1 // SPDX-License-Identifier: GPL-2.0-or-later
2 /*
3 * linux/arch/arm/mach-at91/at91rm9200_time.c
4 *
5 * Copyright (C) 2003 SAN People
6 * Copyright (C) 2003 ATMEL
7 */
8
9 #include <linux/kernel.h>
10 #include <linux/interrupt.h>
11 #include <linux/irq.h>
12 #include <linux/clk.h>
13 #include <linux/clockchips.h>
14 #include <linux/export.h>
15 #include <linux/mfd/syscon.h>
16 #include <linux/mfd/syscon/atmel-st.h>
17 #include <linux/of_irq.h>
18 #include <linux/regmap.h>
19
20 static unsigned long last_crtr;
21 static u32 irqmask;
22 static struct clock_event_device clkevt;
23 static struct regmap *regmap_st;
24 static int timer_latch;
25
26 /*
27 * The ST_CRTR is updated asynchronously to the master clock ... but
28 * the updates as seen by the CPU don't seem to be strictly monotonic.
29 * Waiting until we read the same value twice avoids glitching.
30 */
read_CRTR(void)31 static inline unsigned long read_CRTR(void)
32 {
33 unsigned int x1, x2;
34
35 regmap_read(regmap_st, AT91_ST_CRTR, &x1);
36 do {
37 regmap_read(regmap_st, AT91_ST_CRTR, &x2);
38 if (x1 == x2)
39 break;
40 x1 = x2;
41 } while (1);
42 return x1;
43 }
44
45 /*
46 * IRQ handler for the timer.
47 */
at91rm9200_timer_interrupt(int irq,void * dev_id)48 static irqreturn_t at91rm9200_timer_interrupt(int irq, void *dev_id)
49 {
50 u32 sr;
51
52 regmap_read(regmap_st, AT91_ST_SR, &sr);
53 sr &= irqmask;
54
55 /*
56 * irqs should be disabled here, but as the irq is shared they are only
57 * guaranteed to be off if the timer irq is registered first.
58 */
59 WARN_ON_ONCE(!irqs_disabled());
60
61 /* simulate "oneshot" timer with alarm */
62 if (sr & AT91_ST_ALMS) {
63 clkevt.event_handler(&clkevt);
64 return IRQ_HANDLED;
65 }
66
67 /* periodic mode should handle delayed ticks */
68 if (sr & AT91_ST_PITS) {
69 u32 crtr = read_CRTR();
70
71 while (((crtr - last_crtr) & AT91_ST_CRTV) >= timer_latch) {
72 last_crtr += timer_latch;
73 clkevt.event_handler(&clkevt);
74 }
75 return IRQ_HANDLED;
76 }
77
78 /* this irq is shared ... */
79 return IRQ_NONE;
80 }
81
read_clk32k(struct clocksource * cs)82 static u64 read_clk32k(struct clocksource *cs)
83 {
84 return read_CRTR();
85 }
86
87 static struct clocksource clk32k = {
88 .name = "32k_counter",
89 .rating = 150,
90 .read = read_clk32k,
91 .mask = CLOCKSOURCE_MASK(20),
92 .flags = CLOCK_SOURCE_IS_CONTINUOUS,
93 };
94
clkdev32k_disable_and_flush_irq(void)95 static void clkdev32k_disable_and_flush_irq(void)
96 {
97 unsigned int val;
98
99 /* Disable and flush pending timer interrupts */
100 regmap_write(regmap_st, AT91_ST_IDR, AT91_ST_PITS | AT91_ST_ALMS);
101 regmap_read(regmap_st, AT91_ST_SR, &val);
102 last_crtr = read_CRTR();
103 }
104
clkevt32k_shutdown(struct clock_event_device * evt)105 static int clkevt32k_shutdown(struct clock_event_device *evt)
106 {
107 clkdev32k_disable_and_flush_irq();
108 irqmask = 0;
109 regmap_write(regmap_st, AT91_ST_IER, irqmask);
110 return 0;
111 }
112
clkevt32k_set_oneshot(struct clock_event_device * dev)113 static int clkevt32k_set_oneshot(struct clock_event_device *dev)
114 {
115 clkdev32k_disable_and_flush_irq();
116
117 /*
118 * ALM for oneshot irqs, set by next_event()
119 * before 32 seconds have passed.
