rtc-m41t93.c 5.42 KB
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/*
 *
 * 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);
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	int tmp;
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	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;
	}

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	tmp = spi_w8r8(spi, M41T93_REG_FLAGS);
	if (tmp < 0)
		return tmp;

	if (tmp & M41T93_FLAG_OF) {
		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) {
			/* OF cannot be immediately reset: oscillator has to be
			 * restarted. */
			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);
		}
	}

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	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.
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	   2. oscillator fail bit (OF) is set: time is invalid.
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	*/
	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;
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		dev_warn(&spi->dev, "OF bit is set, write time to restart.\n");
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	}

	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);

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	return ret;
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}


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;

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static int m41t93_probe(struct spi_device *spi)
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{
	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;
	}

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	rtc = devm_rtc_device_register(&spi->dev, m41t93_driver.driver.name,
					&m41t93_rtc_ops, THIS_MODULE);
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	if (IS_ERR(rtc))
		return PTR_ERR(rtc);

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	spi_set_drvdata(spi, rtc);
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	return 0;
}

static struct spi_driver m41t93_driver = {
	.driver = {
		.name	= "rtc-m41t93",
	},
	.probe	= m41t93_probe,
};

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module_spi_driver(m41t93_driver);
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MODULE_AUTHOR("Nikolaus Voss <n.voss@weinmann.de>");
MODULE_DESCRIPTION("Driver for ST M41T93 SPI RTC");
MODULE_LICENSE("GPL");
MODULE_ALIAS("spi:rtc-m41t93");