This patch implements support for a different timing source for the i386
architecture, the Power Management Timer (PMTMR). It offers correct results
with a ~3.6MHz resolution even during aggressive Powermanagement like ACPI
C-State transitions, throttling and/or frequency scaling. It is based partly
on Arjan's patch for 2.4.
arch/i386/Kconfig | 10 +
arch/i386/kernel/time.c | 1
arch/i386/kernel/timers/Makefile | 1
arch/i386/kernel/timers/timer_pm.c | 188 +++++++++++++++++++++++++++++++++++++
4 files changed, 200 insertions(+)
diff -ruN linux-original/arch/i386/Kconfig linux/arch/i386/Kconfig
--- linux-original/arch/i386/Kconfig 2003-07-14 17:13:27.000000000 +0200
+++ linux/arch/i386/Kconfig 2003-07-19 09:42:33.000000000 +0200
@@ -506,6 +506,16 @@
depends on (MWINCHIP3D || MWINCHIP2 || MCRUSOE || MCYRIXIII || MK7 || MK6 || MPENTIUM4 || MPENTIUMIII || MPENTIUMII || M686 || M586MMX || M586TSC || MK8 || MVIAC3_2) && !X86_NUMAQ
default y
+config X86_PM_TIMER
+ tristate "Use Power Management Timer (PMTMR) as primary timing source"
+ depends on ACPI_BUS
+ help
+ The Power Management Timer (PMTMR) is available on all
+ ACPI-capable systems. it provides a reliable timing source
+ which does not get affected by powermanagement features
+ (e.g. aggressive idling, throttling or frequency scaling),
+ unlike the commonly used Time Stamp Counter (TSC) timing source.
+
config X86_MCE
bool "Machine Check Exception"
---help---
diff -ruN linux-original/arch/i386/kernel/time.c linux/arch/i386/kernel/time.c
--- linux-original/arch/i386/kernel/time.c 2003-07-14 17:13:27.000000000 +0200
+++ linux/arch/i386/kernel/time.c 2003-07-18 17:50:12.000000000 +0200
@@ -81,6 +81,7 @@
EXPORT_SYMBOL(i8253_lock);
struct timer_opts *cur_timer = &timer_none;
+EXPORT_SYMBOL(cur_timer);
/*
* This version of gettimeofday has microsecond resolution
diff -ruN linux-original/arch/i386/kernel/timers/Makefile linux/arch/i386/kernel/timers/Makefile
--- linux-original/arch/i386/kernel/timers/Makefile 2003-06-15 12:16:15.000000000 +0200
+++ linux/arch/i386/kernel/timers/Makefile 2003-07-19 09:22:39.000000000 +0200
@@ -5,3 +5,4 @@
obj-y := timer.o timer_none.o timer_tsc.o timer_pit.o
obj-$(CONFIG_X86_CYCLONE_TIMER) += timer_cyclone.o
+obj-$(CONFIG_X86_PM_TIMER) += timer_pm.o
diff -ruN linux-original/arch/i386/kernel/timers/timer_pm.c linux/arch/i386/kernel/timers/timer_pm.c
--- linux-original/arch/i386/kernel/timers/timer_pm.c 1970-01-01 01:00:00.000000000 +0100
+++ linux/arch/i386/kernel/timers/timer_pm.c 2003-07-19 09:50:57.000000000 +0200
@@ -0,0 +1,188 @@
+/*
+ * (C) Dominik Brodowski <linux@brodo.de> 2003
+ *
+ * Driver to use the Power Management Timer (PMTMR) available in some
+ * southbridges as primary timing source for the Linux kernel.
+ *
+ * based on parts of linux/drivers/acpi/hardware/hwtimer.c and of timer_pit.c,
+ * and on Arjan van de Ven's implementation for 2.4.
+ *
+ * This file is licensed under the GPL v2.
+ */
+
+
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/device.h>
+#include <linux/init.h>
+#include <asm/types.h>
+#include <asm/timer.h>
+#include <asm/smp.h>
+#include <asm/io.h>
+#include <asm/arch_hooks.h>
+
+/* The I/O port the PMTMR resides at */
+static u32 pmtmr_ioport = 0;
+
+/* value of the Power timer at last timer interrupt */
+static u32 offset_tick;
+
+/* forward declaration of our timer_opts struct */
+struct timer_opts timer_pmtmr;
+static void mark_offset_pmtmr(void);
+
+/************ detection of the I/O port *****************/
+
+/*
+ * The PMTMR I/O port can be detected using the following methods:
+ *
+ * a) Scan the PCI bus for the device the PMTMR is located at [e.g. PIIX4 southbridge],
+ * locate its I/O port range, and then use a table-lookup to find the I/O port
+ * (offset) for the PMTMR for this device.
+ * While this provides some safety from buggy BIOSes, it is also very chipset-specific
+ * and only available once the PCI devices are properly enabled, e.g. very late during
+ * the boot process. Another timing source needs to be used in between. However, as this
+ * approach is independent of ACPI and CONFIG_ACPI, it might be a good solution for some
+ * very broken systems.
