rtc: use the IRQ callback interface in (old) RTC driver

the previous patch in the old RTC driver.  It also removes the direct
rtc_interrupt() call from arch/x86/kernel/hpetc.c so that there's finally no
(code) dependency to CONFIG_RTC in arch/x86/kernel/hpet.c.

Because of this, it's possible to compile the drivers/char/rtc.ko driver as
module and still use the HPET emulation functionality.  This is also expressed
in Kconfig.
Signed-off-by: Bernhard Walle <bwalle@suse.de>
Cc: Alessandro Zummo <a.zummo@towertech.it>
Cc: David Brownell <david-b@pacbell.net>
Cc: Andi Kleen <ak@suse.de>
Cc: john stultz <johnstul@us.ibm.com>
Cc: Robert Picco <Robert.Picco@hp.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

arch/x86/Kconfig

@@ -390,7 +390,7 @@ config HPET_TIMER
 
 config HPET_EMULATE_RTC
 	def_bool y
-	depends on HPET_TIMER && RTC=y
+	depends on HPET_TIMER && (RTC=y || RTC=m)
 
 # Mark as embedded because too many people got it wrong.
 # The code disables itself when not needed.

arch/x86/kernel/hpet.c

@@ -705,8 +705,6 @@ irqreturn_t hpet_rtc_interrupt(int irq, void *dev_id)
 		rtc_int_flag |= (RTC_IRQF | (RTC_NUM_INTS << 8));
 		if (irq_handler)
 			irq_handler(rtc_int_flag, dev_id);
-
-		rtc_interrupt(rtc_int_flag, dev_id);
 	}
 	return IRQ_HANDLED;
 }

drivers/char/rtc.c

@@ -110,6 +110,8 @@ static int rtc_has_irq = 1;
 #define hpet_set_rtc_irq_bit(arg)		0
 #define hpet_rtc_timer_init()			do { } while (0)
 #define hpet_rtc_dropped_irq()			0
+#define hpet_register_irq_handler(h)		0
+#define hpet_unregister_irq_handler(h)		0
 #ifdef RTC_IRQ
 static irqreturn_t hpet_rtc_interrupt(int irq, void *dev_id)
 {
@@ -1027,7 +1029,15 @@ static int __init rtc_init(void)
 
 #ifdef RTC_IRQ
 	if (is_hpet_enabled()) {
+		int err;
+
 		rtc_int_handler_ptr = hpet_rtc_interrupt;
+		err = hpet_register_irq_handler(rtc_interrupt);
+		if (err != 0) {
+			printk(KERN_WARNING "hpet_register_irq_handler failed "
+					"in rtc_init().");
+			return err;
+		}
 	} else {
 		rtc_int_handler_ptr = rtc_interrupt;
 	}
@@ -1050,6 +1060,7 @@ static int __init rtc_init(void)
 	if (misc_register(&rtc_dev)) {
 #ifdef RTC_IRQ
 		free_irq(RTC_IRQ, NULL);
+		hpet_unregister_irq_handler(rtc_interrupt);
 		rtc_has_irq = 0;
 #endif
 		rtc_release_region();
@@ -1141,8 +1152,10 @@ static void __exit rtc_exit(void)
 #else
 	rtc_release_region();
 #ifdef RTC_IRQ
-	if (rtc_has_irq)
+	if (rtc_has_irq) {
 		free_irq(RTC_IRQ, NULL);
+		hpet_unregister_irq_handler(hpet_rtc_interrupt);
+	}
 #endif
 #endif /* CONFIG_SPARC32 */
 }