RTC: Fix up rtc.txt documentation to reflect changes to generic rtc layer

Now that the genric RTC layer handles much of the RTC functionality,
the rtc.txt documentation needs to be updated to remove outdated information.

CC: Thomas Gleixner <tglx@linutronix.de>
CC: Alessandro Zummo <a.zummo@towertech.it>
CC: Marcelo Roberto Jimenez <mroberto@cpti.cetuc.puc-rio.br>
CC: rtc-linux@googlegroups.com
Signed-off-by: John Stultz <john.stultz@linaro.org>

Documentation/rtc.txt

@@ -178,38 +178,29 @@ RTC class framework, but can't be supported by the older driver.
 	setting the longer alarm time and enabling its IRQ using a single
 	request (using the same model as EFI firmware).
 
-    *	RTC_UIE_ON, RTC_UIE_OFF ... if the RTC offers IRQs, it probably
-	also offers update IRQs whenever the "seconds" counter changes.
-	If needed, the RTC framework can emulate this mechanism.
+    *	RTC_UIE_ON, RTC_UIE_OFF ... if the RTC offers IRQs, the RTC framework
+	will emulate this mechanism.
 
-    *	RTC_PIE_ON, RTC_PIE_OFF, RTC_IRQP_SET, RTC_IRQP_READ ... another
-	feature often accessible with an IRQ line is a periodic IRQ, issued
-	at settable frequencies (usually 2^N Hz).
+    *	RTC_PIE_ON, RTC_PIE_OFF, RTC_IRQP_SET, RTC_IRQP_READ ... these icotls
+	are emulated via a kernel hrtimer.
 
 In many cases, the RTC alarm can be a system wake event, used to force
 Linux out of a low power sleep state (or hibernation) back to a fully
 operational state.  For example, a system could enter a deep power saving
 state until it's time to execute some scheduled tasks.
 
-Note that many of these ioctls need not actually be implemented by your
-driver.  The common rtc-dev interface handles many of these nicely if your
-driver returns ENOIOCTLCMD.  Some common examples:
+Note that many of these ioctls are handled by the common rtc-dev interface.
+Some common examples:
 
     *	RTC_RD_TIME, RTC_SET_TIME: the read_time/set_time functions will be
 	called with appropriate values.
 
-    *	RTC_ALM_SET, RTC_ALM_READ, RTC_WKALM_SET, RTC_WKALM_RD: the
-	set_alarm/read_alarm functions will be called.
+    *	RTC_ALM_SET, RTC_ALM_READ, RTC_WKALM_SET, RTC_WKALM_RD: gets or sets
+	the alarm rtc_timer. May call the set_alarm driver function.
 
-    *	RTC_IRQP_SET, RTC_IRQP_READ: the irq_set_freq function will be called
-	to set the frequency while the framework will handle the read for you
-	since the frequency is stored in the irq_freq member of the rtc_device
-	structure.  Your driver needs to initialize the irq_freq member during
-	init.  Make sure you check the requested frequency is in range of your
-	hardware in the irq_set_freq function.  If it isn't, return -EINVAL.  If
-	you cannot actually change the frequency, do not define irq_set_freq.
+    *	RTC_IRQP_SET, RTC_IRQP_READ: These are emulated by the generic code.
 
-    *	RTC_PIE_ON, RTC_PIE_OFF: the irq_set_state function will be called.
+    *	RTC_PIE_ON, RTC_PIE_OFF: These are also emulated by the generic code.
 
 If all else fails, check out the rtc-test.c driver!