rtc: add support for EPSON TOYOCOM RTC-7301SF/DG

This adds support for EPSON TOYOCOM RTC-7301SF/DG which has parallel
interface compatible with SRAM.

This driver supports basic clock, calendar and alarm functionality.

Tested with Microblaze linux running on Artix7 FPGA board with my own
custom IP for RTC-7301.
Signed-off-by: Akinobu Mita <akinobu.mita@gmail.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>

Documentation/devicetree/bindings/rtc/epson,rtc7301.txt

+EPSON TOYOCOM RTC-7301SF/DG
+
+Required properties:
+
+- compatible: Should be "epson,rtc7301sf" or "epson,rtc7301dg"
+- reg: Specifies base physical address and size of the registers.
+- interrupts: A single interrupt specifier.
+
+Example:
+
+rtc: rtc@44a00000 {
+	compatible = "epson,rtc7301dg";
+	reg = <0x44a00000 0x10000>;
+	interrupt-parent = <&axi_intc_0>;
+	interrupts = <3 2>;
+};

drivers/rtc/Kconfig

@@ -1705,6 +1705,17 @@ config RTC_DRV_PIC32
 	   This driver can also be built as a module. If so, the module
 	   will be called rtc-pic32
 
+config RTC_DRV_R7301
+	tristate "EPSON TOYOCOM RTC-7301SF/DG"
+	select REGMAP_MMIO
+	depends on OF && HAS_IOMEM
+	help
+	   If you say yes here you get support for the EPSON TOYOCOM
+	   RTC-7301SF/DG chips.
+
+	   This driver can also be built as a module. If so, the module
+	   will be called rtc-r7301.
+
 comment "HID Sensor RTC drivers"
 
 config RTC_DRV_HID_SENSOR_TIME

drivers/rtc/Makefile

@@ -120,6 +120,7 @@ obj-$(CONFIG_RTC_DRV_PM8XXX)	+= rtc-pm8xxx.o
 obj-$(CONFIG_RTC_DRV_PS3)	+= rtc-ps3.o
 obj-$(CONFIG_RTC_DRV_PUV3)	+= rtc-puv3.o
 obj-$(CONFIG_RTC_DRV_PXA)	+= rtc-pxa.o
+obj-$(CONFIG_RTC_DRV_R7301)	+= rtc-r7301.o
 obj-$(CONFIG_RTC_DRV_R9701)	+= rtc-r9701.o
 obj-$(CONFIG_RTC_DRV_RC5T583)	+= rtc-rc5t583.o
 obj-$(CONFIG_RTC_DRV_RK808)	+= rtc-rk808.o