1 /*
2  * J-Core SoC PIT/clocksource driver
3  *
4  * Copyright (C) 2015-2016 Smart Energy Instruments, Inc.
5  *
6  * This file is subject to the terms and conditions of the GNU General Public
7  * License.  See the file "COPYING" in the main directory of this archive
8  * for more details.
9  */
10 
11 #include <linux/kernel.h>
12 #include <linux/slab.h>
13 #include <linux/interrupt.h>
14 #include <linux/clockchips.h>
15 #include <linux/clocksource.h>
16 #include <linux/sched_clock.h>
17 #include <linux/cpu.h>
18 #include <linux/cpuhotplug.h>
19 #include <linux/of_address.h>
20 #include <linux/of_irq.h>
21 
22 #define PIT_IRQ_SHIFT		12
23 #define PIT_PRIO_SHIFT		20
24 #define PIT_ENABLE_SHIFT	26
25 #define PIT_PRIO_MASK		0xf
26 
27 #define REG_PITEN		0x00
28 #define REG_THROT		0x10
29 #define REG_COUNT		0x14
30 #define REG_BUSPD		0x18
31 #define REG_SECHI		0x20
32 #define REG_SECLO		0x24
33 #define REG_NSEC		0x28
34 
35 struct jcore_pit {
36 	struct clock_event_device	ced;
37 	void __iomem			*base;
38 	unsigned long			periodic_delta;
39 	u32				enable_val;
40 };
41 
42 static void __iomem *jcore_pit_base;
43 static struct jcore_pit __percpu *jcore_pit_percpu;
44 
45 static notrace u64 jcore_sched_clock_read(void)
46 {
47 	u32 seclo, nsec, seclo0;
48 	__iomem void *base = jcore_pit_base;
49 
50 	seclo = readl(base + REG_SECLO);
51 	do {
52 		seclo0 = seclo;
53 		nsec  = readl(base + REG_NSEC);
54 		seclo = readl(base + REG_SECLO);
55 	} while (seclo0 != seclo);
56 
57 	return seclo * NSEC_PER_SEC + nsec;
58 }
59 
60 static u64 jcore_clocksource_read(struct clocksource *cs)
61 {
62 	return jcore_sched_clock_read();
63 }
64 
65 static int jcore_pit_disable(struct jcore_pit *pit)
66 {
67 	writel(0, pit->base + REG_PITEN);
68 	return 0;
69 }
70 
71 static int jcore_pit_set(unsigned long delta, struct jcore_pit *pit)
72 {
73 	jcore_pit_disable(pit);
74 	writel(delta, pit->base + REG_THROT);
75 	writel(pit->enable_val, pit->base + REG_PITEN);
76 	return 0;
77 }
78 
79 static int jcore_pit_set_state_shutdown(struct clock_event_device *ced)
80 {
81 	struct jcore_pit *pit = container_of(ced, struct jcore_pit, ced);
82 
83 	return jcore_pit_disable(pit);
84 }
85 
86 static int jcore_pit_set_state_oneshot(struct clock_event_device *ced)
87 {
88 	struct jcore_pit *pit = container_of(ced, struct jcore_pit, ced);
89 
90 	return jcore_pit_disable(pit);
91 }
92 
93 static int jcore_pit_set_state_periodic(struct clock_event_device *ced)
94 {
95 	struct jcore_pit *pit = container_of(ced, struct jcore_pit, ced);
96 
97 	return jcore_pit_set(pit->periodic_delta, pit);
98 }
99 
100 static int jcore_pit_set_next_event(unsigned long delta,
101 				    struct clock_event_device *ced)
102 {
103 	struct jcore_pit *pit = container_of(ced, struct jcore_pit, ced);
104 
105 	return jcore_pit_set(delta, pit);
106 }
107 
108 static int jcore_pit_local_init(unsigned cpu)
109 {
110 	struct jcore_pit *pit = this_cpu_ptr(jcore_pit_percpu);
111 	unsigned buspd, freq;
112 
113 	pr_info("Local J-Core PIT init on cpu %u\n", cpu);
114 
115 	buspd = readl(pit->base + REG_BUSPD);
116 	freq = DIV_ROUND_CLOSEST(NSEC_PER_SEC, buspd);
117 	pit->periodic_delta = DIV_ROUND_CLOSEST(NSEC_PER_SEC, HZ * buspd);
118 
119 	clockevents_config_and_register(&pit->ced, freq, 1, ULONG_MAX);
120 
121 	return 0;
122 }
123 
124 static irqreturn_t jcore_timer_interrupt(int irq, void *dev_id)
125 {
126 	struct jcore_pit *pit = this_cpu_ptr(dev_id);
127 
128 	if (clockevent_state_oneshot(&pit->ced))
129 		jcore_pit_disable(pit);
130 
131 	pit->ced.event_handler(&pit->ced);
132 
133 	return IRQ_HANDLED;
134 }
135 
136 static int __init jcore_pit_init(struct device_node *node)
137 {
138 	int err;
139 	unsigned pit_irq, cpu;
140 	unsigned long hwirq;
141 	u32 irqprio, enable_val;
142 
