1 /*
2 * Clock event driver for the CS5535/CS5536
3 *
4 * Copyright (C) 2006, Advanced Micro Devices, Inc.
5 * Copyright (C) 2007 Andres Salomon <dilinger@debian.org>
6 * Copyright (C) 2009 Andres Salomon <dilinger@collabora.co.uk>
7 *
8 * This program is free software; you can redistribute it and/or
9 * modify it under the terms of version 2 of the GNU General Public License
10 * as published by the Free Software Foundation.
11 *
12 * The MFGPTs are documented in AMD Geode CS5536 Companion Device Data Book.
13 */
14
15 #include <linux/kernel.h>
16 #include <linux/irq.h>
17 #include <linux/interrupt.h>
18 #include <linux/module.h>
19 #include <linux/cs5535.h>
20 #include <linux/clockchips.h>
21
22 #define DRV_NAME "cs5535-clockevt"
23
24 static int timer_irq;
25 module_param_named(irq, timer_irq, int, 0644);
26 MODULE_PARM_DESC(irq, "Which IRQ to use for the clock source MFGPT ticks.");
27
28 /*
29 * We are using the 32.768kHz input clock - it's the only one that has the
30 * ranges we find desirable. The following table lists the suitable
31 * divisors and the associated Hz, minimum interval and the maximum interval:
32 *
33 * Divisor Hz Min Delta (s) Max Delta (s)
34 * 1 32768 .00048828125 2.000
35 * 2 16384 .0009765625 4.000
36 * 4 8192 .001953125 8.000
37 * 8 4096 .00390625 16.000
38 * 16 2048 .0078125 32.000
39 * 32 1024 .015625 64.000
40 * 64 512 .03125 128.000
41 * 128 256 .0625 256.000
42 * 256 128 .125 512.000
43 */
44
45 static unsigned int cs5535_tick_mode = CLOCK_EVT_MODE_SHUTDOWN;
46 static struct cs5535_mfgpt_timer *cs5535_event_clock;
47
48 /* Selected from the table above */
49
50 #define MFGPT_DIVISOR 16
51 #define MFGPT_SCALE 4 /* divisor = 2^(scale) */
52 #define MFGPT_HZ (32768 / MFGPT_DIVISOR)
53 #define MFGPT_PERIODIC (MFGPT_HZ / HZ)
54
55 /*
56 * The MFPGT timers on the CS5536 provide us with suitable timers to use
57 * as clock event sources - not as good as a HPET or APIC, but certainly
58 * better than the PIT. This isn't a general purpose MFGPT driver, but
59 * a simplified one designed specifically to act as a clock event source.
60 * For full details about the MFGPT, please consult the CS5536 data sheet.
61 */
62
disable_timer(struct cs5535_mfgpt_timer * timer)63 static void disable_timer(struct cs5535_mfgpt_timer *timer)
64 {
65 /* avoid races by clearing CMP1 and CMP2 unconditionally */
66 cs5535_mfgpt_write(timer, MFGPT_REG_SETUP,
67 (uint16_t) ~MFGPT_SETUP_CNTEN | MFGPT_SETUP_CMP1 |
68 MFGPT_SETUP_CMP2);
69 }
70
start_timer(struct cs5535_mfgpt_timer * timer,uint16_t delta)71 static void start_timer(struct cs5535_mfgpt_timer *timer, uint16_t delta)
72 {
73 cs5535_mfgpt_write(timer, MFGPT_REG_CMP2, delta);
74 cs5535_mfgpt_write(timer, MFGPT_REG_COUNTER, 0);
75
76 cs5535_mfgpt_write(timer, MFGPT_REG_SETUP,
77 MFGPT_SETUP_CNTEN | MFGPT_SETUP_CMP2);
78 }
79
mfgpt_set_mode(enum clock_event_mode mode,struct clock_event_device * evt)80 static void mfgpt_set_mode(enum clock_event_mode mode,
81 struct clock_event_device *evt)
82 {
83 disable_timer(cs5535_event_clock);
84
85 if (mode == CLOCK_EVT_MODE_PERIODIC)
86 start_timer(cs5535_event_clock, MFGPT_PERIODIC);
87
