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/*
* Smp timebase synchronization for ppc.
*
* Copyright (C) 2003 Samuel Rydh (samuel@ibrium.se)
*
*/
#include <linux/kernel.h>
#include <linux/sched.h>
#include <linux/smp.h>
#include <linux/unistd.h>
#include <linux/init.h>
#include <linux/slab.h>
#include <linux/atomic.h>
#include <asm/smp.h>
#include <asm/time.h>
#define NUM_ITER 300
enum {
kExit=0, kSetAndTest, kTest
};
static struct {
volatile u64 tb;
volatile u64 mark;
volatile int cmd;
volatile int handshake;
int filler[2];
volatile int ack;
int filler2[7];
volatile int race_result;
} *tbsync;
static volatile int running;
static void __devinit enter_contest(u64 mark, long add)
{
while (get_tb() < mark)
tbsync->race_result = add;
}
void __devinit smp_generic_take_timebase(void)
{
int cmd;
u64 tb;
unsigned long flags;
local_irq_save(flags);
while (!running)
barrier();
rmb();
for (;;) {
tbsync->ack = 1;
while (!tbsync->handshake)
barrier();
rmb();
cmd = tbsync->cmd;
tb = tbsync->tb;
mb();
tbsync->ack = 0;
if (cmd == kExit)
break;
while (tbsync->handshake)
barrier();
if (cmd == kSetAndTest)
set_tb(tb >> 32, tb & 0xfffffffful);
enter_contest(tbsync->mark, -1);
}
local_irq_restore(flags);
}
static int __devinit start_contest(int cmd, long offset, int num)
{
int i, score=0;
u64 tb;
u64 mark;
tbsync->cmd = cmd;
local_irq_disable();
for (i = -3; i < num; ) {
tb = get_tb() + 400;
tbsync->tb = tb + offset;
tbsync->mark = mark = tb + 400;
wmb();
tbsync->handshake = 1;
while (tbsync->ack)
barrier();
while (get_tb() <= tb)
barrier();
tbsync->handshake = 0;
enter_contest(mark, 1);
while (!tbsync->ack)
barrier();
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;
pr_debug("Software timebase sync\n");
/* if this fails then this kernel won't work anyway... */
tbsync = kzalloc( sizeof(*tbsync), GFP_KERNEL );
mb();
running = 1;
while (!tbsync->ack)
barrier();
pr_debug("Got ack\n");
/* binary search */
for (old = -1; old != offset ; offset = (min+max) / 2) {
score = start_contest(kSetAndTest, offset, NUM_ITER);
pr_debug("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);
pr_debug("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;
}
pr_debug("Final offset: %d (%d/%d)\n", offset, score2, NUM_ITER );
/* exiting */
tbsync->cmd = kExit;
wmb();
tbsync->handshake = 1;
while (tbsync->ack)
barrier();
tbsync->handshake = 0;
kfree(tbsync);
tbsync = NULL;
running = 0;
}
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