x86/platform: Add a wallclock_init func to x86_init.timers ops

Some wall clock devices use MMIO based HW register, this new
function will give them a chance to do some initialization work
before their get/set_time service get called, which is usually
in early kernel boot phase.
Signed-off-by: NFeng Tang <feng.tang@intel.com>
Signed-off-by: NJacob Pan <jacob.jun.pan@linux.intel.com>
Signed-off-by: NAlan Cox <alan@linux.intel.com>
Signed-off-by: NThomas Gleixner <tglx@linutronix.de>

arch/x86/include/asm/x86_init.h

@@ -83,11 +83,13 @@ struct x86_init_paging {
  *				boot cpu
  * @tsc_pre_init:		platform function called before TSC init
  * @timer_init:			initialize the platform timer (default PIT/HPET)
+ * @wallclock_init:		init the wallclock device
  */
 struct x86_init_timers {
 	void (*setup_percpu_clockev)(void);
 	void (*tsc_pre_init)(void);
 	void (*timer_init)(void);
+	void (*wallclock_init)(void);
 };
 
 /**

arch/x86/kernel/setup.c

@@ -1059,6 +1059,8 @@ void __init setup_arch(char **cmdline_p)
 #endif
 	x86_init.oem.banner();
 
+	x86_init.timers.wallclock_init();
+
 	mcheck_init();
 
 	local_irq_save(flags);

arch/x86/kernel/x86_init.c

@@ -70,6 +70,7 @@ struct x86_init_ops x86_init __initdata = {
 		.setup_percpu_clockev	= setup_boot_APIC_clock,
 		.tsc_pre_init		= x86_init_noop,
 		.timer_init		= hpet_time_init,
+		.wallclock_init		= x86_init_noop,
 	},
 
 	.iommu = {