[PATCH] clocksource init adjustments (fix bug #7426)

This patch resolves the issue found here:
http://bugme.osdl.org/show_bug.cgi?id=7426

The basic summary is:
Currently we register most of i386/x86_64 clocksources at module_init
time. Then we enable clocksource selection at late_initcall time. This
causes some problems for drivers that use gettimeofday for init
calibration routines (specifically the es1968 driver in this case),
where durring module_init, the only clocksource available is the low-res
jiffies clocksource. This may cause slight calibration errors, due to
the small sampling time used.

It should be noted that drivers that require fine grained time may not
function on architectures that do not have better then jiffies
resolution timekeeping (there are a few). However, this does not
discount the reasonable need for such fine-grained timekeeping at init
time.

Thus the solution here is to register clocksources earlier (ideally when
the hardware is being initialized), and then we enable clocksource
selection at fs_initcall (before device_initcall).

This patch should probably get some testing time in -mm, since
clocksource selection is one of the most important issues for correct
timekeeping, and I've only been able to test this on a few of my own
boxes.

Signed-off-by: John Stultz <johnstul@us.ibm.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: "David S. Miller" <davem@davemloft.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 37 insertions, 43 deletions

diff --git a/arch/i386/kernel/hpet.c b/arch/i386/kernel/hpet.c
index e1006b7acc9e..f3ab61ee7498 100644
--- a/arch/i386/kernel/hpet.c
+++ b/arch/i386/kernel/hpet.c
@@ -201,12 +201,30 @@ static int hpet_next_event(unsigned long delta,
 }
 
 /*
+ * Clock source related code
+ */
+static cycle_t read_hpet(void)
+{
+        return (cycle_t)hpet_readl(HPET_COUNTER);
+}
+
+static struct clocksource clocksource_hpet = {
+        .name           = "hpet",
+        .rating         = 250,
+        .read           = read_hpet,
+        .mask           = HPET_MASK,
+        .shift          = HPET_SHIFT,
+        .flags          = CLOCK_SOURCE_IS_CONTINUOUS,
+};
+
+/*
  * Try to setup the HPET timer
  */
 int __init hpet_enable(void)
 {
         unsigned long id;
         uint64_t hpet_freq;
+        u64 tmp;
 
         if (!is_hpet_capable())
                 return 0;
@@ -253,6 +271,25 @@ int __init hpet_enable(void)
         /* Start the counter */
         hpet_start_counter();
 
+        /* Initialize and register HPET clocksource
+         *
+         * hpet period is in femto seconds per cycle
+         * so we need to convert this to ns/cyc units
+         * aproximated by mult/2^shift
+         *
+         *  fsec/cyc * 1nsec/1000000fsec = nsec/cyc = mult/2^shift
+         *  fsec/cyc * 1ns/1000000fsec * 2^shift = mult
+         *  fsec/cyc * 2^shift * 1nsec/1000000fsec = mult
+         *  (fsec/cyc << shift)/1000000 = mult
+         *  (hpet_period << shift)/FSEC_PER_NSEC = mult
+         */
+        tmp = (u64)hpet_period << HPET_SHIFT;
+        do_div(tmp, FSEC_PER_NSEC);
+        clocksource_hpet.mult = (u32)tmp;
+
+        clocksource_register(&clocksource_hpet);
+
+
         if (id & HPET_ID_LEGSUP) {
                 hpet_enable_int();
                 hpet_reserve_platform_timers(id);
@@ -273,49 +310,6 @@ out_nohpet:
         return 0;
 }
 
-/*
- * Clock source related code
- */
-static cycle_t read_hpet(void)
-{
-        return (cycle_t)hpet_readl(HPET_COUNTER);
-}
-
-static struct clocksource clocksource_hpet = {
-        .name           = "hpet",
-        .rating         = 250,
-        .read           = read_hpet,
-        .mask           = HPET_MASK,
-        .shift          = HPET_SHIFT,
-        .flags          = CLOCK_SOURCE_IS_CONTINUOUS,
-};
-
-static int __init init_hpet_clocksource(void)
-{
-        u64 tmp;
-
-        if (!hpet_virt_address)
-                return -ENODEV;
-
-        /*
-         * hpet period is in femto seconds per cycle
-         * so we need to convert this to ns/cyc units
-         * aproximated by mult/2^shift
-         *
-         *  fsec/cyc * 1nsec/1000000fsec = nsec/cyc = mult/2^shift
-         *  fsec/cyc * 1ns/1000000fsec * 2^shift = mult
-         *  fsec/cyc * 2^shift * 1nsec/1000000fsec = mult
-         *  (fsec/cyc << shift)/1000000 = mult
-         *  (hpet_period << shift)/FSEC_PER_NSEC = mult
-         */
-        tmp = (u64)hpet_period << HPET_SHIFT;
-        do_div(tmp, FSEC_PER_NSEC);
-        clocksource_hpet.mult = (u32)tmp;
-
-        return clocksource_register(&clocksource_hpet);
-}
-
-module_init(init_hpet_clocksource);
 
 #ifdef CONFIG_HPET_EMULATE_RTC