143 	jcore_pit_base = of_iomap(node, 0);
144 	if (!jcore_pit_base) {
145 		pr_err("Error: Cannot map base address for J-Core PIT\n");
146 		return -ENXIO;
147 	}
148 
149 	pit_irq = irq_of_parse_and_map(node, 0);
150 	if (!pit_irq) {
151 		pr_err("Error: J-Core PIT has no IRQ\n");
152 		return -ENXIO;
153 	}
154 
155 	pr_info("Initializing J-Core PIT at %p IRQ %d\n",
156 		jcore_pit_base, pit_irq);
157 
158 	err = clocksource_mmio_init(jcore_pit_base, "jcore_pit_cs",
159 				    NSEC_PER_SEC, 400, 32,
160 				    jcore_clocksource_read);
161 	if (err) {
162 		pr_err("Error registering clocksource device: %d\n", err);
163 		return err;
164 	}
165 
166 	sched_clock_register(jcore_sched_clock_read, 32, NSEC_PER_SEC);
167 
168 	jcore_pit_percpu = alloc_percpu(struct jcore_pit);
169 	if (!jcore_pit_percpu) {
170 		pr_err("Failed to allocate memory for clock event device\n");
171 		return -ENOMEM;
172 	}
173 
174 	err = request_irq(pit_irq, jcore_timer_interrupt,
175 			  IRQF_TIMER | IRQF_PERCPU,
176 			  "jcore_pit", jcore_pit_percpu);
177 	if (err) {
178 		pr_err("pit irq request failed: %d\n", err);
179 		free_percpu(jcore_pit_percpu);
180 		return err;
181 	}
182 
183 	/*
184 	 * The J-Core PIT is not hard-wired to a particular IRQ, but
185 	 * integrated with the interrupt controller such that the IRQ it
186 	 * generates is programmable, as follows:
187 	 *
188 	 * The bit layout of the PIT enable register is:
189 	 *
190 	 *	.....e..ppppiiiiiiii............
191 	 *
192 	 * where the .'s indicate unrelated/unused bits, e is enable,
193 	 * p is priority, and i is hard irq number.
194 	 *
195 	 * For the PIT included in AIC1 (obsolete but still in use),
196 	 * any hard irq (trap number) can be programmed via the 8
197 	 * iiiiiiii bits, and a priority (0-15) is programmable
198 	 * separately in the pppp bits.
199 	 *
200 	 * For the PIT included in AIC2 (current), the programming
201 	 * interface is equivalent modulo interrupt mapping. This is
202 	 * why a different compatible tag was not used. However only
203 	 * traps 64-127 (the ones actually intended to be used for
204 	 * interrupts, rather than syscalls/exceptions/etc.) can be
205 	 * programmed (the high 2 bits of i are ignored) and the
206 	 * priority pppp is <<2'd and or'd onto the irq number. This
207 	 * choice seems to have been made on the hardware engineering
208 	 * side under an assumption that preserving old AIC1 priority
209 	 * mappings was important. Future models will likely ignore
210 	 * the pppp field.
211 	 */
212 	hwirq = irq_get_irq_data(pit_irq)->hwirq;
213 	irqprio = (hwirq >> 2) & PIT_PRIO_MASK;
214 	enable_val = (1U << PIT_ENABLE_SHIFT)
215 		   | (hwirq << PIT_IRQ_SHIFT)
216 		   | (irqprio << PIT_PRIO_SHIFT);
217 
218 	for_each_present_cpu(cpu) {
219 		struct jcore_pit *pit = per_cpu_ptr(jcore_pit_percpu, cpu);
220 
221 		pit->base = of_iomap(node, cpu);
222 		if (!pit->base) {
223 			pr_err("Unable to map PIT for cpu %u\n", cpu);
224 			continue;
225 		}
226 
227 		pit->ced.name = "jcore_pit";
228 		pit->ced.features = CLOCK_EVT_FEAT_PERIODIC
229 				  | CLOCK_EVT_FEAT_ONESHOT
230 				  | CLOCK_EVT_FEAT_PERCPU;
231 		pit->ced.cpumask = cpumask_of(cpu);
232 		pit->ced.rating = 400;
233 		pit->ced.irq = pit_irq;
234 		pit->ced.set_state_shutdown = jcore_pit_set_state_shutdown;
235 		pit->ced.set_state_periodic = jcore_pit_set_state_periodic;
236 		pit->ced.set_state_oneshot = jcore_pit_set_state_oneshot;
237 		pit->ced.set_next_event = jcore_pit_set_next_event;
238 
239 		pit->enable_val = enable_val;
240 	}
241 
242 	cpuhp_setup_state(CPUHP_AP_JCORE_TIMER_STARTING,
243 			  "clockevents/jcore:starting",
244 			  jcore_pit_local_init, NULL);
245 
246 	return 0;
247 }
248 
249 CLOCKSOURCE_OF_DECLARE(jcore_pit, "jcore,pit", jcore_pit_init);
250