rtc: add basic support for ST M41T93 SPI RTC

Add basic support for ST m41t93 SPI RTCs.  Tested with factory-new and
with "run-in" species with and without backup batteries.

Signed-off-by: Nikolaus Voss <n.voss@weinmann.de>
Cc: Alessandro Zummo <a.zummo@towertech.it>
Cc: Grant Likely <grant.likely@secretlab.ca>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

3 files changed, 235 insertions, 0 deletions

diff --git a/drivers/rtc/Kconfig b/drivers/rtc/Kconfig
index 4956e416b31..0a69ed9fb45 100644
--- a/drivers/rtc/Kconfig
+++ b/drivers/rtc/Kconfig
@@ -385,6 +385,15 @@ comment "SPI RTC drivers"
 
 if SPI_MASTER
 
+config RTC_DRV_M41T93
+        tristate "ST M41T93"
+        help
+          If you say yes here you will get support for the
+          ST M41T93 SPI RTC chip.
+
+          This driver can also be built as a module. If so, the module
+          will be called rtc-m41t93.
+
 config RTC_DRV_M41T94
         tristate "ST M41T94"
         help
diff --git a/drivers/rtc/Makefile b/drivers/rtc/Makefile
index 692a79f6da3..8a9b2490c9e 100644
--- a/drivers/rtc/Makefile
+++ b/drivers/rtc/Makefile
@@ -54,6 +54,7 @@ obj-$(CONFIG_RTC_DRV_ISL12022)	+= rtc-isl12022.o
 obj-$(CONFIG_RTC_DRV_JZ4740)    += rtc-jz4740.o
 obj-$(CONFIG_RTC_DRV_LPC32XX)   += rtc-lpc32xx.o
 obj-$(CONFIG_RTC_DRV_M41T80)    += rtc-m41t80.o
+obj-$(CONFIG_RTC_DRV_M41T93)    += rtc-m41t93.o
 obj-$(CONFIG_RTC_DRV_M41T94)    += rtc-m41t94.o
 obj-$(CONFIG_RTC_DRV_M48T35)    += rtc-m48t35.o
 obj-$(CONFIG_RTC_DRV_M48T59)    += rtc-m48t59.o
diff --git a/drivers/rtc/rtc-m41t93.c b/drivers/rtc/rtc-m41t93.c
new file mode 100644
index 00000000000..1a84b3e227d
--- /dev/null
+++ b/drivers/rtc/rtc-m41t93.c
@@ -0,0 +1,225 @@
+/*
+ *
+ * Driver for ST M41T93 SPI RTC
+ *
+ * (c) 2010 Nikolaus Voss, Weinmann Medical GmbH
+ *
+ * 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/bcd.h>
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/platform_device.h>
+#include <linux/rtc.h>
+#include <linux/spi/spi.h>
+
+#define M41T93_REG_SSEC                 0
+#define M41T93_REG_ST_SEC               1
+#define M41T93_REG_MIN                  2
+#define M41T93_REG_CENT_HOUR            3
+#define M41T93_REG_WDAY                 4
+#define M41T93_REG_DAY                  5
+#define M41T93_REG_MON                  6
+#define M41T93_REG_YEAR                 7
+
+
+#define M41T93_REG_ALM_HOUR_HT          0xc
+#define M41T93_REG_FLAGS                0xf
+
+#define M41T93_FLAG_ST                  (1 << 7)
+#define M41T93_FLAG_OF                  (1 << 2)
+#define M41T93_FLAG_BL                  (1 << 4)
+#define M41T93_FLAG_HT                  (1 << 6)
+
+static inline int m41t93_set_reg(struct spi_device *spi, u8 addr, u8 data)
+{
+        u8 buf[2];
+
+        /* MSB must be '1' to write */
+        buf[0] = addr | 0x80;
+        buf[1] = data;
+
+        return spi_write(spi, buf, sizeof(buf));
+}
+
+static int m41t93_set_time(struct device *dev, struct rtc_time *tm)
+{
+        struct spi_device *spi = to_spi_device(dev);
+        u8 buf[9] = {0x80};        /* write cmd + 8 data bytes */
+        u8 * const data = &buf[1]; /* ptr to first data byte */
+
+        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);
+
+        if (tm->tm_year < 100) {
+                dev_warn(&spi->dev, "unsupported date (before 2000-01-01).\n");
+                return -EINVAL;
+        }
+
+        data[M41T93_REG_SSEC]           = 0;
+        data[M41T93_REG_ST_SEC]         = bin2bcd(tm->tm_sec);
+        data[M41T93_REG_MIN]            = bin2bcd(tm->tm_min);
+        data[M41T93_REG_CENT_HOUR]      = bin2bcd(tm->tm_hour) |
+                                                ((tm->tm_year/100-1) << 6);
+        data[M41T93_REG_DAY]            = bin2bcd(tm->tm_mday);
+        data[M41T93_REG_WDAY]           = bin2bcd(tm->tm_wday + 1);
+        data[M41T93_REG_MON]            = bin2bcd(tm->tm_mon + 1);
+        data[M41T93_REG_YEAR]           = bin2bcd(tm->tm_year % 100);
+
+        return spi_write(spi, buf, sizeof(buf));
+}
+
+
+static int m41t93_get_time(struct device *dev, struct rtc_time *tm)
+{
+        struct spi_device *spi = to_spi_device(dev);
+        const u8 start_addr = 0;
+        u8 buf[8];
+        int century_after_1900;
+        int tmp;
+        int ret = 0;
+
