1 // SPDX-License-Identifier: GPL-2.0-only
2 /*
3  * Clock event driver for the CS5535/CS5536
4  *
5  * Copyright (C) 2006, Advanced Micro Devices, Inc.
6  * Copyright (C) 2007  Andres Salomon <dilinger@debian.org>
7  * Copyright (C) 2009  Andres Salomon <dilinger@collabora.co.uk>
8  *
9  * The MFGPTs are documented in AMD Geode CS5536 Companion Device Data Book.
10  */
11 
12 #include <linux/kernel.h>
13 #include <linux/irq.h>
14 #include <linux/interrupt.h>
15 #include <linux/module.h>
16 #include <linux/cs5535.h>
17 #include <linux/clockchips.h>
18 
19 #define DRV_NAME "cs5535-clockevt"
20 
21 static int timer_irq;
22 module_param_hw_named(irq, timer_irq, int, irq, 0644);
23 MODULE_PARM_DESC(irq, "Which IRQ to use for the clock source MFGPT ticks.");
24 
25 /*
26  * We are using the 32.768kHz input clock - it's the only one that has the
27  * ranges we find desirable.  The following table lists the suitable
28  * divisors and the associated Hz, minimum interval and the maximum interval:
29  *
30  *  Divisor   Hz      Min Delta (s)  Max Delta (s)
31  *   1        32768   .00048828125      2.000
32  *   2        16384   .0009765625       4.000
33  *   4         8192   .001953125        8.000
34  *   8         4096   .00390625        16.000
35  *   16        2048   .0078125         32.000
36  *   32        1024   .015625          64.000
37  *   64         512   .03125          128.000
38  *  128         256   .0625           256.000
39  *  256         128   .125            512.000
40  */
41 
42 static struct cs5535_mfgpt_timer *cs5535_event_clock;
43 
44 /* Selected from the table above */
45 
46 #define MFGPT_DIVISOR 16
47 #define MFGPT_SCALE  4     /* divisor = 2^(scale) */
48 #define MFGPT_HZ  (32768 / MFGPT_DIVISOR)
49 #define MFGPT_PERIODIC (MFGPT_HZ / HZ)
50 
51 /*
52  * The MFGPT timers on the CS5536 provide us with suitable timers to use
53  * as clock event sources - not as good as a HPET or APIC, but certainly
54  * better than the PIT.  This isn't a general purpose MFGPT driver, but
55  * a simplified one designed specifically to act as a clock event source.
56  * For full details about the MFGPT, please consult the CS5536 data sheet.
57  */
58 
59 static void disable_timer(struct cs5535_mfgpt_timer *timer)
60 {
61 	/* avoid races by clearing CMP1 and CMP2 unconditionally */
62 	cs5535_mfgpt_write(timer, MFGPT_REG_SETUP,
63 			(uint16_t) ~MFGPT_SETUP_CNTEN | MFGPT_SETUP_CMP1 |
64 				MFGPT_SETUP_CMP2);
65 }
66 
67 static void start_timer(struct cs5535_mfgpt_timer *timer, uint16_t delta)
68 {
69 	cs5535_mfgpt_write(timer, MFGPT_REG_CMP2, delta);
70 	cs5535_mfgpt_write(timer, MFGPT_REG_COUNTER, 0);
71 
72 	cs5535_mfgpt_write(timer, MFGPT_REG_SETUP,
73 			MFGPT_SETUP_CNTEN | MFGPT_SETUP_CMP2);
74 }
75 
76 static int mfgpt_shutdown(struct clock_event_device *evt)
77 {
78 	disable_timer(cs5535_event_clock);
79 	return 0;
80 }
81 
82 static int mfgpt_set_periodic(struct clock_event_device *evt)
83 {
84 	disable_timer(cs5535_event_clock);
85 	start_timer(cs5535_event_clock, MFGPT_PERIODIC);
86 	return 0;
87 }
88 
89 static int mfgpt_next_event(unsigned long delta, struct clock_event_device *evt)
90 {
