1 /*
2 * This code largely moved from arch/i386/kernel/time.c.
3 * See comments there for proper credits.
4 */
5
6 #include <linux/spinlock.h>
7 #include <linux/module.h>
8 #include <linux/device.h>
9 #include <linux/irq.h>
10 #include <linux/sysdev.h>
11 #include <linux/timex.h>
12 #include <asm/delay.h>
13 #include <asm/mpspec.h>
14 #include <asm/timer.h>
15 #include <asm/smp.h>
16 #include <asm/io.h>
17 #include <asm/arch_hooks.h>
18
19 extern spinlock_t i8259A_lock;
20 extern spinlock_t i8253_lock;
21 #include "do_timer.h"
22 #include "io_ports.h"
23
24 static int count_p; /* counter in get_offset_pit() */
25
26 static int __init init_pit(char* override)
27 {
28 /* check clock override */
29 if (override[0] && strncmp(override,"pit",3))
30 printk(KERN_ERR "Warning: clock= override failed. Defaulting to PIT\n");
31
32 count_p = LATCH;
33 return 0;
34 }
35
36 static void mark_offset_pit(void)
37 {
38 /* nothing needed */
39 }
40
41 static unsigned long long monotonic_clock_pit(void)
42 {
43 return 0;
44 }
45
46 static void delay_pit(unsigned long loops)
47 {
48 int d0;
49 __asm__ __volatile__(
50 "\tjmp 1f\n"
51 ".align 16\n"
52 "1:\tjmp 2f\n"
53 ".align 16\n"
54 "2:\tdecl %0\n\tjns 2b"
55 :"=&a" (d0)
56 :"" (loops));
57 }
58
59
60 /* This function must be called with xtime_lock held.
61 * It was inspired by Steve McCanne's microtime-i386 for BSD. -- jrs
62 *
63 * However, the pc-audio speaker driver changes the divisor so that
64 * it gets interrupted rather more often - it loads 64 into the
65 * counter rather than 11932! This has an adverse impact on
66 * do_gettimeoffset() -- it stops working! What is also not
67 * good is that the interval that our timer function gets called
68 * is no longer 10.0002 ms, but 9.9767 ms. To get around this
69 * would require using a different timing source. Maybe someone
70 * could use the RTC - I know that this can interrupt at frequencies
71 * ranging from 8192Hz to 2Hz. If I had the energy, I'd somehow fix
72 * it so that at startup, the timer code in sched.c would select
73 * using either the RTC or the 8253 timer. The decision would be
74 * based on whether there was any other device around that needed
75 * to trample on the 8253. I'd set up the RTC to interrupt at 1024 Hz,
76 * and then do some jiggery to have a version of do_timer that
77 * advanced the clock by 1/1024 s. Every time that reached over 1/100
78 * of a second, then do all the old code. If the time was kept correct
79 * then do_gettimeoffset could just return 0 - there is no low order
80 * divider that can be accessed.
81 *
82 * Ideally, you would be able to use the RTC for the speaker driver,
83 * but it appears that the speaker driver really needs interrupt more
84 * often than every 120 us or so.
85 *
86 * Anyway, this needs more thought.... pjsg (1993-08-28)
87 *
88 * If you are really that interested, you should be reading
89 * comp.protocols.time.ntp!
90 */
91
92 static unsigned long get_offset_pit(void)
93 {
94 int count;
95 unsigned long flags;
96 static unsigned long jiffies_p = 0;
97
98 /*
99 * cache volatile jiffies temporarily; we have xtime_lock.
100 */
101 unsigned long jiffies_t;
102
103 spin_lock_irqsave(&i8253_lock, flags);
104 /* timer count may underflow right here */
105 outb_p(0x00, PIT_MODE); /* latch the count ASAP */
106
107 count = inb_p(PIT_CH0); /* read the latched count */
108
109 /*
110 * We do this guaranteed double memory access instead of a _p
111 * postfix in the previous port access. Wheee, hackady hack
112 */
113 jiffies_t = jiffies;
114
115 count |= inb_p(PIT_CH0) << 8;
116
117 /* VIA686a test code... reset the latch if count > max + 1 */
118 if (count > LATCH) {
119 outb_p(0x34, PIT_MODE);
120 outb_p(LATCH & 0xff, PIT_CH0);
121 outb(LATCH >> 8, PIT_CH0);
122 count = LATCH - 1;
123 }
124
125 /*
126 * avoiding timer inconsistencies (they are rare, but they happen)...
127 * there are two kinds of problems that must be avoided here:
128 * 1. the timer counter underflows
129 * 2. hardware problem with the timer, not giving us continuous time,
130 * the counter does small "jumps" upwards on some Pentium systems,
131 * (see c't 95/10 page 335 for Neptun bug.)
132 */
133
134 if( jiffies_t == jiffies_p ) {
135 if( count > count_p ) {
136 /* the nutcase */
137 count = do_timer_overflow(count);
138 }
139 } else
140 jiffies_p = jiffies_t;
141
142 count_p = count;
143
144 spin_unlock_irqrestore(&i8253_lock, flags);
145
146 count = ((LATCH-1) - count) * TICK_SIZE;
147 count = (count + LATCH/2) / LATCH;
148
149 return count;
150 }
151
152
153 /* tsc timer_opts struct */
154 struct timer_opts timer_pit = {
155 .name = "pit",
156 .mark_offset = mark_offset_pit,
157 .get_offset = get_offset_pit,
158 .monotonic_clock = monotonic_clock_pit,
159 .delay = delay_pit,
160 };
161
162 struct init_timer_opts __initdata timer_pit_init = {
163 .init = init_pit,
164 .opts = &timer_pit,
165 };
166
167 void setup_pit_timer(void)
168 {
169 extern spinlock_t i8253_lock;
170 unsigned long flags;
171
172 spin_lock_irqsave(&i8253_lock, flags);
173 outb_p(0x34,PIT_MODE); /* binary, mode 2, LSB/MSB, ch 0 */
174 udelay(10);
175 outb_p(LATCH & 0xff , PIT_CH0); /* LSB */
176 udelay(10);
177 outb(LATCH >> 8 , PIT_CH0); /* MSB */
178 spin_unlock_irqrestore(&i8253_lock, flags);
179 }
180
181 static int timer_resume(struct sys_device *dev)
182 {
183 setup_pit_timer();
184 return 0;
185 }
186
187 static struct sysdev_class timer_sysclass = {
188 set_kset_name("timer_pit"),
189 .resume = timer_resume,
190 };
191
192 static struct sys_device device_timer = {
193 .id = 0,
194 .cls = &timer_sysclass,
195 };
196
197 static int __init init_timer_sysfs(void)
198 {
199 int error = sysdev_class_register(&timer_sysclass);
200 if (!error)
201 error = sysdev_register(&device_timer);
202 return error;
203 }
204
205 device_initcall(init_timer_sysfs);
206
207
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