text: // SPDX-License-Identifier: GPL-2.0-only
  /*
   * SPI Driver for Microchip MCP795 RTC
   *
   * Copyright (C) Josef Gajdusek <atx@atx.name>
   *
   * based on other Linux RTC drivers
   *
   * Device datasheet:
   * https://ww1.microchip.com/downloads/en/DeviceDoc/22280A.pdf
   */
  
  #include <linux/module.h>
  #include <linux/kernel.h>
  #include <linux/device.h>
  #include <linux/printk.h>
  #include <linux/spi/spi.h>
  #include <linux/rtc.h>
  #include <linux/of.h>
  #include <linux/bcd.h>
  #include <linux/delay.h>
  
  /* MCP795 Instructions, see datasheet table 3-1 */
  #define MCP795_EEREAD	0x03
  #define MCP795_EEWRITE	0x02
  #define MCP795_EEWRDI	0x04
  #define MCP795_EEWREN	0x06
  #define MCP795_SRREAD	0x05
  #define MCP795_SRWRITE	0x01
  #define MCP795_READ	0x13
  #define MCP795_WRITE	0x12
  #define MCP795_UNLOCK	0x14
  #define MCP795_IDWRITE	0x32
  #define MCP795_IDREAD	0x33
  #define MCP795_CLRWDT	0x44
  #define MCP795_CLRRAM	0x54
  
  /* MCP795 RTCC registers, see datasheet table 4-1 */
  #define MCP795_REG_SECONDS	0x01
  #define MCP795_REG_DAY		0x04
  #define MCP795_REG_MONTH	0x06
  #define MCP795_REG_CONTROL	0x08
  #define MCP795_REG_ALM0_SECONDS	0x0C
  #define MCP795_REG_ALM0_DAY	0x0F
  
  #define MCP795_ST_BIT		BIT(7)
  #define MCP795_24_BIT		BIT(6)
  #define MCP795_LP_BIT		BIT(5)
  #define MCP795_EXTOSC_BIT	BIT(3)
  #define MCP795_OSCON_BIT	BIT(5)
  #define MCP795_ALM0_BIT		BIT(4)
  #define MCP795_ALM1_BIT		BIT(5)
  #define MCP795_ALM0IF_BIT	BIT(3)
  #define MCP795_ALM0C0_BIT	BIT(4)
  #define MCP795_ALM0C1_BIT	BIT(5)
  #define MCP795_ALM0C2_BIT	BIT(6)
  
  #define SEC_PER_DAY		(24 * 60 * 60)
  
  static int mcp795_rtcc_read(struct device *dev, u8 addr, u8 *buf, u8 count)
  {
  	struct spi_device *spi = to_spi_device(dev);
  	int ret;
  	u8 tx[2];
  
  	tx[0] = MCP795_READ;
  	tx[1] = addr;
  	ret = spi_write_then_read(spi, tx, sizeof(tx), buf, count);
  
  	if (ret)
  		dev_err(dev, "Failed reading %d bytes from address %x.\n",
  					count, addr);
  
  	return ret;
  }
  
  static int mcp795_rtcc_write(struct device *dev, u8 addr, u8 *data, u8 count)
  {
  	struct spi_device *spi = to_spi_device(dev);
  	int ret;
  	u8 tx[257];
  
  	tx[0] = MCP795_WRITE;
  	tx[1] = addr;
  	memcpy(&tx[2], data, count);
  
  	ret = spi_write(spi, tx, 2 + count);
  
  	if (ret)
  		dev_err(dev, "Failed to write %d bytes to address %x.\n",
  					count, addr);
  
  	return ret;
  }
  
  static int mcp795_rtcc_set_bits(struct device *dev, u8 addr, u8 mask, u8 state)
  {
  	int ret;
  	u8 tmp;
  
  	ret = mcp795_rtcc_read(dev, addr, &tmp, 1);
  	if (ret)
  		return ret;
  
  	if ((tmp & mask) != state) {
  		tmp = (tmp & ~mask) | state;
  		ret = mcp795_rtcc_write(dev, addr, &tmp, 1);
  	}
  
  	return ret;
  }
  
  static int mcp795_stop_oscillator(struct device *dev, bool *extosc)
  {
  	int retries = 5;
  	int ret;
  	u8 data;
  
  	ret = mcp795_rtcc_set_bits(dev, MCP795_REG_SECONDS, MCP795_ST_BIT, 0);
  	if (ret)
  		return ret;
  	ret = mcp795_rtcc_read(dev, MCP795_REG_CONTROL, &data, 1);
  	if (ret)
  		return ret;
  	*extosc = !!(data & MCP795_EXTOSC_BIT);
  	ret = mcp795_rtcc_set_bits(
  				dev, MCP795_REG_CONTROL, MCP795_EXTOSC_BIT, 0);
  	if (ret)
  		return ret;
  	/* wait for the OSCON bit to clear */
  	do {
  		usleep_range(700, 800);
  		ret = mcp795_rtcc_read(dev, MCP795_REG_DAY, &data, 1);
  		if (ret)
  			break;
  		if (!(data & MCP795_OSCON_BIT))
  			break;
  
