Revert "clocksource: Load the ACPI PM clocksource asynchronously"

This reverts commit b5195082.

The reason for this revert is that making the frequency verification
preemptible and interruptible is not working reliably. Michaels
machine failed to use PM-timer with the message:

  PM-Timer running at invalid rate: 113% of normal - aborting.

That's not a surprise as the frequency verification does rely on
interrupts being disabled. With a async scheduled thread there is no
guarantee to achieve the same result. Also some driver might fiddle
with the CTC channel 2 during the verification period, which makes the
result even more random and unpredictable.

This can be solved by using the same mechanism as we use in the
deferred TSC validation code, but that only will work if we verified a
working HPET _BEFORE_ trying to do the PM-Timer lazy validation.

So for now reverting is the safe option.
Bisected-by: Michael Witten <mfwitten@gmail.com>
Cc: Arjan van de Ven <arjanvandeven@gmail.com>
Cc: Arjan van de Ven <arjan@infradead.org>
Cc: John Stultz <johnstul@us.ibm.com>
Cc: Len Brown <lenb@kernel.org>
LKML-Reference: <alpine.LFD.2.02.1204112303270.2542@ionos>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

drivers/clocksource/acpi_pm.c

@@ -23,7 +23,6 @@
 #include <linux/init.h>
 #include <linux/pci.h>
 #include <linux/delay.h>
-#include <linux/async.h>
 #include <asm/io.h>
 
 /*
@@ -180,15 +179,17 @@ static int verify_pmtmr_rate(void)
 /* Number of reads we try to get two different values */
 #define ACPI_PM_READ_CHECKS 10000
 
-static void __init acpi_pm_clocksource_async(void *unused, async_cookie_t cookie)
+static int __init init_acpi_pm_clocksource(void)
 {
 	cycle_t value1, value2;
 	unsigned int i, j = 0;
 
+	if (!pmtmr_ioport)
+		return -ENODEV;
 
 	/* "verify" this timing source: */
 	for (j = 0; j < ACPI_PM_MONOTONICITY_CHECKS; j++) {
-		usleep_range(100 * j, 100 * j + 100);
+		udelay(100 * j);
 		value1 = clocksource_acpi_pm.read(&clocksource_acpi_pm);
 		for (i = 0; i < ACPI_PM_READ_CHECKS; i++) {
 			value2 = clocksource_acpi_pm.read(&clocksource_acpi_pm);
@@ -202,34 +203,25 @@ static void __init acpi_pm_clocksource_async(void *unused, async_cookie_t cookie
 			       " 0x%#llx, 0x%#llx - aborting.\n",
 			       value1, value2);
 			pmtmr_ioport = 0;
-			return;
+			return -EINVAL;
 		}
 		if (i == ACPI_PM_READ_CHECKS) {
 			printk(KERN_INFO "PM-Timer failed consistency check "
 			       " (0x%#llx) - aborting.\n", value1);
 			pmtmr_ioport = 0;
-			return;
+			return -ENODEV;
 		}
 	}
 
 	if (verify_pmtmr_rate() != 0){
 		pmtmr_ioport = 0;
-		return;
+		return -ENODEV;
 	}
 
-	clocksource_register_hz(&clocksource_acpi_pm,
+	return clocksource_register_hz(&clocksource_acpi_pm,
 						PMTMR_TICKS_PER_SEC);
 }
 
-static int __init init_acpi_pm_clocksource(void)
-{
-	if (!pmtmr_ioport)
-		return -ENODEV;
-
-	async_schedule(acpi_pm_clocksource_async, NULL);
-	return 0;
-}
-
 /* We use fs_initcall because we want the PCI fixups to have run
  * but we still need to load before device_initcall
  */