120 */
121 irqmask = AT91_ST_ALMS;
122 regmap_write(regmap_st, AT91_ST_RTAR, last_crtr);
123 regmap_write(regmap_st, AT91_ST_IER, irqmask);
124 return 0;
125 }
126
clkevt32k_set_periodic(struct clock_event_device * dev)127 static int clkevt32k_set_periodic(struct clock_event_device *dev)
128 {
129 clkdev32k_disable_and_flush_irq();
130
131 /* PIT for periodic irqs; fixed rate of 1/HZ */
132 irqmask = AT91_ST_PITS;
133 regmap_write(regmap_st, AT91_ST_PIMR, timer_latch);
134 regmap_write(regmap_st, AT91_ST_IER, irqmask);
135 return 0;
136 }
137
138 static int
clkevt32k_next_event(unsigned long delta,struct clock_event_device * dev)139 clkevt32k_next_event(unsigned long delta, struct clock_event_device *dev)
140 {
141 u32 alm;
142 unsigned int val;
143
144 BUG_ON(delta < 2);
145
146 /* The alarm IRQ uses absolute time (now+delta), not the relative
147 * time (delta) in our calling convention. Like all clockevents
148 * using such "match" hardware, we have a race to defend against.
149 *
150 * Our defense here is to have set up the clockevent device so the
151 * delta is at least two. That way we never end up writing RTAR
152 * with the value then held in CRTR ... which would mean the match
153 * wouldn't trigger until 32 seconds later, after CRTR wraps.
154 */
155 alm = read_CRTR();
156
157 /* Cancel any pending alarm; flush any pending IRQ */
158 regmap_write(regmap_st, AT91_ST_RTAR, alm);
159 regmap_read(regmap_st, AT91_ST_SR, &val);
160
161 /* Schedule alarm by writing RTAR. */
162 alm += delta;
163 regmap_write(regmap_st, AT91_ST_RTAR, alm);
164
165 return 0;
166 }
167
168 static struct clock_event_device clkevt = {
169 .name = "at91_tick",
170 .features = CLOCK_EVT_FEAT_PERIODIC |
171 CLOCK_EVT_FEAT_ONESHOT,
172 .rating = 150,
173 .set_next_event = clkevt32k_next_event,
174 .set_state_shutdown = clkevt32k_shutdown,
175 .set_state_periodic = clkevt32k_set_periodic,
176 .set_state_oneshot = clkevt32k_set_oneshot,
177 .tick_resume = clkevt32k_shutdown,
178 };
179
180 /*
181 * ST (system timer) module supports both clockevents and clocksource.
182 */
atmel_st_timer_init(struct device_node * node)183 static int __init atmel_st_timer_init(struct device_node *node)
184 {
185 struct clk *sclk;
186 unsigned int sclk_rate, val;
187 int irq, ret;
188
189 regmap_st = syscon_node_to_regmap(node);
190 if (IS_ERR(regmap_st)) {
191 pr_err("Unable to get regmap\n");
192 return PTR_ERR(regmap_st);
193 }
194
195 /* Disable all timer interrupts, and clear any pending ones */
196 regmap_write(regmap_st, AT91_ST_IDR,
197 AT91_ST_PITS | AT91_ST_WDOVF | AT91_ST_RTTINC | AT91_ST_ALMS);
198 regmap_read(regmap_st, AT91_ST_SR, &val);
199
200 /* Get the interrupts property */
201 irq = irq_of_parse_and_map(node, 0);
202 if (!irq) {
203 pr_err("Unable to get IRQ from DT\n");
204 return -EINVAL;
205 }
206
207 /* Make IRQs happen for the system timer */
208 ret = request_irq(irq, at91rm9200_timer_interrupt,
209 IRQF_SHARED | IRQF_TIMER | IRQF_IRQPOLL,
210 "at91_tick", regmap_st);
211 if (ret) {
212 pr_err("Unable to setup IRQ\n");
213 return ret;
214 }
215
216 sclk = of_clk_get(node, 0);
217 if (IS_ERR(sclk)) {
218 pr_err("Unable to get slow clock\n");
219 return PTR_ERR(sclk);
220 }
221
222 ret = clk_prepare_enable(sclk);
223 if (ret) {
224 pr_err("Could not enable slow clock\n");
225 return ret;
226 }
227
228 sclk_rate = clk_get_rate(sclk);
229 if (!sclk_rate) {
230 pr_err("Invalid slow clock rate\n");
231 return -EINVAL;
232 }
233 timer_latch = (sclk_rate + HZ / 2) / HZ;
234
235 /* The 32KiHz "Slow Clock" (tick every 30517.58 nanoseconds) is used
236 * directly for the clocksource and all clockevents, after adjusting
237 * its prescaler from the 1 Hz default.
238 */
239 regmap_write(regmap_st, AT91_ST_RTMR, 1);
240
241 /* Setup timer clockevent, with minimum of two ticks (important!!) */
242 clkevt.cpumask = cpumask_of(0);
243 clockevents_config_and_register(&clkevt, sclk_rate,
244 2, AT91_ST_ALMV);
245
246 /* register clocksource */
247 return clocksource_register_hz(&clk32k, sclk_rate);
248 }
249 TIMER_OF_DECLARE(atmel_st_timer, "atmel,at91rm9200-st",
250 atmel_st_timer_init);
251