  	} while (--retries);
  
  	return !retries ? -EIO : ret;
  }
  
  static int mcp795_start_oscillator(struct device *dev, bool *extosc)
  {
  	if (extosc) {
  		u8 data = *extosc ? MCP795_EXTOSC_BIT : 0;
  		int ret;
  
  		ret = mcp795_rtcc_set_bits(
  			dev, MCP795_REG_CONTROL, MCP795_EXTOSC_BIT, data);
  		if (ret)
  			return ret;
  	}
  	return mcp795_rtcc_set_bits(
  			dev, MCP795_REG_SECONDS, MCP795_ST_BIT, MCP795_ST_BIT);
  }
  
  /* Enable or disable Alarm 0 in RTC */
  static int mcp795_update_alarm(struct device *dev, bool enable)
  {
  	int ret;
  
  	dev_dbg(dev, "%s alarm\n", enable ? "Enable" : "Disable");
  
  	if (enable) {
  		/* clear ALM0IF (Alarm 0 Interrupt Flag) bit */
  		ret = mcp795_rtcc_set_bits(dev, MCP795_REG_ALM0_DAY,
  					MCP795_ALM0IF_BIT, 0);
  		if (ret)
  			return ret;
  		/* enable alarm 0 */
  		ret = mcp795_rtcc_set_bits(dev, MCP795_REG_CONTROL,
  					MCP795_ALM0_BIT, MCP795_ALM0_BIT);
  	} else {
  		/* disable alarm 0 and alarm 1 */
  		ret = mcp795_rtcc_set_bits(dev, MCP795_REG_CONTROL,
  					MCP795_ALM0_BIT | MCP795_ALM1_BIT, 0);
  	}
  	return ret;
  }
  
  static int mcp795_set_time(struct device *dev, struct rtc_time *tim)
  {
  	int ret;
  	u8 data[7];
  	bool extosc;
  
  	/* Stop RTC and store current value of EXTOSC bit */
  	ret = mcp795_stop_oscillator(dev, &extosc);
  	if (ret)
  		return ret;
  
  	/* Read first, so we can leave config bits untouched */
  	ret = mcp795_rtcc_read(dev, MCP795_REG_SECONDS, data, sizeof(data));
  
  	if (ret)
  		return ret;
  
  	data[0] = (data[0] & 0x80) | bin2bcd(tim->tm_sec);
  	data[1] = (data[1] & 0x80) | bin2bcd(tim->tm_min);
  	data[2] = bin2bcd(tim->tm_hour);
  	data[3] = (data[3] & 0xF8) | bin2bcd(tim->tm_wday + 1);
  	data[4] = bin2bcd(tim->tm_mday);
  	data[5] = (data[5] & MCP795_LP_BIT) | bin2bcd(tim->tm_mon + 1);
  
  	if (tim->tm_year > 100)
  		tim->tm_year -= 100;
  
  	data[6] = bin2bcd(tim->tm_year);
  
  	/* Always write the date and month using a separate Write command.
  	 * This is a workaround for a know silicon issue that some combinations
  	 * of date and month values may result in the date being reset to 1.
  	 */
  	ret = mcp795_rtcc_write(dev, MCP795_REG_SECONDS, data, 5);
  	if (ret)
  		return ret;
  
  	ret = mcp795_rtcc_write(dev, MCP795_REG_MONTH, &data[5], 2);
  	if (ret)
  		return ret;
  
