rtc: add support for ST M41T94 SPI RTC

This patch adds kernel driver for M41T94 RTC chip connected via SPI.
I've tested it on two different AT91-based hardwares.

This is third revision of the patch: some comments made by
Alessandro Zummo fixed.

Revision two added support for century bit and fixes.

Signed-off-by: Kim B. Heino <Kim.Heino@bluegiga.com>
Signed-off-by: Alessandro Zummo <a.zummo@towertech.it>
Cc: David Brownell <david-b@pacbell.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

3 files changed, 183 insertions, 0 deletions

diff --git a/drivers/rtc/Kconfig b/drivers/rtc/Kconfig
index fc85bf2e4a97..beffb834c440 100644
--- a/drivers/rtc/Kconfig
+++ b/drivers/rtc/Kconfig
@@ -273,6 +273,15 @@ comment "SPI RTC drivers"
 
 if SPI_MASTER
 
+config RTC_DRV_M41T94
+        tristate "ST M41T94"
+        help
+          If you say yes here you will get support for the
+          ST M41T94 SPI RTC chip.
+
+          This driver can also be built as a module. If so, the module
+          will be called rtc-m41t94.
+
 config RTC_DRV_MAX6902
         tristate "Maxim MAX6902"
         help
diff --git a/drivers/rtc/Makefile b/drivers/rtc/Makefile
index b5d9d67df887..b0e1af54f800 100644
--- a/drivers/rtc/Makefile
+++ b/drivers/rtc/Makefile
@@ -34,6 +34,7 @@ obj-$(CONFIG_RTC_DRV_EP93XX)	+= rtc-ep93xx.o
 obj-$(CONFIG_RTC_DRV_FM3130)    += rtc-fm3130.o
 obj-$(CONFIG_RTC_DRV_ISL1208)   += rtc-isl1208.o
 obj-$(CONFIG_RTC_DRV_M41T80)    += rtc-m41t80.o
+obj-$(CONFIG_RTC_DRV_M41T94)    += rtc-m41t94.o
 obj-$(CONFIG_RTC_DRV_M48T59)    += rtc-m48t59.o
 obj-$(CONFIG_RTC_DRV_M48T86)    += rtc-m48t86.o
 obj-$(CONFIG_RTC_DRV_MAX6900)   += rtc-max6900.o
diff --git a/drivers/rtc/rtc-m41t94.c b/drivers/rtc/rtc-m41t94.c
new file mode 100644
index 000000000000..9b19499c829e
--- /dev/null
+++ b/drivers/rtc/rtc-m41t94.c
@@ -0,0 +1,173 @@
+/*
+ * Driver for ST M41T94 SPI RTC
+ *
+ * Copyright (C) 2008 Kim B. Heino
+ *
+ * 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 <linux/module.h>
+#include <linux/kernel.h>
+#include <linux/platform_device.h>
+#include <linux/rtc.h>
+#include <linux/spi/spi.h>
+#include <linux/bcd.h>
+
+#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
+
+static int m41t94_set_time(struct device *dev, struct rtc_time *tm)
+{
+        struct spi_device *spi = to_spi_device(dev);
+        u8 buf[8]; /* write cmd + 7 registers */
+
+        dev_dbg(dev, "%s secs=%d, mins=%d, "
+                "hours=%d, mday=%d, mon=%d, year=%d, wday=%d\n",
+                "write", tm->tm_sec, tm->tm_min,
+                tm->tm_hour, tm->tm_mday,
+                tm->tm_mon, tm->tm_year, tm->tm_wday);
+
+        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);
+
+        return spi_write(spi, buf, 8);
+}
+
+static int m41t94_read_time(struct device *dev, struct rtc_time *tm)
+{
+        struct spi_device *spi = to_spi_device(dev);
+        u8 buf[2];
+        int ret, hour;
+
+        /* clear halt update bit */
+        ret = spi_w8r8(spi, 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_write(spi, buf, 2);
+        }
+
+        /* clear stop bit */
+        ret = spi_w8r8(spi, 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_write(spi, buf, 2);
+        }
+
+        tm->tm_sec  = BCD2BIN(spi_w8r8(spi, M41T94_REG_SECONDS));
+        tm->tm_min  = BCD2BIN(spi_w8r8(spi, M41T94_REG_MINUTES));
+        hour = spi_w8r8(spi, M41T94_REG_HOURS);
+        tm->tm_hour = BCD2BIN(hour & 0x3f);
+        tm->tm_wday = BCD2BIN(spi_w8r8(spi, M41T94_REG_WDAY)) - 1;
+        tm->tm_mday = BCD2BIN(spi_w8r8(spi, M41T94_REG_DAY));
+        tm->tm_mon  = BCD2BIN(spi_w8r8(spi, M41T94_REG_MONTH)) - 1;
+        tm->tm_year = BCD2BIN(spi_w8r8(spi, M41T94_REG_YEAR));
+        if ((hour & M41T94_BIT_CB) || !(hour & M41T94_BIT_CEB))
+                tm->tm_year += 100;
+
+        dev_dbg(dev, "%s secs=%d, mins=%d, "
+                "hours=%d, mday=%d, mon=%d, year=%d, wday=%d\n",
+                "read", tm->tm_sec, tm->tm_min,
+                tm->tm_hour, tm->tm_mday,
+                tm->tm_mon, tm->tm_year, tm->tm_wday);
+
+        /* initial clock setting can be undefined */
+        return rtc_valid_tm(tm);
+}
+
+static const struct rtc_class_ops m41t94_rtc_ops = {
+        .read_time      = m41t94_read_time,
+        .set_time       = m41t94_set_time,
+};
+
+static struct spi_driver m41t94_driver;
+
+static int __devinit m41t94_probe(struct spi_device *spi)
+{
+        struct rtc_device *rtc;
+        int res;
+
+        spi->bits_per_word = 8;
+        spi_setup(spi);
+
+        res = spi_w8r8(spi, M41T94_REG_SECONDS);
+        if (res < 0) {
+                dev_err(&spi->dev, "not found.\n");
+                return res;
+        }
+
+        rtc = rtc_device_register(m41t94_driver.driver.name,
+                &spi->dev, &m41t94_rtc_ops, THIS_MODULE);
+        if (IS_ERR(rtc))
+                return PTR_ERR(rtc);
+
+        dev_set_drvdata(&spi->dev, rtc);
+
+        return 0;
+}
+
+static int __devexit m41t94_remove(struct spi_device *spi)
+{
+        struct rtc_device *rtc = platform_get_drvdata(spi);
+
+        if (rtc)
+                rtc_device_unregister(rtc);
+
+        return 0;
+}
+
+static struct spi_driver m41t94_driver = {
+        .driver = {
+                .name   = "rtc-m41t94",
+                .bus    = &spi_bus_type,
+                .owner  = THIS_MODULE,
+        },
+        .probe  = m41t94_probe,
+        .remove = __devexit_p(m41t94_remove),
+};
+
+static __init int m41t94_init(void)
+{
+        return spi_register_driver(&m41t94_driver);
+}
+
+module_init(m41t94_init);
+
+static __exit void m41t94_exit(void)
+{
+        spi_unregister_driver(&m41t94_driver);
+}
+
+module_exit(m41t94_exit);
+
+MODULE_AUTHOR("Kim B. Heino <Kim.Heino@bluegiga.com>");
+MODULE_DESCRIPTION("Driver for ST M41T94 SPI RTC");
+MODULE_LICENSE("GPL");