rtc: avoid legacy drivers with generic framework

Kconfig tweaks to help reduce RTC configuration bugs, by avoiding
legacy RTC drivers when the generic RTC framework is enabled:

- If rtc-cmos is selected, disable the legacy rtc driver;

- When using generic RTC on x86, enable rtc-cmos by default;

- In the old "chardev RTC" section of Kconfig, add a comment
warning people off these (seven) legacy RTC drivers when
the generic framework is in use.

People can still use the legacy drivers if they want (or need) to.

This doesn't fix the broken dependencies for the legacy "CMOS" RTC driver.
Ideally it would be a full list of platforms where it works, not a partial
list of ones where it won't. Or better yet, it would depend on a
"HAVE_CMOS_RTC" flag defined by various platforms ... surely there's a
Kconfig style guideline lurking there.

Signed-off-by: David Brownell <[e-mail]>
Acked-by: Alessandro Zummo <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

drivers/char/Kconfig

···
 	  To compile this driver as a module, choose M here: the
 	  module will be called nvram.
 
+#
+# These legacy RTC drivers just cause too many conflicts with the generic
+# RTC framework ... let's not even try to coexist any more.
+#
+if RTC_LIB=n
+
 config RTC
 	tristate "Enhanced Real Time Clock Support"
-	depends on !PPC && !PARISC && !IA64 && !M68K && !SPARC && !FRV && !ARM && !SUPERH && !S390 && !AVR32
+	depends on !PPC && !PARISC && !IA64 && !M68K && !SPARC && !FRV \
+			&& !ARM && !SUPERH && !S390 && !AVR32
 	---help---
 	  If you say Y here and create a character special file /dev/rtc with
 	  major number 10 and minor number 135 using mknod ("man mknod"), you
···
 	  major number 121 and minor number 0 using mknod ("man mknod"), you
 	  will get access to the real time clock (or hardware clock) built
 	  into your computer.
+
+endif # RTC_LIB
 
 config COBALT_LCD
 	bool "Support for Cobalt LCD"

drivers/rtc/Kconfig

···
 
 if RTC_CLASS
 
-if GEN_RTC || RTC
-comment "Conflicting RTC option has been selected, check GEN_RTC and RTC"
-endif
-
 config RTC_HCTOSYS
 	bool "Set system time from RTC on startup and resume"
 	depends on RTC_CLASS = y
···
 config RTC_DRV_CMOS
 	tristate "PC-style 'CMOS'"
 	depends on X86 || ALPHA || ARM || M32R || ATARI || PPC || MIPS
+	default y if X86
 	help
 	  Say "yes" here to get direct support for the real time clock
 	  found in every PC or ACPI-based system, and some other boards.