  	/* Start back RTC and restore previous value of EXTOSC bit.
  	 * There is no need to clear EXTOSC bit when the previous value was 0
  	 * because it was already cleared when stopping the RTC oscillator.
  	 */
  	ret = mcp795_start_oscillator(dev, extosc ? &extosc : NULL);
  	if (ret)
  		return ret;
  
  	dev_dbg(dev, "Set mcp795: %ptR\n", tim);
  
  	return 0;
  }
  
  static int mcp795_read_time(struct device *dev, struct rtc_time *tim)
  {
  	int ret;
  	u8 data[7];
  
  	ret = mcp795_rtcc_read(dev, MCP795_REG_SECONDS, data, sizeof(data));
  
  	if (ret)
  		return ret;
  
  	tim->tm_sec	= bcd2bin(data[0] & 0x7F);
  	tim->tm_min	= bcd2bin(data[1] & 0x7F);
  	tim->tm_hour	= bcd2bin(data[2] & 0x3F);
  	tim->tm_wday	= bcd2bin(data[3] & 0x07) - 1;
  	tim->tm_mday	= bcd2bin(data[4] & 0x3F);
  	tim->tm_mon	= bcd2bin(data[5] & 0x1F) - 1;
  	tim->tm_year	= bcd2bin(data[6]) + 100; /* Assume we are in 20xx */
  
  	dev_dbg(dev, "Read from mcp795: %ptR\n", tim);
  
  	return 0;
  }
  
  static int mcp795_set_alarm(struct device *dev, struct rtc_wkalrm *alm)
  {
  	struct rtc_time now_tm;
  	time64_t now;
  	time64_t later;
  	u8 tmp[6];
  	int ret;
  
  	/* Read current time from RTC hardware */
  	ret = mcp795_read_time(dev, &now_tm);
  	if (ret)
  		return ret;
  	/* Get the number of seconds since 1970 */
  	now = rtc_tm_to_time64(&now_tm);
  	later = rtc_tm_to_time64(&alm->time);
  	if (later <= now)
  		return -EINVAL;
  	/* make sure alarm fires within the next one year */
  	if ((later - now) >=
  		(SEC_PER_DAY * (365 + is_leap_year(alm->time.tm_year))))
  		return -EDOM;
  	/* disable alarm */
  	ret = mcp795_update_alarm(dev, false);
  	if (ret)
  		return ret;
  	/* Read registers, so we can leave configuration bits untouched */
  	ret = mcp795_rtcc_read(dev, MCP795_REG_ALM0_SECONDS, tmp, sizeof(tmp));
  	if (ret)
  		return ret;
  
  	alm->time.tm_year	= -1;
  	alm->time.tm_isdst	= -1;
  	alm->time.tm_yday	= -1;
  
  	tmp[0] = (tmp[0] & 0x80) | bin2bcd(alm->time.tm_sec);
  	tmp[1] = (tmp[1] & 0x80) | bin2bcd(alm->time.tm_min);
  	tmp[2] = (tmp[2] & 0xE0) | bin2bcd(alm->time.tm_hour);
  	tmp[3] = (tmp[3] & 0x80) | bin2bcd(alm->time.tm_wday + 1);
  	/* set alarm match: seconds, minutes, hour, day, date and month */
  	tmp[3] |= (MCP795_ALM0C2_BIT | MCP795_ALM0C1_BIT | MCP795_ALM0C0_BIT);
  	tmp[4] = (tmp[4] & 0xC0) | bin2bcd(alm->time.tm_mday);
  	tmp[5] = (tmp[5] & 0xE0) | bin2bcd(alm->time.tm_mon + 1);
  
  	ret = mcp795_rtcc_write(dev, MCP795_REG_ALM0_SECONDS, tmp, sizeof(tmp));
  	if (ret)
  		return ret;
  
  	/* enable alarm if requested */
  	if (alm->enabled) {
  		ret = mcp795_update_alarm(dev, true);
  		if (ret)
  			return ret;
  		dev_dbg(dev, "Alarm IRQ armed\n");
  	}
  	dev_dbg(dev, "Set alarm: %ptRdr(%d) %ptRt\n",
  		&alm->time, alm->time.tm_wday, &alm->time);
  	return 0;
  }
  
  static int mcp795_read_alarm(struct device *dev, struct rtc_wkalrm *alm)
  {
  	u8 data[6];
  	int ret;
  
  	ret = mcp795_rtcc_read(
  			dev, MCP795_REG_ALM0_SECONDS, data, sizeof(data));
  	if (ret)
  		return ret;
  
  	alm->time.tm_sec	= bcd2bin(data[0] & 0x7F);
  	alm->time.tm_min	= bcd2bin(data[1] & 0x7F);
  	alm->time.tm_hour	= bcd2bin(data[2] & 0x1F);
  	alm->time.tm_wday	= bcd2bin(data[3] & 0x07) - 1;
  	alm->time.tm_mday	= bcd2bin(data[4] & 0x3F);
  	alm->time.tm_mon	= bcd2bin(data[5] & 0x1F) - 1;
  	alm->time.tm_year	= -1;
  	alm->time.tm_isdst	= -1;
  	alm->time.tm_yday	= -1;
  
