1 /*
2 * at91sam926x_time.c - Periodic Interval Timer (PIT) for at91sam926x
3 *
4 * Copyright (C) 2005-2006 M. Amine SAYA, ATMEL Rousset, France
5 * Revision 2005 M. Nicolas Diremdjian, ATMEL Rousset, France
6 * Converted to ClockSource/ClockEvents by David Brownell.
7 *
8 * This program is free software; you can redistribute it and/or modify
9 * it under the terms of the GNU General Public License version 2 as
10 * published by the Free Software Foundation.
11 */
12 #include <linux/interrupt.h>
13 #include <linux/irq.h>
14 #include <linux/kernel.h>
15 #include <linux/clk.h>
16 #include <linux/clockchips.h>
17
18 #include <asm/mach/time.h>
19
20 #include <mach/at91_pit.h>
21
22
23 #define PIT_CPIV(x) ((x) & AT91_PIT_CPIV)
24 #define PIT_PICNT(x) (((x) & AT91_PIT_PICNT) >> 20)
25
26 static u32 pit_cycle; /* write-once */
27 static u32 pit_cnt; /* access only w/system irq blocked */
28
29
30 /*
31 * Clocksource: just a monotonic counter of MCK/16 cycles.
32 * We don't care whether or not PIT irqs are enabled.
33 */
read_pit_clk(struct clocksource * cs)34 static cycle_t read_pit_clk(struct clocksource *cs)
35 {
36 unsigned long flags;
37 u32 elapsed;
38 u32 t;
39
40 raw_local_irq_save(flags);
41 elapsed = pit_cnt;
42 t = at91_sys_read(AT91_PIT_PIIR);
43 raw_local_irq_restore(flags);
44
45 elapsed += PIT_PICNT(t) * pit_cycle;
46 elapsed += PIT_CPIV(t);
47 return elapsed;
48 }
49
50 static struct clocksource pit_clk = {
51 .name = "pit",
52 .rating = 175,
53 .read = read_pit_clk,
54 .flags = CLOCK_SOURCE_IS_CONTINUOUS,
55 };
56
57
58 /*
59 * Clockevent device: interrupts every 1/HZ (== pit_cycles * MCK/16)
60 */
61 static void
pit_clkevt_mode(enum clock_event_mode mode,struct clock_event_device * dev)62 pit_clkevt_mode(enum clock_event_mode mode, struct clock_event_device *dev)
63 {
64 switch (mode) {
65 case CLOCK_EVT_MODE_PERIODIC:
66 /* update clocksource counter */
67 pit_cnt += pit_cycle * PIT_PICNT(at91_sys_read(AT91_PIT_PIVR));
68 at91_sys_write(AT91_PIT_MR, (pit_cycle - 1) | AT91_PIT_PITEN
69 | AT91_PIT_PITIEN);
70 break;
71 case CLOCK_EVT_MODE_ONESHOT:
72 BUG();
73 /* FALLTHROUGH */
74 case CLOCK_EVT_MODE_SHUTDOWN:
75 case CLOCK_EVT_MODE_UNUSED:
76 /* disable irq, leaving the clocksource active */
77 at91_sys_write(AT91_PIT_MR, (pit_cycle - 1) | AT91_PIT_PITEN);
78 break;
79 case CLOCK_EVT_MODE_RESUME:
80 break;
81 }
82 }
83
84 static struct clock_event_device pit_clkevt = {
85 .name = "pit",
86 .features = CLOCK_EVT_FEAT_PERIODIC,
87 .shift = 32,
88 .rating = 100,
89 .set_mode = pit_clkevt_mode,
90 };
91
92
93 /*
94 * IRQ handler for the timer.
95 */
at91sam926x_pit_interrupt(int irq,void * dev_id)96 static irqreturn_t at91sam926x_pit_interrupt(int irq, void *dev_id)
97 {
98 /*
99 * irqs should be disabled here, but as the irq is shared they are only
100 * guaranteed to be off if the timer irq is registered first.
101 */
102 WARN_ON_ONCE(!irqs_disabled());
103
104 /* The PIT interrupt may be disabled, and is shared */
105 if ((pit_clkevt.mode == CLOCK_EVT_MODE_PERIODIC)
106 && (at91_sys_read(AT91_PIT_SR) & AT91_PIT_PITS)) {
107 unsigned nr_ticks;
108
109 /* Get number of ticks performed before irq, and ack it */
110 nr_ticks = PIT_PICNT(at91_sys_read(AT91_PIT_PIVR));
111 do {
112 pit_cnt += pit_cycle;
113 pit_clkevt.event_handler(&pit_clkevt);
114 nr_ticks--;
115 } while (nr_ticks);
116
117 return IRQ_HANDLED;
118 }
119
120 return IRQ_NONE;
121 }
122
123 static struct irqaction at91sam926x_pit_irq = {
124 .name = "at91_tick",
125 .flags = IRQF_SHARED | IRQF_DISABLED | IRQF_TIMER | IRQF_IRQPOLL,
126 .handler = at91sam926x_pit_interrupt
127 };
128
at91sam926x_pit_reset(void)129 static void at91sam926x_pit_reset(void)
130 {
131 /* Disable timer and irqs */
132 at91_sys_write(AT91_PIT_MR, 0);
133
134 /* Clear any pending interrupts, wait for PIT to stop counting */
135 while (PIT_CPIV(at91_sys_read(AT91_PIT_PIVR)) != 0)
136 cpu_relax();
137
138 /* Start PIT but don't enable IRQ */
139 at91_sys_write(AT91_PIT_MR, (pit_cycle - 1) | AT91_PIT_PITEN);
140 }
141
142 /*
143 * Set up both clocksource and clockevent support.
144 */
at91sam926x_pit_init(void)145 static void __init at91sam926x_pit_init(void)
146 {
147 unsigned long pit_rate;
148 unsigned bits;
149
150 /*
151 * Use our actual MCK to figure out how many MCK/16 ticks per
152 * 1/HZ period (instead of a compile-time constant LATCH).
153 */
154 pit_rate = clk_get_rate(clk_get(NULL, "mck")) / 16;
155 pit_cycle = (pit_rate + HZ/2) / HZ;
156 WARN_ON(((pit_cycle - 1) & ~AT91_PIT_PIV) != 0);
157
158 /* Initialize and enable the timer */
159 at91sam926x_pit_reset();
160
161 /*
162 * Register clocksource. The high order bits of PIV are unused,
163 * so this isn't a 32-bit counter unless we get clockevent irqs.
164 */
165 bits = 12 /* PICNT */ + ilog2(pit_cycle) /* PIV */;
166 pit_clk.mask = CLOCKSOURCE_MASK(bits);
167 clocksource_register_hz(&pit_clk, pit_rate);
168
169 /* Set up irq handler */
170 setup_irq(AT91_ID_SYS, &at91sam926x_pit_irq);
171
172 /* Set up and register clockevents */
173 pit_clkevt.mult = div_sc(pit_rate, NSEC_PER_SEC, pit_clkevt.shift);
174 pit_clkevt.cpumask = cpumask_of(0);
175 clockevents_register_device(&pit_clkevt);
176 }
177
at91sam926x_pit_suspend(void)178 static void at91sam926x_pit_suspend(void)
179 {
180 /* Disable timer */
181 at91_sys_write(AT91_PIT_MR, 0);
182 }
183
184 struct sys_timer at91sam926x_timer = {
185 .init = at91sam926x_pit_init,
186 .suspend = at91sam926x_pit_suspend,
187 .resume = at91sam926x_pit_reset,
188 };
189