/* * 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 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; 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) barrier(); 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) barrier(); tbsync->handshake = 0; kfree(tbsync); tbsync = NULL; running = 0; }