of the clock event
179 * structure and register the clock event source with the framework.
180 */
181void __init clockevent_i8253_init(bool oneshot)
182{
183 if (oneshot) {
184 i8253_clockevent.features |= CLOCK_EVT_FEAT_ONESHOT;
185 i8253_clockevent.set_state_oneshot = pit_set_oneshot;
186 }
187 /*
188 * Start pit with the boot cpu mask. x86 might make it global
189 * when it is used as broadcast device later.
190 */
191 i8253_clockevent.cpumask = cpumask_of(smp_processor_id());
192
193 clockevents_config_and_register(&i8253_clockevent, PIT_TICK_RATE,
194 0xF, 0x7FFF);
195}
196#endif
197