Line data Source code
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 : */
20 : DEFINE_RAW_SPINLOCK(i8253_lock);
21 : EXPORT_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 : */
28 : bool 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 : */
36 : static 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 :
97 : static struct clocksource i8253_cs = {
98 : .name = "pit",
99 : .rating = 110,
100 : .read = i8253_read,
101 : .mask = CLOCKSOURCE_MASK(32),
102 : };
103 :
104 : int __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
111 0 : static int pit_shutdown(struct clock_event_device *evt)
112 : {
113 0 : if (!clockevent_state_oneshot(evt) && !clockevent_state_periodic(evt))
114 : return 0;
115 :
116 0 : raw_spin_lock(&i8253_lock);
117 :
118 0 : outb_p(0x30, PIT_MODE);
119 :
120 0 : if (i8253_clear_counter_on_shutdown) {
121 0 : outb_p(0, PIT_CH0);
122 0 : outb_p(0, PIT_CH0);
123 : }
124 :
125 0 : raw_spin_unlock(&i8253_lock);
126 0 : return 0;
127 : }
128 :
129 0 : static int pit_set_oneshot(struct clock_event_device *evt)
130 : {
131 0 : raw_spin_lock(&i8253_lock);
132 0 : outb_p(0x38, PIT_MODE);
133 0 : raw_spin_unlock(&i8253_lock);
134 0 : return 0;
135 : }
136 :
137 0 : static int pit_set_periodic(struct clock_event_device *evt)
138 : {
139 0 : raw_spin_lock(&i8253_lock);
140 :
141 : /* binary, mode 2, LSB/MSB, ch 0 */
142 0 : outb_p(0x34, PIT_MODE);
143 0 : outb_p(PIT_LATCH & 0xff, PIT_CH0); /* LSB */
144 0 : outb_p(PIT_LATCH >> 8, PIT_CH0); /* MSB */
145 :
146 0 : raw_spin_unlock(&i8253_lock);
147 0 : return 0;
148 : }
149 :
150 : /*
151 : * Program the next event in oneshot mode
152 : *
153 : * Delta is given in PIT ticks
154 : */
155 0 : static int pit_next_event(unsigned long delta, struct clock_event_device *evt)
156 : {
157 0 : raw_spin_lock(&i8253_lock);
158 0 : outb_p(delta & 0xff , PIT_CH0); /* LSB */
159 0 : outb_p(delta >> 8 , PIT_CH0); /* MSB */
160 0 : raw_spin_unlock(&i8253_lock);
161 :
162 0 : 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 : */
169 : struct 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 : */
181 0 : void __init clockevent_i8253_init(bool oneshot)
182 : {
183 0 : if (oneshot) {
184 0 : i8253_clockevent.features |= CLOCK_EVT_FEAT_ONESHOT;
185 0 : 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 0 : i8253_clockevent.cpumask = cpumask_of(smp_processor_id());
192 :
193 0 : clockevents_config_and_register(&i8253_clockevent, PIT_TICK_RATE,
194 : 0xF, 0x7FFF);
195 0 : }
196 : #endif
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