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  */
i8253_read(struct clocksource * cs)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 
clocksource_i8253_init(void)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
pit_shutdown(struct clock_event_device * evt)111 static 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 
pit_set_oneshot(struct clock_event_device * evt)129 static 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 
pit_set_periodic(struct clock_event_device * evt)137 static 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  */
pit_next_event(unsigned long delta,struct clock_event_device * evt)155 static 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  */
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  */
clockevent_i8253_init(bool oneshot)181 void __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