/* * 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; }