Bring in the time reference for the x86 platforms

This code uses the always (hopefully) existing PIT device to get the time
reference for barebox.

Signed-off-by: Juergen Beisert <jbe@pengutronix.de>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

2 files changed, 74 insertions, 0 deletions

diff --git a/arch/x86/mach-i386/Makefile b/arch/x86/mach-i386/Makefile
index 49ed10ff54..10712e6a3b 100644
--- a/arch/x86/mach-i386/Makefile
+++ b/arch/x86/mach-i386/Makefile
@@ -1,2 +1,5 @@
 obj-y += generic.o
 obj-y += reset.o
+
+# reference clocksource
+obj-y += pit_timer.o
diff --git a/arch/x86/mach-i386/pit_timer.c b/arch/x86/mach-i386/pit_timer.c
new file mode 100644
index 0000000000..b9f805e61f
--- /dev/null
+++ b/arch/x86/mach-i386/pit_timer.c
@@ -0,0 +1,71 @@
+/*
+ * Copyright (C) 2009 Juergen Beisert, Pengutronix
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License as
+ * published by the Free Software Foundation; either version 2 of
+ * the License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place, Suite 330, Boston,
+ * MA 02111-1307 USA
+ *
+ */
+
+/**
+ * @file
+ * @brief Clocksource based on the 'Programmable Interval Timer' PIT (8253)
+ *
+ * This timer should be available on almost all PCs. It also should be run
+ * at a fixed frequency (1193181.8181 Hz) and not modified to use another
+ * reload value than 0xFFFF. So, it always counts from 0xffff down to 0.
+ *
+ * @note: We can't reprogram the PIT, it will be still used by the BIOS. This
+ * clocksource driver does not touch any PIT settings.
+ */
+
+#include <init.h>
+#include <clock.h>
+#include <asm/io.h>
+
+/** base address of the PIT in a standard PC */
+#define PIT 0x40
+
+static uint64_t pit_clocksource_read(void)
+{
+	uint16_t val1, val2;
+
+	outb(0x00, PIT + 3);	/* latch counter 0 */
+	outb(0x00, 0x80);
+
+	val1 = inb(PIT);
+	outb(0x00, 0x80);
+
+	val2 = inb(PIT);
+	val2 <<= 8;
+
+	/* note: its a down counter */
+	return 0xFFFFU - (val1 | val2);
+}
+
+static struct clocksource cs = {
+	.read	= pit_clocksource_read,
+	.mask	= 0x0000ffff,
+	.shift	= 10,
+};
+
+static int clocksource_init (void)
+{
+	cs.mult = clocksource_hz2mult(1193182, cs.shift);
+	init_clock(&cs);
+
+	return 0;
+}
+
+core_initcall(clocksource_init);