  	dev_dbg(dev, "Read alarm: %ptRdr(%d) %ptRt\n",
  		&alm->time, alm->time.tm_wday, &alm->time);
  	return 0;
  }
  
  static int mcp795_alarm_irq_enable(struct device *dev, unsigned int enabled)
  {
  	return mcp795_update_alarm(dev, !!enabled);
  }
  
  static irqreturn_t mcp795_irq(int irq, void *data)
  {
  	struct spi_device *spi = data;
  	struct rtc_device *rtc = spi_get_drvdata(spi);
  	struct mutex *lock = &rtc->ops_lock;
  	int ret;
  
  	mutex_lock(lock);
  
  	/* Disable alarm.
  	 * There is no need to clear ALM0IF (Alarm 0 Interrupt Flag) bit,
  	 * because it is done every time when alarm is enabled.
  	 */
  	ret = mcp795_update_alarm(&spi->dev, false);
  	if (ret)
  		dev_err(&spi->dev,
  			"Failed to disable alarm in IRQ (ret=%d)\n", ret);
  	rtc_update_irq(rtc, 1, RTC_AF | RTC_IRQF);
  
  	mutex_unlock(lock);
  
  	return IRQ_HANDLED;
  }
  
  static const struct rtc_class_ops mcp795_rtc_ops = {
  		.read_time = mcp795_read_time,
  		.set_time = mcp795_set_time,
  		.read_alarm = mcp795_read_alarm,
  		.set_alarm = mcp795_set_alarm,
  		.alarm_irq_enable = mcp795_alarm_irq_enable
  };
  
  static int mcp795_probe(struct spi_device *spi)
  {
  	struct rtc_device *rtc;
  	int ret;
  
  	spi->mode = SPI_MODE_0;
  	spi->bits_per_word = 8;
  	ret = spi_setup(spi);
  	if (ret) {
  		dev_err(&spi->dev, "Unable to setup SPI\n");
  		return ret;
  	}
  
  	/* Start the oscillator but don't set the value of EXTOSC bit */
  	mcp795_start_oscillator(&spi->dev, NULL);
  	/* Clear the 12 hour mode flag*/
  	mcp795_rtcc_set_bits(&spi->dev, 0x03, MCP795_24_BIT, 0);
  
  	rtc = devm_rtc_device_register(&spi->dev, "rtc-mcp795",
  					&mcp795_rtc_ops, THIS_MODULE);
  	if (IS_ERR(rtc))
  		return PTR_ERR(rtc);
  
  	spi_set_drvdata(spi, rtc);
  
  	if (spi->irq > 0) {
  		dev_dbg(&spi->dev, "Alarm support enabled\n");
  
  		/* Clear any pending alarm (ALM0IF bit) before requesting
  		 * the interrupt.
  		 */
  		mcp795_rtcc_set_bits(&spi->dev, MCP795_REG_ALM0_DAY,
  					MCP795_ALM0IF_BIT, 0);
  		ret = devm_request_threaded_irq(&spi->dev, spi->irq, NULL,
  				mcp795_irq, IRQF_TRIGGER_FALLING | IRQF_ONESHOT,
  				dev_name(&rtc->dev), spi);
  		if (ret)
  			dev_err(&spi->dev, "Failed to request IRQ: %d: %d\n",
  						spi->irq, ret);
  		else
  			device_init_wakeup(&spi->dev, true);
  	}
  	return 0;
  }
  
  #ifdef CONFIG_OF
  static const struct of_device_id mcp795_of_match[] = {
  	{ .compatible = "maxim,mcp795" },
  	{ }
  };
  MODULE_DEVICE_TABLE(of, mcp795_of_match);
  #endif
  
  static struct spi_driver mcp795_driver = {
  		.driver = {
  				.name = "rtc-mcp795",
  				.of_match_table = of_match_ptr(mcp795_of_match),
  		},
  		.probe = mcp795_probe,
  };
  
  module_spi_driver(mcp795_driver);
  
  MODULE_DESCRIPTION("MCP795 RTC SPI Driver");
  MODULE_AUTHOR("Josef Gajdusek <atx@atx.name>");
  MODULE_LICENSE("GPL");
  MODULE_ALIAS("spi:mcp795");
  