summaryrefslogtreecommitdiffstats
path: root/arch/ppc64/kernel/smp-tbsync.c
blob: 7d8ec9996b3e7ea91f4f3dd3ba18a12d616f5a07 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
/*
 * Smp timebase synchronization for ppc.
 *
 * Copyright (C) 2003 Samuel Rydh (samuel@ibrium.se)
 *
 */

#include <linux/config.h>
#include <linux/kernel.h>
#include <linux/sched.h>
#include <linux/smp.h>
#include <linux/unistd.h>
#include <linux/init.h>
#include <asm/atomic.h>
#include <asm/smp.h>
#include <asm/time.h>

#define NUM_ITER		300

enum {
	kExit=0, kSetAndTest, kTest
};

static struct {
	volatile long		tb;
	volatile long		mark;
	volatile int		cmd;
	volatile int		handshake;
	int			filler[3];

	volatile int		ack;
	int			filler2[7];

	volatile int		race_result;
} *tbsync;

static volatile int		running;

static void __devinit
enter_contest( long mark, long add )
{
	while( (long)(mftb() - mark) < 0 )
		tbsync->race_result = add;
}

void __devinit
smp_generic_take_timebase( void )
{
	int cmd;
	long tb;

	local_irq_disable();
	while( !running )
		;
	rmb();

	for( ;; ) {
		tbsync->ack = 1;
		while( !tbsync->handshake )
			;
		rmb();

		cmd = tbsync->cmd;
		tb = tbsync->tb;
		tbsync->ack = 0;
		if( cmd == kExit )
			return;

		if( cmd == kSetAndTest ) {
			while( tbsync->handshake )
				;
			asm volatile ("mttbl %0" :: "r" (tb & 0xfffffffful) );
			asm volatile ("mttbu %0" :: "r" (tb >> 32) );
		} else {
			while( tbsync->handshake )
				;
		}
		enter_contest( tbsync->mark, -1 );
	}
	local_irq_enable();
}

static int __devinit
start_contest( int cmd, long offset, long num )
{
	int i, score=0;
	long tb, mark;

	tbsync->cmd = cmd;

	local_irq_disable();
	for( i=-3; i<num; ) {
		tb = (long)mftb() + 400;
		tbsync->tb = tb + offset;
		tbsync->mark = mark = tb + 400;

		wmb();

		tbsync->handshake = 1;
		while( tbsync->ack )
			;

		while( (long)(mftb() - tb) <= 0 )
			;
		tbsync->handshake = 0;
		enter_contest( mark, 1 );

		while( !tbsync->ack )
			;

	       	if ((tbsync->tb ^ (long)mftb()) & 0x8000000000000000ul)
			continue;
		if( i++ > 0 )
			score += tbsync->race_result;
	}
	local_irq_enable();
	return score;
}

void __devinit
smp_generic_give_timebase( void )
{
	int i, score, score2, old, min=0, max=5000, offset=1000;

	printk("Synchronizing timebase\n");

	/* if this fails then this kernel won't work anyway... */
	tbsync = kmalloc( sizeof(*tbsync), GFP_KERNEL );
	memset( tbsync, 0, sizeof(*tbsync) );
	mb();
	running = 1;

	while( !tbsync->ack )
		;

	printk("Got ack\n");

	/* binary search */
	for( old=-1 ; old != offset ; offset=(min+max)/2 ) {
		score = start_contest( kSetAndTest, offset, NUM_ITER );

		printk("score %d, offset %d\n", score, offset );

		if( score > 0 )
			max = offset;
		else
			min = offset;
		old = offset;
	}
	score = start_contest( kSetAndTest, min, NUM_ITER );
	score2 = start_contest( kSetAndTest, max, NUM_ITER );

	printk( "Min %d (score %d), Max %d (score %d)\n", min, score, max, score2 );
	score = abs( score );
	score2 = abs( score2 );
	offset = (score < score2) ? min : max;

	/* guard against inaccurate mttb */
	for( i=0; i<10; i++ ) {
		start_contest( kSetAndTest, offset, NUM_ITER/10 );

		if( (score2=start_contest(kTest, offset, NUM_ITER)) < 0 )
			score2 = -score2;
		if( score2 <= score || score2 < 20 )
			break;
	}
	printk("Final offset: %d (%d/%d)\n", offset, score2, NUM_ITER );

	/* exiting */
	tbsync->cmd = kExit;
	wmb();
	tbsync->handshake = 1;
	while( tbsync->ack )
		;
	tbsync->handshake = 0;
	kfree( tbsync );
	tbsync = NULL;
	running = 0;
}