rtc: add support for Abracon AB-RTCMC-32.768kHz-B5ZE-S3 I2C RTC chip

This patch adds support for Abracon AB-RTCMC-32.768kHz-B5ZE-S3
RTC/Calendar module w/ I2C interface.

This support includes RTC time reading and setting, Alarm (1 minute
accuracy) reading and setting, and battery low detection.  The device also
supports frequency adjustment and two timers but those features are
currently not implemented in this driver.  Due to alarm accuracy
limitation (and current lack of timer support in the driver), UIE mode is
not supported.
Signed-off-by: Arnaud Ebalard <arno@natisbad.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Alessandro Zummo <a.zummo@towertech.it>
Cc: Peter Huewe <peter.huewe@infineon.com>
Cc: Linus Walleij <linus.walleij@linaro.org>
Cc: Thierry Reding <treding@nvidia.com>
Cc: Mark Brown <broonie@kernel.org>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Rob Herring <robherring2@gmail.com>
Cc: Pawel Moll <pawel.moll@arm.com>
Cc: Stephen Warren <swarren@wwwdotorg.org>
Cc: Ian Campbell <ijc+devicetree@hellion.org.uk>
Cc: Grant Likely <grant.likely@linaro.org>
Cc: Rob Landley <rob@landley.net>
Cc: Jason Cooper <jason@lakedaemon.net>
Cc: Guenter Roeck <linux@roeck-us.net>
Cc: Jason Gunthorpe <jgunthorpe@obsidianresearch.com>
Cc: Kumar Gala <galak@codeaurora.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

Documentation/devicetree/bindings/i2c/trivial-devices.txt

@@ -9,6 +9,7 @@ document for it just like any other devices.
 
 Compatible		Vendor / Chip
 ==========		=============
+abracon,abb5zes3		AB-RTCMC-32.768kHz-B5ZE-S3: Real Time Clock/Calendar Module with I2C Interface
 ad,ad7414		SMBus/I2C Digital Temperature Sensor in 6-Pin SOT with SMBus Alert and Over Temperature Pin
 ad,adm9240		ADM9240:  Complete System Hardware Monitor for uProcessor-Based Systems
 adi,adt7461		+/-1C TDM Extended Temp Range I.C

drivers/rtc/Kconfig

@@ -153,6 +153,17 @@ config RTC_DRV_88PM80X
 	  This driver can also be built as a module. If so, the module
 	  will be called rtc-88pm80x.
 
+config RTC_DRV_ABB5ZES3
+       depends on I2C
+       select REGMAP_I2C
+       tristate "Abracon AB-RTCMC-32.768kHz-B5ZE-S3"
+       help
+	  If you say yes here you get support for the Abracon
+	  AB-RTCMC-32.768kHz-B5ZE-S3 I2C RTC chip.
+
+	  This driver can also be built as a module. If so, the module
+	  will be called rtc-ab-b5ze-s3.
+
 config RTC_DRV_AS3722
 	tristate "ams AS3722 RTC driver"
 	depends on MFD_AS3722

drivers/rtc/Makefile

@@ -24,6 +24,7 @@ obj-$(CONFIG_RTC_DRV_88PM860X)  += rtc-88pm860x.o
 obj-$(CONFIG_RTC_DRV_88PM80X)	+= rtc-88pm80x.o
 obj-$(CONFIG_RTC_DRV_AB3100)	+= rtc-ab3100.o
 obj-$(CONFIG_RTC_DRV_AB8500)	+= rtc-ab8500.o
+obj-$(CONFIG_RTC_DRV_ABB5ZES3)	+= rtc-ab-b5ze-s3.o
 obj-$(CONFIG_RTC_DRV_AS3722)	+= rtc-as3722.o
 obj-$(CONFIG_RTC_DRV_AT32AP700X)+= rtc-at32ap700x.o
 obj-$(CONFIG_RTC_DRV_AT91RM9200)+= rtc-at91rm9200.o