clocksource: Provide clocksource_arch_init()

Architectures have extra archdata in the clocksource, e.g. for VDSO
support. There are no sanity checks or general initializations for this
available. Add support for that.

Signed-off-by: Thomas Gleixner <[e-mail]>
Acked-by: Andy Lutomirski <[e-mail]>
Acked-by: John Stultz <[e-mail]>
Cc: Peter Zijlstra <[e-mail]>
Cc: Matt Rickard <[e-mail]>
Cc: Stephen Boyd <[e-mail]>
Cc: Florian Weimer <[e-mail]>
Cc: "K. Y. Srinivasan" <[e-mail]>
Cc: Vitaly Kuznetsov <[e-mail]>
Cc: [e-mail]
Cc: [e-mail]
Cc: Paolo Bonzini <[e-mail]>
Cc: Arnd Bergmann <[e-mail]>
Cc: Juergen Gross <[e-mail]>
Link: https://lkml.kernel.org/r/[e-mail]

include/linux/clocksource.h

···
 	__clocksource_update_freq_scale(cs, 1000, khz);
 }
 
+#ifdef CONFIG_ARCH_CLOCKSOURCE_INIT
+extern void clocksource_arch_init(struct clocksource *cs);
+#else
+static inline void clocksource_arch_init(struct clocksource *cs) { }
+#endif
 
 extern int timekeeping_notify(struct clocksource *clock);
 

kernel/time/Kconfig

···
 config ARCH_CLOCKSOURCE_DATA
 	bool
 
+# Architecture has extra clocksource init called from registration
+config ARCH_CLOCKSOURCE_INIT
+	bool
+
 # Clocksources require validation of the clocksource against the last
 # cycle update - x86/TSC misfeature
 config CLOCKSOURCE_VALIDATE_LAST_CYCLE

kernel/time/clocksource.c

···
 {
 	unsigned long flags;
 
+	clocksource_arch_init(cs);
+
 	/* Initialize mult/shift and max_idle_ns */
 	__clocksource_update_freq_scale(cs, scale, freq);