+        /* Check status of clock. Two states must be considered:
+           1. halt bit (HT) is set: the clock is running but update of readout
+              registers has been disabled due to power failure. This is normal
+              case after poweron. Time is valid after resetting HT bit.
+           2. oscillator fail bit (OF) is set. Oscillator has be stopped and
+              time is invalid:
+              a) OF can be immeditely reset.
+              b) OF cannot be immediately reset: oscillator has to be restarted.
+        */
+        tmp = spi_w8r8(spi, M41T93_REG_ALM_HOUR_HT);
+        if (tmp < 0)
+                return tmp;
+
+        if (tmp & M41T93_FLAG_HT) {
+                dev_dbg(&spi->dev, "HT bit is set, reenable clock update.\n");
+                m41t93_set_reg(spi, M41T93_REG_ALM_HOUR_HT,
+                               tmp & ~M41T93_FLAG_HT);
+        }
+
+        tmp = spi_w8r8(spi, M41T93_REG_FLAGS);
+        if (tmp < 0)
+                return tmp;
+
+        if (tmp & M41T93_FLAG_OF) {
+                ret = -EINVAL;
+                dev_warn(&spi->dev, "OF bit is set, resetting.\n");
+                m41t93_set_reg(spi, M41T93_REG_FLAGS, tmp & ~M41T93_FLAG_OF);
+
+                tmp = spi_w8r8(spi, M41T93_REG_FLAGS);
+                if (tmp < 0)
+                        return tmp;
+                else if (tmp & M41T93_FLAG_OF) {
+                        u8 reset_osc = buf[M41T93_REG_ST_SEC] | M41T93_FLAG_ST;
+
+                        dev_warn(&spi->dev,
+                                 "OF bit is still set, kickstarting clock.\n");
+                        m41t93_set_reg(spi, M41T93_REG_ST_SEC, reset_osc);
+                        reset_osc &= ~M41T93_FLAG_ST;
+                        m41t93_set_reg(spi, M41T93_REG_ST_SEC, reset_osc);
+                }
+        }
+
+        if (tmp & M41T93_FLAG_BL)
+                dev_warn(&spi->dev, "BL bit is set, replace battery.\n");
+
+        /* read actual time/date */
+        tmp = spi_write_then_read(spi, &start_addr, 1, buf, sizeof(buf));
+        if (tmp < 0)
+                return tmp;
+
+        tm->tm_sec      = bcd2bin(buf[M41T93_REG_ST_SEC]);
+        tm->tm_min      = bcd2bin(buf[M41T93_REG_MIN]);
+        tm->tm_hour     = bcd2bin(buf[M41T93_REG_CENT_HOUR] & 0x3f);
+        tm->tm_mday     = bcd2bin(buf[M41T93_REG_DAY]);
+        tm->tm_mon      = bcd2bin(buf[M41T93_REG_MON]) - 1;
+        tm->tm_wday     = bcd2bin(buf[M41T93_REG_WDAY] & 0x0f) - 1;
+
+        century_after_1900 = (buf[M41T93_REG_CENT_HOUR] >> 6) + 1;
+        tm->tm_year = bcd2bin(buf[M41T93_REG_YEAR]) + century_after_1900 * 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);
+
+        return ret < 0 ? ret : rtc_valid_tm(tm);
+}
+
+
+static const struct rtc_class_ops m41t93_rtc_ops = {
+        .read_time      = m41t93_get_time,
+        .set_time       = m41t93_set_time,
+};
+
+static struct spi_driver m41t93_driver;
+
+static int __devinit m41t93_probe(struct spi_device *spi)
+{
+        struct rtc_device *rtc;
+        int res;
+
+        spi->bits_per_word = 8;
+        spi_setup(spi);
+
+        res = spi_w8r8(spi, M41T93_REG_WDAY);
+        if (res < 0 || (res & 0xf8) != 0) {
+                dev_err(&spi->dev, "not found 0x%x.\n", res);
+                return -ENODEV;
+        }
+
+        rtc = rtc_device_register(m41t93_driver.driver.name,
+                &spi->dev, &m41t93_rtc_ops, THIS_MODULE);
+        if (IS_ERR(rtc))
+                return PTR_ERR(rtc);
+
+        dev_set_drvdata(&spi->dev, rtc);
+
+        return 0;
+}
+
+
+static int __devexit m41t93_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 m41t93_driver = {
+        .driver = {
+                .name   = "rtc-m41t93",
+                .bus    = &spi_bus_type,
+                .owner  = THIS_MODULE,
+        },
+        .probe  = m41t93_probe,
+        .remove = __devexit_p(m41t93_remove),
+};
+
+static __init int m41t93_init(void)
+{
+        return spi_register_driver(&m41t93_driver);
+}
+module_init(m41t93_init);
+
+static __exit void m41t93_exit(void)
+{
+        spi_unregister_driver(&m41t93_driver);
+}
+module_exit(m41t93_exit);
+
+MODULE_AUTHOR("Nikolaus Voss <n.voss@weinmann.de>");
+MODULE_DESCRIPTION("Driver for ST M41T93 SPI RTC");
+MODULE_LICENSE("GPL");
+MODULE_ALIAS("spi:rtc-m41t93");