cs5535-clockevt.c revision fdb19a6cb48407c59a2007063f4005c9384603c3 
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
24static int timer_irq;
25module_param_named(irq, timer_irq, int, 0644);
26MODULE_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
45static unsigned int cs5535_tick_mode = CLOCK_EVT_MODE_SHUTDOWN;
46static 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
63static 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
71static 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
80static 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
91static 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
97static 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	.cpumask = cpu_all_mask,
104	.shift = 32
105};
106
107static irqreturn_t mfgpt_tick(int irq, void *dev_id)
108{
109	uint16_t val = cs5535_mfgpt_read(cs5535_event_clock, MFGPT_REG_SETUP);
110
111	/* See if the interrupt was for us */
112	if (!(val & (MFGPT_SETUP_SETUP | MFGPT_SETUP_CMP2 | MFGPT_SETUP_CMP1)))
113		return IRQ_NONE;
114
115	/* Turn off the clock (and clear the event) */
116	disable_timer(cs5535_event_clock);
117
118	if (cs5535_tick_mode == CLOCK_EVT_MODE_SHUTDOWN)
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 (cs5535_tick_mode == CLOCK_EVT_MODE_PERIODIC)
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
134static struct irqaction mfgptirq  = {
135	.handler = mfgpt_tick,
136	.flags = IRQF_DISABLED | IRQF_NOBALANCING | IRQF_TIMER,
137	.name = DRV_NAME,
138};
139
140static int __init cs5535_mfgpt_init(void)
141{
142	struct cs5535_mfgpt_timer *timer;
143	int ret;
144	uint16_t val;
145
146	timer = cs5535_mfgpt_alloc_timer(MFGPT_TIMER_ANY, MFGPT_DOMAIN_WORKING);
147	if (!timer) {
148		printk(KERN_ERR DRV_NAME ": Could not allocate MFPGT timer\n");
149		return -ENODEV;
150	}
151	cs5535_event_clock = timer;
152
153	/* Set up the IRQ on the MFGPT side */
154	if (cs5535_mfgpt_setup_irq(timer, MFGPT_CMP2, &timer_irq)) {
155		printk(KERN_ERR DRV_NAME ": Could not set up IRQ %d\n",
156				timer_irq);
157		goto err_timer;
158	}
159
160	/* And register it with the kernel */
161	ret = setup_irq(timer_irq, &mfgptirq);
162	if (ret) {
163		printk(KERN_ERR DRV_NAME ": Unable to set up the interrupt.\n");
164		goto err_irq;
165	}
166
167	/* Set the clock scale and enable the event mode for CMP2 */
168	val = MFGPT_SCALE | (3 << 8);
169
170	cs5535_mfgpt_write(cs5535_event_clock, MFGPT_REG_SETUP, val);
171
172	/* Set up the clock event */
173	cs5535_clockevent.mult = div_sc(MFGPT_HZ, NSEC_PER_SEC,
174			cs5535_clockevent.shift);
175	cs5535_clockevent.min_delta_ns = clockevent_delta2ns(0xF,
176			&cs5535_clockevent);
177	cs5535_clockevent.max_delta_ns = clockevent_delta2ns(0xFFFE,
178			&cs5535_clockevent);
179
180	printk(KERN_INFO DRV_NAME
181		": Registering MFGPT timer as a clock event, using IRQ %d\n",
182		timer_irq);
183	clockevents_register_device(&cs5535_clockevent);
184
185	return 0;
186
187err_irq:
188	cs5535_mfgpt_release_irq(cs5535_event_clock, MFGPT_CMP2, &timer_irq);
189err_timer:
190	cs5535_mfgpt_free_timer(cs5535_event_clock);
191	printk(KERN_ERR DRV_NAME ": Unable to set up the MFGPT clock source\n");
192	return -EIO;
193}
194
195module_init(cs5535_mfgpt_init);
196
197MODULE_AUTHOR("Andres Salomon <dilinger@collabora.co.uk>");
198MODULE_DESCRIPTION("CS5535/CS5536 MFGPT clock event driver");
199MODULE_LICENSE("GPL");
200