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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
21static int timer_irq;
22module_param_hw_named(irq, timer_irq, int, irq, 0644);
23MODULE_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
42static 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
59static 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
67static 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
76static int mfgpt_shutdown(struct clock_event_device *evt)
77{
78 disable_timer(cs5535_event_clock);
79 return 0;
80}
81
82static 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
89static 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
95static 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 .owner = THIS_MODULE,
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 (clockevent_state_detached(&cs5535_clockevent) ||
119 clockevent_state_shutdown(&cs5535_clockevent))
120 return IRQ_HANDLED;
121
122 /* Clear the counter */
123 cs5535_mfgpt_write(cs5535_event_clock, MFGPT_REG_COUNTER, 0);
124
125 /* Restart the clock in periodic mode */
126
127 if (clockevent_state_periodic(&cs5535_clockevent))
128 cs5535_mfgpt_write(cs5535_event_clock, MFGPT_REG_SETUP,
129 MFGPT_SETUP_CNTEN | MFGPT_SETUP_CMP2);
130
131 cs5535_clockevent.event_handler(&cs5535_clockevent);
132 return IRQ_HANDLED;
133}
134
135static int __init cs5535_mfgpt_init(void)
136{
137 unsigned long flags = IRQF_NOBALANCING | IRQF_TIMER | IRQF_SHARED;
138 struct cs5535_mfgpt_timer *timer;
139 int ret;
140 uint16_t val;
141
142 timer = cs5535_mfgpt_alloc_timer(MFGPT_TIMER_ANY, MFGPT_DOMAIN_WORKING);
143 if (!timer) {
144 printk(KERN_ERR DRV_NAME ": Could not allocate MFGPT timer\n");
145 return -ENODEV;
146 }
147 cs5535_event_clock = timer;
148
149 /* Set up the IRQ on the MFGPT side */
150 if (cs5535_mfgpt_setup_irq(timer, MFGPT_CMP2, &timer_irq)) {
151 printk(KERN_ERR DRV_NAME ": Could not set up IRQ %d\n",
152 timer_irq);
153 goto err_timer;
154 }
155
156 /* And register it with the kernel */
157 ret = request_irq(timer_irq, mfgpt_tick, flags, DRV_NAME, timer);
158 if (ret) {
159 printk(KERN_ERR DRV_NAME ": Unable to set up the interrupt.\n");
160 goto err_irq;
161 }
162
163 /* Set the clock scale and enable the event mode for CMP2 */
164 val = MFGPT_SCALE | (3 << 8);
165
166 cs5535_mfgpt_write(cs5535_event_clock, MFGPT_REG_SETUP, val);
167
168 /* Set up the clock event */
169 printk(KERN_INFO DRV_NAME
170 ": Registering MFGPT timer as a clock event, using IRQ %d\n",
171 timer_irq);
172 clockevents_config_and_register(&cs5535_clockevent, MFGPT_HZ,
173 0xF, 0xFFFE);
174
175 return 0;
176
177err_irq:
178 cs5535_mfgpt_release_irq(cs5535_event_clock, MFGPT_CMP2, &timer_irq);
179err_timer:
180 cs5535_mfgpt_free_timer(cs5535_event_clock);
181 printk(KERN_ERR DRV_NAME ": Unable to set up the MFGPT clock source\n");
182 return -EIO;
183}
184
185module_init(cs5535_mfgpt_init);
186
187MODULE_AUTHOR("Andres Salomon <dilinger@queued.net>");
188MODULE_DESCRIPTION("CS5535/CS5536 MFGPT clock event driver");
189MODULE_LICENSE("GPL");