clocksource: add unregister function to disable unusable clocksources

On x86 the PIT might become an unusable clocksource. Add an unregister
function to provide a possibilty to remove the PIT from the list of
available clock sources.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 15 insertions, 0 deletions

diff --git a/kernel/time/clocksource.c b/kernel/time/clocksource.c
index edd5ef8e176..6e9259a5d50 100644
--- a/kernel/time/clocksource.c
+++ b/kernel/time/clocksource.c
@@ -337,6 +337,21 @@ void clocksource_change_rating(struct clocksource *cs, int rating)
         spin_unlock_irqrestore(&clocksource_lock, flags);
 }
 
+/**
+ * clocksource_unregister - remove a registered clocksource
+ */
+void clocksource_unregister(struct clocksource *cs)
+{
+        unsigned long flags;
+
+        spin_lock_irqsave(&clocksource_lock, flags);
+        list_del(&cs->list);
+        if (clocksource_override == cs)
+                clocksource_override = NULL;
+        next_clocksource = select_clocksource();
+        spin_unlock_irqrestore(&clocksource_lock, flags);
+}
+
 #ifdef CONFIG_SYSFS
 /**
  * sysfs_show_current_clocksources - sysfs interface for current clocksource