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/*
* 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;
}
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