From 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 Mon Sep 17 00:00:00 2001
From: Linus Torvalds <torvalds@ppc970.osdl.org>
Date: Sat, 16 Apr 2005 15:20:36 -0700
Subject: Linux-2.6.12-rc2

Initial git repository build. I'm not bothering with the full history,
even though we have it. We can create a separate "historical" git
archive of that later if we want to, and in the meantime it's about
3.2GB when imported into git - space that would just make the early
git days unnecessarily complicated, when we don't have a lot of good
infrastructure for it.

Let it rip!
---
 arch/ppc/kernel/smp-tbsync.c | 181 +++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 181 insertions(+)
 create mode 100644 arch/ppc/kernel/smp-tbsync.c

(limited to 'arch/ppc/kernel/smp-tbsync.c')

diff --git a/arch/ppc/kernel/smp-tbsync.c b/arch/ppc/kernel/smp-tbsync.c
new file mode 100644
index 00000000000..2c9cd95bcea
--- /dev/null
+++ b/arch/ppc/kernel/smp-tbsync.c
@@ -0,0 +1,181 @@
+/*
+ * 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 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;
+
+	local_irq_disable();
+	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 )
+			return;
+
+		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_enable();
+}
+
+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 = kmalloc( sizeof(*tbsync), GFP_KERNEL );
+	memset( tbsync, 0, sizeof(*tbsync) );
+	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;
+}
-- 
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