RTC: Add driver for DS1685 family of real time clocks

From: Joshua Kinard <[email protected]>

This adds a driver for the Dallas/Maxim DS1685-family of RTC chips. It supports the DS1685/DS1687, DS1688/DS1691, DS1689/DS1693, DS17285/DS17287, DS17485/DS17487, and DS17885/DS17887 RTC chips. These chips are commonly found in SGI O2 and SGI Octane systems. It was originally derived from a driver patch submitted by Matthias Fuchs many years ago for use in EPPC-405-UC modules, which also used these RTCs. In addition to the time-keeping functions, this RTC also handles the shutdown mechanism of the O2 and Octane and acts as a partial NVRAM for the boot PROMS in these systems.

Verified on both an SGI O2 and an SGI Octane.

---
 MAINTAINERS                |    6
 drivers/rtc/Kconfig        |   90 +
 drivers/rtc/Makefile       |    1
 drivers/rtc/rtc-ds1685.c   | 2252 +++++++++++++++++++++++++++++++++++
 include/linux/rtc/ds1685.h |  375 +++++
 5 files changed, 2724 insertions(+)

The checkpatch errors regarding "Macros with complex values should be enclosed in parenthesis" should be fine. That macro construct I copied from elsewhere in the kernel, and I don't think wrapping them in parenthesis helps at all. Please let me know of any problems, thanks!

linux-rtc-ds1685.patch

index 2fa3853..ee1cb76 100644
@@ -2937,6 +2937,12 @@ S:	Supported
 F:	drivers/input/touchscreen/cyttsp*
 F:	include/linux/input/cyttsp.h
 
+DALLAS/MAXIM DS1685-FAMILY REAL TIME CLOCK
+M:	Joshua Kinard <[email protected]>
+S:	Maintained
+F:	drivers/rtc/rtc-ds1685.c
+F:	include/linux/rtc/ds1685.h
+
 DAMA SLAVE for AX.25
 M:	Joerg Reuter <[email protected]>
 W:	http://yaina.de/jreuter/

index c8ef3e1..1b45334 100644
@@ -52,6 +52,7 @@ obj-$(CONFIG_RTC_DRV_DS1390)	+= rtc-ds1390.o
 obj-$(CONFIG_RTC_DRV_DS1511)	+= rtc-ds1511.o
 obj-$(CONFIG_RTC_DRV_DS1553)	+= rtc-ds1553.o
 obj-$(CONFIG_RTC_DRV_DS1672)	+= rtc-ds1672.o
+obj-$(CONFIG_RTC_DRV_DS1685_FAMILY)	+= rtc-ds1685.o
 obj-$(CONFIG_RTC_DRV_DS1742)	+= rtc-ds1742.o
 obj-$(CONFIG_RTC_DRV_DS2404)    += rtc-ds2404.o
 obj-$(CONFIG_RTC_DRV_DS3232)	+= rtc-ds3232.o