[PATCH] linux-2.5.41_timer-changes_A4 (1/3 - infrastructure)

        The i386 time.c code is turning into a mess. We've got multiple
functions that do the same thing, only with different hardware, all
surrounded #ifdefs and even more difficult to follow #ifndefs. George
Anzinger is introducing a new ACPIpm time source, I'm going to attempt
to add the cyclone counter as a time source, and in the future there
will be HPET to deal with. These will not go in cleanly together as
things are now.

        Inspired by suggestions from Alan, this collection of patches
tries to clean up time.c by breaking out the PIT and TSC specific parts
into their own files. Additionally the patch creates an abstract
interface to use these existing time soruces, as well as make it easier
to add future time sources.

        It introduces "struct timer_ops" which gives the time code a
clear interface to use these different time sources. It also allows for
clearer conditional compilation of these various time sources.

        This first patch (part 1 of 3) provides the infrastructure
needed via the timer_ops structure, as well as the select_timer()
function for choosing the best available timer.

arch/i386/kernel/timers/timer.c

+#include <linux/kernel.h>
+#include <asm/timer.h>
+
+/* list of externed timers */
+/* eg: extern struct timer_opts timer_XXX*/;
+
+/* list of timers, ordered by preference */
+struct timer_opts* timers[] = {
+	/* eg: &timer_XXX */
+};
+
+#define NR_TIMERS (sizeof(timers)/sizeof(timers[0]))
+
+/* iterates through the list of timers, returning the first 
+ * one that initializes successfully.
+ */
+struct timer_opts* select_timer(void)
+{
+	int i;
+	/* find most preferred working timer */
+	for(i=0; i < NR_TIMERS; i++)
+		if(timers[i]->init())
+			return timers[i];
+	panic("select_timer: Cannot find a suitable timer\n");
+	return 0;
+}

include/asm-i386/timer.h

+#ifndef _ASMi386_TIMER_H
+#define _ASMi386_TIMER_H
+
+struct timer_opts{
+	/* probes and initializes timer. returns 1 on sucess, 0 on failure */
+	int (*init)(void);
+	/* called by the timer interrupt */
+	void (*mark_offset)(void);
+	/* called by gettimeofday. returns # ms since the last timer interrupt */
+	unsigned long (*get_offset)(void);
+};
+
+struct timer_opts* select_timer(void);
+#endif