1 files changed, 171 insertions, 0 deletions
diff --git a/arch/powerpc/kernel/smp-tbsync.c b/arch/powerpc/kernel/smp-tbsync.c
new file mode 100644
index 0000000000..21c39355b2
--- /dev/null
+++ b/arch/powerpc/kernel/smp-tbsync.c
@@ -0,0 +1,171 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * 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;
+}