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    Subject[PATCH] add support for ST M41T94 SPI RTC (patch rev. 2)
    This patch adds kernel driver for M41T94 RTC chip connected via SPI.
    I've tested it on two different AT91-based hardwares.

    This is second revision of the patch: support for century bit added,
    some comments made by Alessandro Zummo fixed.

    Signed-off-by: Kim B. Heino <Kim.Heino@bluegiga.com>


    diff -urN orig/drivers/rtc/Kconfig linux-2.6.25/drivers/rtc/Kconfig
    --- orig/drivers/rtc/Kconfig 2008-04-17 05:49:44.000000000 +0300
    +++ linux-2.6.25/drivers/rtc/Kconfig 2008-05-14 16:58:58.000000000 +0300
    @@ -266,6 +266,15 @@

    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 -urN orig/drivers/rtc/Makefile linux-2.6.25/drivers/rtc/Makefile
    --- orig/drivers/rtc/Makefile 2008-04-17 05:49:44.000000000 +0300
    +++ linux-2.6.25/drivers/rtc/Makefile 2008-05-14 16:58:58.000000000 +0300
    @@ -33,6 +33,7 @@
    obj-$(CONFIG_RTC_DRV_EP93XX) += rtc-ep93xx.o
    obj-$(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 -urN orig/drivers/rtc/rtc-m41t94.c linux-2.6.25/drivers/rtc/rtc-m41t94.c
    --- orig/drivers/rtc/rtc-m41t94.c 1970-01-01 02:00:00.000000000 +0200
    +++ linux-2.6.25/drivers/rtc/rtc-m41t94.c 2008-05-14 16:59:09.000000000 +0300
    @@ -0,0 +1,188 @@
    +/*
    + * 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
    +
    +struct m41t94 {
    + struct rtc_device *rtc;
    +};
    +
    +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;
    + struct m41t94 *m41t94;
    + int res;
    +
    + m41t94 = kzalloc(sizeof(struct m41t94), GFP_KERNEL);
    + if (!m41t94)
    + return -ENOMEM;
    + dev_set_drvdata(&spi->dev, m41t94);
    +
    + 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");
    + kfree(m41t94);
    + return res;
    + }
    +
    + rtc = rtc_device_register(m41t94_driver.driver.name,
    + &spi->dev, &m41t94_rtc_ops, THIS_MODULE);
    + if (IS_ERR(rtc)) {
    + kfree(m41t94);
    + return PTR_ERR(rtc);
    + }
    +
    + m41t94->rtc = rtc;
    +
    + return 0;
    +}
    +
    +static int __devexit m41t94_remove(struct spi_device *spi)
    +{
    + struct m41t94 *m41t94 = platform_get_drvdata(spi);
    + struct rtc_device *rtc = m41t94->rtc;
    +
    + if (rtc)
    + rtc_device_unregister(rtc);
    + kfree(m41t94);
    +
    + 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");

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