rtc: ds1305/ds1306 driver

Support the Dallas/Maxim DS1305 and DS1306 RTC chips.  These use SPI, and
support alarms, NVRAM, and a trickle charger for use when their backup
power supply is a supercap or rechargeable cell.

This basic driver doesn't yet support suspend/resume or wakealarms.
Signed-off-by: NDavid Brownell <dbrownell@users.sourceforge.net>
Cc: Alessandro Zummo <a.zummo@towertech.it>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

drivers/rtc/Kconfig

@@ -282,6 +282,16 @@ config RTC_DRV_M41T94
 	  This driver can also be built as a module. If so, the module
 	  will be called rtc-m41t94.
 
+config RTC_DRV_DS1305
+	tristate "Dallas/Maxim DS1305/DS1306"
+	help
+	  Select this driver to get support for the Dallas/Maxim DS1305
+	  and DS1306 real time clock chips.  These support a trickle
+	  charger, alarms, and NVRAM in addition to the clock.
+
+	  This driver can also be built as a module. If so, the module
+	  will be called rtc-ds1305.
+
 config RTC_DRV_MAX6902
 	tristate "Maxim MAX6902"
 	help

drivers/rtc/Makefile

@@ -24,6 +24,7 @@ obj-$(CONFIG_RTC_DRV_BFIN)	+= rtc-bfin.o
 obj-$(CONFIG_RTC_DRV_CMOS)	+= rtc-cmos.o
 obj-$(CONFIG_RTC_DRV_DS1216)	+= rtc-ds1216.o
 obj-$(CONFIG_RTC_DRV_DS1302)	+= rtc-ds1302.o
+obj-$(CONFIG_RTC_DRV_DS1305)	+= rtc-ds1305.o
 obj-$(CONFIG_RTC_DRV_DS1307)	+= rtc-ds1307.o
 obj-$(CONFIG_RTC_DRV_DS1374)	+= rtc-ds1374.o
 obj-$(CONFIG_RTC_DRV_DS1511)	+= rtc-ds1511.o

include/linux/spi/ds1305.h

+#ifndef __LINUX_SPI_DS1305_H
+#define __LINUX_SPI_DS1305_H
+
+/*
+ * One-time configuration for ds1305 and ds1306 RTC chips.
+ *
+ * Put a pointer to this in spi_board_info.platform_data if you want to
+ * be sure that Linux (re)initializes this as needed ... after losing
+ * backup power, and potentially on the first boot.
+ */
+struct ds1305_platform_data {
+
+	/* Trickle charge configuration:  it's OK to leave out the MAGIC
+	 * bitmask; mask in either DS1 or DS2, and then one of 2K/4k/8K.
+	 */
+#define DS1305_TRICKLE_MAGIC	0xa0
+#define DS1305_TRICKLE_DS2	0x08	/* two diodes */
+#define DS1305_TRICKLE_DS1	0x04	/* one diode */
+#define DS1305_TRICKLE_2K	0x01	/* 2 KOhm resistance */
+#define DS1305_TRICKLE_4K	0x02	/* 4 KOhm resistance */
+#define DS1305_TRICKLE_8K	0x03	/* 8 KOhm resistance */
+	u8	trickle;
+
+	/* set only on ds1306 parts */
+	bool	is_ds1306;
+
+	/* ds1306 only:  enable 1 Hz output */
+	bool	en_1hz;
+
+	/* REVISIT:  the driver currently expects nINT0 to be wired
+	 * as the alarm IRQ.  ALM1 may also need to be set up ...
+	 */
+};
+
+#endif /* __LINUX_SPI_DS1305_H */