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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/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 enter_contest(u64 mark, long add)
- {
- while (get_tb() < mark)
- tbsync->race_result = add;
- }
- void 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 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 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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