Commit 6ae7440e authored by Jim Cromie's avatar Jim Cromie Committed by Linus Torvalds
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[PATCH] GTOD: add scx200 HRT clocksource

Add a GTOD clocksource driver based on the Geode SCx200's Hi-Res Timer.
Signed-off-by: default avatarJim Cromie <>
Cc: Roman Zippel <>
Cc: john stultz <>
Signed-off-by: default avatarAndrew Morton <>
Signed-off-by: default avatarLinus Torvalds <>
parent 19923c19
......@@ -1050,13 +1050,23 @@ config SCx200
tristate "NatSemi SCx200 support"
depends on !X86_VOYAGER
This provides basic support for the National Semiconductor SCx200
processor. Right now this is just a driver for the GPIO pins.
This provides basic support for National Semiconductor's
(now AMD's) Geode processors. The driver probes for the
PCI-IDs of several on-chip devices, so its a good dependency
for other scx200_* drivers.
If you don't know what to do here, say N.
If compiled as a module, the driver is named scx200.
This support is also available as a module. If compiled as a
module, it will be called scx200.
config SCx200HR_TIMER
tristate "NatSemi SCx200 27MHz High-Resolution Timer Support"
depends on SCx200 && GENERIC_TIME
default y
This driver provides a clocksource built upon the on-chip
27MHz high-resolution timer. Its also a workaround for
NSC Geode SC-1100's buggy TSC, which loses time when the
processor goes idle (as is done by the scheduler). The
other workaround is idle=poll boot option.
source "drivers/pcmcia/Kconfig"
obj-$(CONFIG_X86_CYCLONE_TIMER) += cyclone.o
obj-$(CONFIG_X86_PM_TIMER) += acpi_pm.o
obj-$(CONFIG_X86_CYCLONE_TIMER) += cyclone.o
obj-$(CONFIG_X86_PM_TIMER) += acpi_pm.o
obj-$(CONFIG_SCx200HR_TIMER) += scx200_hrt.o
* Copyright (C) 2006 Jim Cromie
* This is a clocksource driver for the Geode SCx200's 1 or 27 MHz
* high-resolution timer. The Geode SC-1100 (at least) has a buggy
* time stamp counter (TSC), which loses time unless 'idle=poll' is
* given as a boot-arg. In its absence, the Generic Timekeeping code
* will detect and de-rate the bad TSC, allowing this timer to take
* over timekeeping duties.
* Based on work by John Stultz, and Ted Phelps (in a 2.6.12-rc6 patch)
* 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.
#include <linux/clocksource.h>
#include <linux/init.h>
#include <linux/module.h>
#include <linux/ioport.h>
#include <linux/scx200.h>
#define NAME "scx200_hrt"
static int mhz27;
module_param(mhz27, int, 0); /* load time only */
MODULE_PARM_DESC(mhz27, "count at 27.0 MHz (default is 1.0 MHz)");
static int ppm;
module_param(ppm, int, 0); /* load time only */
MODULE_PARM_DESC(ppm, "+-adjust to actual XO freq (ppm)");
/* HiRes Timer configuration register address */
#define SCx200_TMCNFG_OFFSET (SCx200_TIMER_OFFSET + 5)
/* and config settings */
#define HR_TMEN (1 << 0) /* timer interrupt enable */
#define HR_TMCLKSEL (1 << 1) /* 1|0 counts at 27|1 MHz */
#define HR_TM27MPD (1 << 2) /* 1 turns off input clock (power-down) */
/* The base timer frequency, * 27 if selected */
#define HRT_FREQ 1000000
static cycle_t read_hrt(void)
/* Read the timer value */
return (cycle_t) inl(scx200_cb_base + SCx200_TIMER_OFFSET);
#define HRT_SHIFT_1 22
#define HRT_SHIFT_27 26
static struct clocksource cs_hrt = {
.name = "scx200_hrt",
.rating = 250,
.read = read_hrt,
.is_continuous = 1,
/* mult, shift are set based on mhz27 flag */
static int __init init_hrt_clocksource(void)
/* Make sure scx200 has initializedd the configuration block */
if (!scx200_cb_present())
return -ENODEV;
/* Reserve the timer's ISA io-region for ourselves */
if (!request_region(scx200_cb_base + SCx200_TIMER_OFFSET,
"NatSemi SCx200 High-Resolution Timer")) {
printk(KERN_WARNING NAME ": unable to lock timer region\n");
return -ENODEV;
/* write timer config */
outb(HR_TMEN | (mhz27) ? HR_TMCLKSEL : 0,
scx200_cb_base + SCx200_TMCNFG_OFFSET);
if (mhz27) {
cs_hrt.shift = HRT_SHIFT_27;
cs_hrt.mult = clocksource_hz2mult((HRT_FREQ + ppm) * 27,
} else {
cs_hrt.shift = HRT_SHIFT_1;
cs_hrt.mult = clocksource_hz2mult(HRT_FREQ + ppm,
printk(KERN_INFO "enabling scx200 high-res timer (%s MHz +%d ppm)\n",
mhz27 ? "27":"1", ppm);
return clocksource_register(&cs_hrt);
MODULE_AUTHOR("Jim Cromie <>");
MODULE_DESCRIPTION("clocksource on SCx200 HiRes Timer");
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