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 struct cs5535_mfgpt_timer *cs5535_event_clock;
46
47/* Selected from the table above */
48
49#define MFGPT_DIVISOR 16
50#define MFGPT_SCALE  4     /* divisor = 2^(scale) */
51#define MFGPT_HZ  (32768 / MFGPT_DIVISOR)
52#define MFGPT_PERIODIC (MFGPT_HZ / HZ)
53
54/*
55 * The MFGPT timers on the CS5536 provide us with suitable timers to use
56 * as clock event sources - not as good as a HPET or APIC, but certainly
57 * better than the PIT.  This isn't a general purpose MFGPT driver, but
58 * a simplified one designed specifically to act as a clock event source.
59 * For full details about the MFGPT, please consult the CS5536 data sheet.
60 */
61
62static void disable_timer(struct cs5535_mfgpt_timer *timer)
63{
64	/* avoid races by clearing CMP1 and CMP2 unconditionally */
65	cs5535_mfgpt_write(timer, MFGPT_REG_SETUP,
66			(uint16_t) ~MFGPT_SETUP_CNTEN | MFGPT_SETUP_CMP1 |
67				MFGPT_SETUP_CMP2);
68}
69
70static void start_timer(struct cs5535_mfgpt_timer *timer, uint16_t delta)
71{
72	cs5535_mfgpt_write(timer, MFGPT_REG_CMP2, delta);
73	cs5535_mfgpt_write(timer, MFGPT_REG_COUNTER, 0);
74
75	cs5535_mfgpt_write(timer, MFGPT_REG_SETUP,
76			MFGPT_SETUP_CNTEN | MFGPT_SETUP_CMP2);
77}
78
79static int mfgpt_shutdown(struct clock_event_device *evt)
80{
81	disable_timer(cs5535_event_clock);
82	return 0;
83}
84
85static int mfgpt_set_periodic(struct clock_event_device *evt)
86{
87	disable_timer(cs5535_event_clock);
88	start_timer(cs5535_event_clock, MFGPT_PERIODIC);
89	return 0;
90}
91
92static int mfgpt_next_event(unsigned long delta, struct clock_event_device *evt)
93{
94	start_timer(cs5535_event_clock, delta);
95	return 0;
96}
97
98static struct clock_event_device cs5535_clockevent = {
99	.name = DRV_NAME,
100	.features = CLOCK_EVT_FEAT_PERIODIC | CLOCK_EVT_FEAT_ONESHOT,
101	.set_state_shutdown = mfgpt_shutdown,
102	.set_state_periodic = mfgpt_set_periodic,
103	.set_state_oneshot = mfgpt_shutdown,
104	.tick_resume = mfgpt_shutdown,
105	.set_next_event = mfgpt_next_event,
106	.rating = 250,
107};
108
109static irqreturn_t mfgpt_tick(int irq, void *dev_id)
110{
111	uint16_t val = cs5535_mfgpt_read(cs5535_event_clock, MFGPT_REG_SETUP);
112
113	/* See if the interrupt was for us */
114	if (!(val & (MFGPT_SETUP_SETUP | MFGPT_SETUP_CMP2 | MFGPT_SETUP_CMP1)))
115		return IRQ_NONE;
116
117	/* Turn off the clock (and clear the event) */
118	disable_timer(cs5535_event_clock);
119
120	if (clockevent_state_shutdown(&cs5535_clockevent))
121		return IRQ_HANDLED;
122
123	/* Clear the counter */
124	cs5535_mfgpt_write(cs5535_event_clock, MFGPT_REG_COUNTER, 0);
125
126	/* Restart the clock in periodic mode */
127
128	if (clockevent_state_periodic(&cs5535_clockevent))
129		cs5535_mfgpt_write(cs5535_event_clock, MFGPT_REG_SETUP,
130				MFGPT_SETUP_CNTEN | MFGPT_SETUP_CMP2);
131
132	cs5535_clockevent.event_handler(&cs5535_clockevent);
133	return IRQ_HANDLED;
134}
135
136static struct irqaction mfgptirq  = {
137	.handler = mfgpt_tick,
138	.flags = IRQF_NOBALANCING | IRQF_TIMER | IRQF_SHARED,
139	.name = DRV_NAME,
140};
141
142static int __init cs5535_mfgpt_init(void)
143{
144	struct cs5535_mfgpt_timer *timer;
145	int ret;
146	uint16_t val;
147
148	timer = cs5535_mfgpt_alloc_timer(MFGPT_TIMER_ANY, MFGPT_DOMAIN_WORKING);
149	if (!timer) {
150		printk(KERN_ERR DRV_NAME ": Could not allocate MFGPT timer\n");
151		return -ENODEV;
152	}
153	cs5535_event_clock = timer;
154
155	/* Set up the IRQ on the MFGPT side */
156	if (cs5535_mfgpt_setup_irq(timer, MFGPT_CMP2, &timer_irq)) {
157		printk(KERN_ERR DRV_NAME ": Could not set up IRQ %d\n",
158				timer_irq);
159		goto err_timer;
160	}
161
162	/* And register it with the kernel */
163	ret = setup_irq(timer_irq, &mfgptirq);
164	if (ret) {
165		printk(KERN_ERR DRV_NAME ": Unable to set up the interrupt.\n");
166		goto err_irq;
167	}
168
169	/* Set the clock scale and enable the event mode for CMP2 */
170	val = MFGPT_SCALE | (3 << 8);
171
172	cs5535_mfgpt_write(cs5535_event_clock, MFGPT_REG_SETUP, val);
173
174	/* Set up the clock event */
175	printk(KERN_INFO DRV_NAME
176		": Registering MFGPT timer as a clock event, using IRQ %d\n",
177		timer_irq);
178	clockevents_config_and_register(&cs5535_clockevent, MFGPT_HZ,
179					0xF, 0xFFFE);
180
181	return 0;
182
183err_irq:
184	cs5535_mfgpt_release_irq(cs5535_event_clock, MFGPT_CMP2, &timer_irq);
185err_timer:
186	cs5535_mfgpt_free_timer(cs5535_event_clock);
187	printk(KERN_ERR DRV_NAME ": Unable to set up the MFGPT clock source\n");
188	return -EIO;
189}
190
191module_init(cs5535_mfgpt_init);
192
193MODULE_AUTHOR("Andres Salomon <dilinger@queued.net>");
194MODULE_DESCRIPTION("CS5535/CS5536 MFGPT clock event driver");
195MODULE_LICENSE("GPL");
196