91 	start_timer(cs5535_event_clock, delta);
92 	return 0;
93 }
94 
95 static struct clock_event_device cs5535_clockevent = {
96 	.name = DRV_NAME,
97 	.features = CLOCK_EVT_FEAT_PERIODIC | CLOCK_EVT_FEAT_ONESHOT,
98 	.set_state_shutdown = mfgpt_shutdown,
99 	.set_state_periodic = mfgpt_set_periodic,
100 	.set_state_oneshot = mfgpt_shutdown,
101 	.tick_resume = mfgpt_shutdown,
102 	.set_next_event = mfgpt_next_event,
103 	.rating = 250,
104 };
105 
106 static irqreturn_t mfgpt_tick(int irq, void *dev_id)
107 {
108 	uint16_t val = cs5535_mfgpt_read(cs5535_event_clock, MFGPT_REG_SETUP);
109 
110 	/* See if the interrupt was for us */
111 	if (!(val & (MFGPT_SETUP_SETUP | MFGPT_SETUP_CMP2 | MFGPT_SETUP_CMP1)))
112 		return IRQ_NONE;
113 
114 	/* Turn off the clock (and clear the event) */
115 	disable_timer(cs5535_event_clock);
116 
117 	if (clockevent_state_detached(&cs5535_clockevent) ||
118 	    clockevent_state_shutdown(&cs5535_clockevent))
119 		return IRQ_HANDLED;
120 
121 	/* Clear the counter */
122 	cs5535_mfgpt_write(cs5535_event_clock, MFGPT_REG_COUNTER, 0);
123 
124 	/* Restart the clock in periodic mode */
125 
126 	if (clockevent_state_periodic(&cs5535_clockevent))
127 		cs5535_mfgpt_write(cs5535_event_clock, MFGPT_REG_SETUP,
128 				MFGPT_SETUP_CNTEN | MFGPT_SETUP_CMP2);
129 
130 	cs5535_clockevent.event_handler(&cs5535_clockevent);
131 	return IRQ_HANDLED;
132 }
133 
134 static int __init cs5535_mfgpt_init(void)
135 {
136 	unsigned long flags = IRQF_NOBALANCING | IRQF_TIMER | IRQF_SHARED;
137 	struct cs5535_mfgpt_timer *timer;
138 	int ret;
139 	uint16_t val;
140 
141 	timer = cs5535_mfgpt_alloc_timer(MFGPT_TIMER_ANY, MFGPT_DOMAIN_WORKING);
142 	if (!timer) {
143 		printk(KERN_ERR DRV_NAME ": Could not allocate MFGPT timer\n");
144 		return -ENODEV;
145 	}
146 	cs5535_event_clock = timer;
147 
148 	/* Set up the IRQ on the MFGPT side */
149 	if (cs5535_mfgpt_setup_irq(timer, MFGPT_CMP2, &timer_irq)) {
150 		printk(KERN_ERR DRV_NAME ": Could not set up IRQ %d\n",
151 				timer_irq);
152 		goto err_timer;
153 	}
154 
155 	/* And register it with the kernel */
156 	ret = request_irq(timer_irq, mfgpt_tick, flags, DRV_NAME, timer);
157 	if (ret) {
158 		printk(KERN_ERR DRV_NAME ": Unable to set up the interrupt.\n");
159 		goto err_irq;
160 	}
161 
162 	/* Set the clock scale and enable the event mode for CMP2 */
163 	val = MFGPT_SCALE | (3 << 8);
164 
165 	cs5535_mfgpt_write(cs5535_event_clock, MFGPT_REG_SETUP, val);
166 
167 	/* Set up the clock event */
168 	printk(KERN_INFO DRV_NAME
169 		": Registering MFGPT timer as a clock event, using IRQ %d\n",
170 		timer_irq);
171 	clockevents_config_and_register(&cs5535_clockevent, MFGPT_HZ,
172 					0xF, 0xFFFE);
173 
174 	return 0;
175 
176 err_irq:
177 	cs5535_mfgpt_release_irq(cs5535_event_clock, MFGPT_CMP2, &timer_irq);
178 err_timer:
179 	cs5535_mfgpt_free_timer(cs5535_event_clock);
180 	printk(KERN_ERR DRV_NAME ": Unable to set up the MFGPT clock source\n");
181 	return -EIO;
182 }
183 
184 module_init(cs5535_mfgpt_init);
185 
186 MODULE_AUTHOR("Andres Salomon <dilinger@queued.net>");
187 MODULE_DESCRIPTION("CS5535/CS5536 MFGPT clock event driver");
188 MODULE_LICENSE("GPL");
189