Add driver for the ST M41T94 SPI RTC

This RTC is used in some Calao boards. The driver code is taken from
the linux rtc-m41t94 driver

Signed-off-by: Albin Tonnerre <albin.tonnerre@free-electrons.com>

drivers/rtc/Makefile

@@ -44,6 +44,7 @@ COBJS-$(CONFIG_RTC_ISL1208) += isl1208.o
 COBJS-$(CONFIG_RTC_M41T11) += m41t11.o
 COBJS-$(CONFIG_RTC_M41T60) += m41t60.o
 COBJS-$(CONFIG_RTC_M41T62) += m41t62.o
+COBJS-$(CONFIG_RTC_M41T94) += m41t94.o
 COBJS-$(CONFIG_RTC_M48T35A) += m48t35ax.o
 COBJS-$(CONFIG_RTC_MAX6900) += max6900.o
 COBJS-$(CONFIG_RTC_MC13783) += mc13783-rtc.o

drivers/rtc/m41t94.c

@@ -0,0 +1,124 @@
+/*
+ * Driver for ST M41T94 SPI RTC
+ *
+ * Taken from the Linux kernel drivier:
+ * Copyright (C) 2008 Kim B. Heino
+ *
+ * Adaptation for U-Boot:
+ * Copyright (C) 2009
+ * Albin Tonnerre, Free Electrons <albin.tonnerre@free-electrons.com>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ */
+
+#include <common.h>
+#include <rtc.h>
+#include <spi.h>
+
+static struct spi_slave *slave;
+
+#define M41T94_REG_SECONDS	0x01
+#define M41T94_REG_MINUTES	0x02
+#define M41T94_REG_HOURS	0x03
+#define M41T94_REG_WDAY		0x04
+#define M41T94_REG_DAY		0x05
+#define M41T94_REG_MONTH	0x06
+#define M41T94_REG_YEAR		0x07
+#define M41T94_REG_HT		0x0c
+
+#define M41T94_BIT_HALT		0x40
+#define M41T94_BIT_STOP		0x80
+#define M41T94_BIT_CB		0x40
+#define M41T94_BIT_CEB		0x80
+
+int rtc_set(struct rtc_time *tm)
+{
+	u8 buf[8]; /* write cmd + 7 registers */
+	int ret;
+
+	if (!slave) {
+		slave = spi_setup_slave(CONFIG_M41T94_SPI_BUS,
+					CONFIG_M41T94_SPI_CS, 1000000,
+					SPI_MODE_3);
+		if (!slave)
+			return -1;
+	}
+	spi_claim_bus(slave);
+
+	buf[0] = 0x80 | M41T94_REG_SECONDS; /* write time + date */
+	buf[M41T94_REG_SECONDS] = bin2bcd(tm->tm_sec);
+	buf[M41T94_REG_MINUTES] = bin2bcd(tm->tm_min);
+	buf[M41T94_REG_HOURS]   = bin2bcd(tm->tm_hour);
+	buf[M41T94_REG_WDAY]    = bin2bcd(tm->tm_wday + 1);
+	buf[M41T94_REG_DAY]     = bin2bcd(tm->tm_mday);
+	buf[M41T94_REG_MONTH]   = bin2bcd(tm->tm_mon + 1);
+
+	buf[M41T94_REG_HOURS] |= M41T94_BIT_CEB;
+	if (tm->tm_year >= 100)
+		buf[M41T94_REG_HOURS] |= M41T94_BIT_CB;
+	buf[M41T94_REG_YEAR] = bin2bcd(tm->tm_year % 100);
+
+	ret = spi_xfer(slave, 64, buf, NULL, SPI_XFER_BEGIN | SPI_XFER_END);
+	spi_release_bus(slave);
+	return ret;
+}
+
+int rtc_get(struct rtc_time *tm)
+{
+	u8 buf[2];
+	int ret, hour;
+
+	if (!slave) {
+		slave = spi_setup_slave(CONFIG_M41T94_SPI_BUS,
+					CONFIG_M41T94_SPI_CS, 1000000,
+					SPI_MODE_3);
+		if (!slave)
+			return -1;
+	}
+	spi_claim_bus(slave);
+
+	/* clear halt update bit */
+	ret = spi_w8r8(slave, M41T94_REG_HT);
+	if (ret < 0)
+		return ret;
+	if (ret & M41T94_BIT_HALT) {
+		buf[0] = 0x80 | M41T94_REG_HT;
+		buf[1] = ret & ~M41T94_BIT_HALT;
+		spi_xfer(slave, 16, buf, NULL, SPI_XFER_BEGIN | SPI_XFER_END);
+	}
+
+	/* clear stop bit */
+	ret = spi_w8r8(slave, M41T94_REG_SECONDS);
+	if (ret < 0)
+		return ret;
+	if (ret & M41T94_BIT_STOP) {
+		buf[0] = 0x80 | M41T94_REG_SECONDS;
+		buf[1] = ret & ~M41T94_BIT_STOP;
+		spi_xfer(slave, 16, buf, NULL, SPI_XFER_BEGIN | SPI_XFER_END);
+	}
+
+	tm->tm_sec  = bcd2bin(spi_w8r8(slave, M41T94_REG_SECONDS));
+	tm->tm_min  = bcd2bin(spi_w8r8(slave, M41T94_REG_MINUTES));
+	hour = spi_w8r8(slave, M41T94_REG_HOURS);
+	tm->tm_hour = bcd2bin(hour & 0x3f);
+	tm->tm_wday = bcd2bin(spi_w8r8(slave, M41T94_REG_WDAY)) - 1;
+	tm->tm_mday = bcd2bin(spi_w8r8(slave, M41T94_REG_DAY));
+	tm->tm_mon  = bcd2bin(spi_w8r8(slave, M41T94_REG_MONTH)) - 1;
+	tm->tm_year = bcd2bin(spi_w8r8(slave, M41T94_REG_YEAR));
+	if ((hour & M41T94_BIT_CB) || !(hour & M41T94_BIT_CEB))
+		tm->tm_year += 100;
+
+	spi_release_bus(slave);
+	return 0;
+}
+
+void rtc_reset(void)
+{
+	/*
+	 * Could not be tested as the reset pin is not wired on
+	 * the sbc35-ag20 board
+	 */
+	return 0;
+}