[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, 46 deletions

diff --git a/arch/i386/kernel/tsc.c b/arch/i386/kernel/tsc.c
index 59222a04234b..875d8a6ecc02 100644
--- a/arch/i386/kernel/tsc.c
+++ b/arch/i386/kernel/tsc.c
@@ -184,34 +184,6 @@ int recalibrate_cpu_khz(void)
 
 EXPORT_SYMBOL(recalibrate_cpu_khz);
 
-void __init tsc_init(void)
-{
-        if (!cpu_has_tsc || tsc_disable)
-                goto out_no_tsc;
-
-        cpu_khz = calculate_cpu_khz();
-        tsc_khz = cpu_khz;
-
-        if (!cpu_khz)
-                goto out_no_tsc;
-
-        printk("Detected %lu.%03lu MHz processor.\n",
-                                (unsigned long)cpu_khz / 1000,
-                                (unsigned long)cpu_khz % 1000);
-
-        set_cyc2ns_scale(cpu_khz);
-        use_tsc_delay();
-        return;
-
-out_no_tsc:
-        /*
-         * Set the tsc_disable flag if there's no TSC support, this
-         * makes it a fast flag for the kernel to see whether it
-         * should be using the TSC.
-         */
-        tsc_disable = 1;
-}
-
 #ifdef CONFIG_CPU_FREQ
 
 /*
@@ -381,28 +353,47 @@ static void __init check_geode_tsc_reliable(void)
 static inline void check_geode_tsc_reliable(void) { }
 #endif
 
-static int __init init_tsc_clocksource(void)
+
+void __init tsc_init(void)
 {
+        if (!cpu_has_tsc || tsc_disable)
+                goto out_no_tsc;
 
-        if (cpu_has_tsc && tsc_khz && !tsc_disable) {
-                /* check blacklist */
-                dmi_check_system(bad_tsc_dmi_table);
+        cpu_khz = calculate_cpu_khz();
+        tsc_khz = cpu_khz;
 
-                unsynchronized_tsc();
-                check_geode_tsc_reliable();
-                current_tsc_khz = tsc_khz;
-                clocksource_tsc.mult = clocksource_khz2mult(current_tsc_khz,
-                                                        clocksource_tsc.shift);
-                /* lower the rating if we already know its unstable: */
-                if (check_tsc_unstable()) {
-                        clocksource_tsc.rating = 0;
-                        clocksource_tsc.flags &= ~CLOCK_SOURCE_IS_CONTINUOUS;
-                }
+        if (!cpu_khz)
+                goto out_no_tsc;
 
-                return clocksource_register(&clocksource_tsc);
+        printk("Detected %lu.%03lu MHz processor.\n",
+                                (unsigned long)cpu_khz / 1000,
+                                (unsigned long)cpu_khz % 1000);
+
+        set_cyc2ns_scale(cpu_khz);
+        use_tsc_delay();
+
+        /* Check and install the TSC clocksource */
+        dmi_check_system(bad_tsc_dmi_table);
+
+        unsynchronized_tsc();
+        check_geode_tsc_reliable();
+        current_tsc_khz = tsc_khz;
+        clocksource_tsc.mult = clocksource_khz2mult(current_tsc_khz,
+                                                        clocksource_tsc.shift);
+        /* lower the rating if we already know its unstable: */
+        if (check_tsc_unstable()) {
+                clocksource_tsc.rating = 0;
+                clocksource_tsc.flags &= ~CLOCK_SOURCE_IS_CONTINUOUS;
         }
+        clocksource_register(&clocksource_tsc);
 
-        return 0;
-}
+        return;
 
-module_init(init_tsc_clocksource);
+out_no_tsc:
+        /*
+         * Set the tsc_disable flag if there's no TSC support, this
+         * makes it a fast flag for the kernel to see whether it
+         * should be using the TSC.
+         */
+        tsc_disable = 1;
+}