/* * 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 <asm/atomic.h> #include <asm/smp.h> #include <asm/time.h> #define NUM_ITER 300 enum { kExit=0, kSetAndTest, kTest }; static struct { volatile int tbu; volatile int tbl; volatile int 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( int mark, int add ) { while( (int)(get_tbl() - mark) < 0 ) tbsync->race_result = add; } void __devinit smp_generic_take_timebase( void ) { int cmd, tbl, tbu; unsigned long flags; local_irq_save(flags); while( !running ) ; rmb(); for( ;; ) { tbsync->ack = 1; while( !tbsync->handshake ) ; rmb(); cmd = tbsync->cmd; tbl = tbsync->tbl; tbu = tbsync->tbu; tbsync->ack = 0; if( cmd == kExit ) break; if( cmd == kSetAndTest ) { while( tbsync->handshake ) ; asm volatile ("mttbl %0" :: "r" (tbl) ); asm volatile ("mttbu %0" :: "r" (tbu) ); } else { while( tbsync->handshake ) ; } enter_contest( tbsync->mark, -1 ); } local_irq_restore(flags); } static int __devinit start_contest( int cmd, int offset, int num ) { int i, tbu, tbl, mark, score=0; tbsync->cmd = cmd; local_irq_disable(); for( i=-3; i<num; ) { tbl = get_tbl() + 400; tbsync->tbu = tbu = get_tbu(); tbsync->tbl = tbl + offset; tbsync->mark = mark = tbl + 400; wmb(); tbsync->handshake = 1; while( tbsync->ack ) ; while( (int)(get_tbl() - tbl) <= 0 ) ; tbsync->handshake = 0; enter_contest( mark, 1 ); while( !tbsync->ack ) ; if( tbsync->tbu != get_tbu() || ((tbsync->tbl ^ get_tbl()) & 0x80000000) ) 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 = kzalloc( sizeof(*tbsync), GFP_KERNEL ); mb(); running = 1; while( !tbsync->ack ) ; /* 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; /* all done */ smp_tb_synchronized = 1; }