cpufreq: acpi-cpufreq: Clean up hot plug notifier callback

This driver has two issues.  First, it tries to fiddle with the hot
plugged CPU's MSR on the UP_PREPARE event, at a time when the CPU is
not yet online.  Second, the driver sets the "boost-disable" bit for a
CPU when going down, but does not clear the bit again if the CPU comes
up again due to DOWN_FAILED.

This patch fixes the issues by changing the driver to react to the
ONLINE/DOWN_FAILED events instead of UP_PREPARE.  As an added benefit,
the driver also becomes symmetric with respect to the hot plug
mechanism.
Signed-off-by: Richard Cochran <rcochran@linutronix.de>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

drivers/cpufreq/acpi-cpufreq.c

@@ -514,8 +514,10 @@ static int boost_notify(struct notifier_block *nb, unsigned long action,
 	 */
 
 	switch (action) {
-	case CPU_UP_PREPARE:
-	case CPU_UP_PREPARE_FROZEN:
+	case CPU_DOWN_FAILED:
+	case CPU_DOWN_FAILED_FROZEN:
+	case CPU_ONLINE:
+	case CPU_ONLINE_FROZEN:
 		boost_set_msrs(acpi_cpufreq_driver.boost_enabled, cpumask);
 		break;