88 cs5535_tick_mode = mode;
89 }
90
mfgpt_next_event(unsigned long delta,struct clock_event_device * evt)91 static int mfgpt_next_event(unsigned long delta, struct clock_event_device *evt)
92 {
93 start_timer(cs5535_event_clock, delta);
94 return 0;
95 }
96
97 static struct clock_event_device cs5535_clockevent = {
98 .name = DRV_NAME,
99 .features = CLOCK_EVT_FEAT_PERIODIC | CLOCK_EVT_FEAT_ONESHOT,
100 .set_mode = mfgpt_set_mode,
101 .set_next_event = mfgpt_next_event,
102 .rating = 250,
103 .shift = 32
104 };
105
mfgpt_tick(int irq,void * dev_id)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 (cs5535_tick_mode == CLOCK_EVT_MODE_SHUTDOWN)
118 return IRQ_HANDLED;
119
120 /* Clear the counter */
121 cs5535_mfgpt_write(cs5535_event_clock, MFGPT_REG_COUNTER, 0);
122
123 /* Restart the clock in periodic mode */
124
125 if (cs5535_tick_mode == CLOCK_EVT_MODE_PERIODIC)
126 cs5535_mfgpt_write(cs5535_event_clock, MFGPT_REG_SETUP,
127 MFGPT_SETUP_CNTEN | MFGPT_SETUP_CMP2);
128
129 cs5535_clockevent.event_handler(&cs5535_clockevent);
130 return IRQ_HANDLED;
131 }
132
133 static struct irqaction mfgptirq = {
134 .handler = mfgpt_tick,
135 .flags = IRQF_DISABLED | IRQF_NOBALANCING | IRQF_TIMER | IRQF_SHARED,
136 .name = DRV_NAME,
137 };
138
cs5535_mfgpt_init(void)139 static int __init cs5535_mfgpt_init(void)
140 {
141 struct cs5535_mfgpt_timer *timer;
142 int ret;
143 uint16_t val;
144
145 timer = cs5535_mfgpt_alloc_timer(MFGPT_TIMER_ANY, MFGPT_DOMAIN_WORKING);
146 if (!timer) {
147 printk(KERN_ERR DRV_NAME ": Could not allocate MFPGT timer\n");
148 return -ENODEV;
149 }
150 cs5535_event_clock = timer;
151
152 /* Set up the IRQ on the MFGPT side */
153 if (cs5535_mfgpt_setup_irq(timer, MFGPT_CMP2, &timer_irq)) {
154 printk(KERN_ERR DRV_NAME ": Could not set up IRQ %d\n",
155 timer_irq);
156 goto err_timer;
157 }
158
159 /* And register it with the kernel */
160 ret = setup_irq(timer_irq, &mfgptirq);
161 if (ret) {
162 printk(KERN_ERR DRV_NAME ": Unable to set up the interrupt.\n");
163 goto err_irq;
164 }
165
166 /* Set the clock scale and enable the event mode for CMP2 */
167 val = MFGPT_SCALE | (3 << 8);
168
169 cs5535_mfgpt_write(cs5535_event_clock, MFGPT_REG_SETUP, val);
170
171 /* Set up the clock event */
172 cs5535_clockevent.mult = div_sc(MFGPT_HZ, NSEC_PER_SEC,
173 cs5535_clockevent.shift);
174 cs5535_clockevent.min_delta_ns = clockevent_delta2ns(0xF,
175 &cs5535_clockevent);
176 cs5535_clockevent.max_delta_ns = clockevent_delta2ns(0xFFFE,
177 &cs5535_clockevent);
178
179 printk(KERN_INFO DRV_NAME
180 ": Registering MFGPT timer as a clock event, using IRQ %d\n",
181 timer_irq);
182 clockevents_register_device(&cs5535_clockevent);
183
184 return 0;
185
186 err_irq:
187 cs5535_mfgpt_release_irq(cs5535_event_clock, MFGPT_CMP2, &timer_irq);
188 err_timer:
189 cs5535_mfgpt_free_timer(cs5535_event_clock);
190 printk(KERN_ERR DRV_NAME ": Unable to set up the MFGPT clock source\n");
191 return -EIO;
192 }
193
194 module_init(cs5535_mfgpt_init);
195
196 MODULE_AUTHOR("Andres Salomon <dilinger@queued.net>");
197 MODULE_DESCRIPTION("CS5535/CS5536 MFGPT clock event driver");
198 MODULE_LICENSE("GPL");
199