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