+ * This method is not implemented yet.
+ *
+ * b) Ask the ACPI subsystem's FADT. While this is the easiest approach, it also means that
+ * this timer is only available _late_ in the boot process, only after the ACPI subsystem
+ * has been initialized (which is a subsys_initcall). However, the timing sources are set
+ * up already earlier. This means that we need to use the TSC or the PIT intermediately until
+ * this code replaces the earlier used timer with the PMTMR [see mark_offset_and_replace() foir
+ * details on this].
+ * This method is implemented.
+ *
+ * c) Parse the ACPI FADT here, too. This means that this code could be independend of CONFIG_ACPI,
+ * but it would cause a lot of code duplication between the ACPI subsystem and this file. However,
+ * as this could mean that the PMTMR can be used immediately, without having to rely on alternate
+ * timing sources first.
+ * This method is not implemented yet.
+ */
+
+static void mark_offset_and_replace(void)
+{
+ cur_timer = &timer_pmtmr;
+ mark_offset_pmtmr();
+}
+
+/* method b) */
+
+#include <acpi/acpi.h>
+#include <acpi/acpi_bus.h>
+
+struct timer_opts *prev_timer;
+
+static int __init pmtimer_init(void)
+{
+ int ret;
+
+ ret = acpi_get_timer(&offset_tick);
+ if (ret) {
+ printk(KERN_ERR "acpi_get_timer failed\n");
+ return -EINVAL;
+ }
+
+ if (acpi_fadt.xpm_tmr_blk.address_space_id != ACPI_ADR_SPACE_SYSTEM_IO) {
+ printk(KERN_INFO "ACPI PM timer is not at IO port -- error\n");
+ return -EINVAL;
+ }
+
+ pmtmr_ioport = acpi_fadt.xpm_tmr_blk.address;
+ if (!pmtmr_ioport) {
+ printk(KERN_INFO "ACPI PM timer invalid IO port\n");
+ return -EINVAL;
+ }
+
+ printk(KERN_INFO "Using ACPI PM timer at 0x%x as timing source.\n", pmtmr_ioport);
+
+ prev_timer = cur_timer;
+ cur_timer->mark_offset = mark_offset_and_replace;
+
+ return 0;
+}
+fs_initcall(pmtimer_init);
+
+static void __exit pmtimer_exit(void)
+{
+ cur_timer = prev_timer;
+}
+module_exit(pmtimer_exit);
+
+
+/************ actual timing code *****************/
+
+/*
+ * this gets called during each timer interrupt
+ */
+static void mark_offset_pmtmr(void)
+{
+ offset_tick = inl(pmtmr_ioport);
+ offset_tick &= 0xFFFFFF; /* limit it to 24 bits */
+ return;
+}
+
+/*
+ * would it be desirable to have a ~279 nanosecond resolution?
+ */
+static unsigned long long monotonic_clock_pmtmr(void)
+{
+ return 0;
+}
+
+/*
+ * copied from delay_pit
+ */
+static void delay_pmtmr(unsigned long loops)
+{
+ int d0;
+ __asm__ __volatile__(
+ "\tjmp 1f\n"
+ ".align 16\n"
+ "1:\tjmp 2f\n"
+ ".align 16\n"
+ "2:\tdecl %0\n\tjns 2b"
+ :"=&a" (d0)
+ :"0" (loops));
+}
+
+/*
+ * get the offset (in microseconds) from the last call to mark_offset()
+ */
+static unsigned long get_offset_pmtmr(void)
+{
+ u32 now, offset, delta = 0;
+
+ offset = offset_tick;
+ now = inl(pmtmr_ioport);
+ now &= 0xFFFFFF;
+ if (offset < now)
+ delta = now - offset;
+ else if (offset > now)
+ delta = (0xFFFFFF - offset) + now;
+
+ /* The Power Management Timer ticks at 3.579545 ticks per microsecond.
+ * 1 / PM_TIMER_FREQUENCY == 0.27936511 =~ 286/1024 [error: 0.024%]
+ *
+ * Even with HZ = 100, delta is at maximum 35796 ticks, so it can
+ * easily be multiplied with 286 (=0x11E) without having to fear
+ * u32 overflows.
+ */
+ delta *= 286;
+ return (unsigned long) (delta >> 10);
+}
+
+/* acpi timer_opts struct */
+struct timer_opts timer_pmtmr = {
+ .init = NULL,
+ .mark_offset = mark_offset_pmtmr,
+ .get_offset = get_offset_pmtmr,
+ .monotonic_clock = monotonic_clock_pmtmr,
+ .delay = delay_pmtmr,
+};
+
+
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR("Dominik Brodowski <linux@brodo.de>");
+MODULE_DESCRIPTION("Power Management Timer (PMTMR) as primary timing source for i386");
-
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This archive was generated by hypermail 2b29 : Wed Jul 23 2003 - 22:00:37 EST