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	.shift = 32
104};
105
106static 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
133static struct irqaction mfgptirq  = {
134	.handler = mfgpt_tick,
135	.flags = IRQF_DISABLED | IRQF_NOBALANCING | IRQF_TIMER | IRQF_SHARED,
136	.name = DRV_NAME,
137};
138
139static 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
186err_irq:
187	cs5535_mfgpt_release_irq(cs5535_event_clock, MFGPT_CMP2, &timer_irq);
188err_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
194module_init(cs5535_mfgpt_init);
195
196MODULE_AUTHOR("Andres Salomon <dilinger@queued.net>");
197MODULE_DESCRIPTION("CS5535/CS5536 MFGPT clock event driver");
198MODULE_LICENSE("GPL");