rtc: add support for Maxim max6916

Add support for Maxim max6916 RTC.
Signed-off-by: Venkat Prashanth B U <venkat.prashanth2498@gmail.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>

drivers/rtc/Kconfig

@@ -670,6 +670,18 @@ config RTC_DRV_DS1390
 	  This driver can also be built as a module. If so, the module
 	  will be called rtc-ds1390.
 
+config RTC_DRV_MAX6916
+	tristate "Maxim MAX6916"
+	help
+	  If you say yes here you will get support for the
+	  Maxim MAX6916 SPI RTC chip.
+
+	  This driver only supports the RTC feature, and not other chip
+	  features such as alarms.
+
+	  This driver can also be built as a module. If so, the module
+	  will be called rtc-max6916.
+
 config RTC_DRV_R9701
 	tristate "Epson RTC-9701JE"
 	help

drivers/rtc/Makefile

@@ -85,6 +85,7 @@ obj-$(CONFIG_RTC_DRV_M48T59)	+= rtc-m48t59.o
 obj-$(CONFIG_RTC_DRV_M48T86)	+= rtc-m48t86.o
 obj-$(CONFIG_RTC_DRV_MAX6900)	+= rtc-max6900.o
 obj-$(CONFIG_RTC_DRV_MAX6902)	+= rtc-max6902.o
+obj-$(CONFIG_RTC_DRV_MAX6916)	+= rtc-max6916.o
 obj-$(CONFIG_RTC_DRV_MAX77686)	+= rtc-max77686.o
 obj-$(CONFIG_RTC_DRV_MAX8907)	+= rtc-max8907.o
 obj-$(CONFIG_RTC_DRV_MAX8925)	+= rtc-max8925.o

drivers/rtc/rtc-max6916.c

+/* rtc-max6916.c
+ *
+ * Driver for MAXIM  max6916 Low Current, SPI Compatible
+ * Real Time Clock
+ *
+ * Author : Venkat Prashanth B U <venkat.prashanth2498@gmail.com>
+ *
+ * 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/init.h>
+#include <linux/module.h>
+#include <linux/device.h>
+#include <linux/platform_device.h>
+#include <linux/rtc.h>
+#include <linux/spi/spi.h>
+#include <linux/bcd.h>
+
+/* Registers in max6916 rtc */
+
+#define MAX6916_SECONDS_REG	0x01
+#define MAX6916_MINUTES_REG	0x02
+#define MAX6916_HOURS_REG	0x03
+#define MAX6916_DATE_REG	0x04
+#define MAX6916_MONTH_REG	0x05
+#define MAX6916_DAY_REG	0x06
+#define MAX6916_YEAR_REG	0x07
+#define MAX6916_CONTROL_REG	0x08
+#define MAX6916_STATUS_REG	0x0C
+#define MAX6916_CLOCK_BURST	0x3F
+
+static int max6916_read_reg(struct device *dev, unsigned char address,
+			    unsigned char *data)
+{
+	struct spi_device *spi = to_spi_device(dev);
+
+	*data = address | 0x80;
+
+	return spi_write_then_read(spi, data, 1, data, 1);
+}
+
+static int max6916_write_reg(struct device *dev, unsigned char address,
+			     unsigned char data)
+{
+	struct spi_device *spi = to_spi_device(dev);
+	unsigned char buf[2];
+
+	buf[0] = address & 0x7F;
+	buf[1] = data;
+
+	return spi_write_then_read(spi, buf, 2, NULL, 0);
+}
+
+static int max6916_read_time(struct device *dev, struct rtc_time *dt)
+{
+	struct spi_device *spi = to_spi_device(dev);
+	int err;
+	unsigned char buf[8];
+
+	buf[0] = MAX6916_CLOCK_BURST | 0x80;
+
+	err = spi_write_then_read(spi, buf, 1, buf, 8);
+
+	if (err)
+		return err;
+
+	dt->tm_sec = bcd2bin(buf[0]);
+	dt->tm_min = bcd2bin(buf[1]);
+	dt->tm_hour = bcd2bin(buf[2] & 0x3F);
+	dt->tm_mday = bcd2bin(buf[3]);
+	dt->tm_mon = bcd2bin(buf[4]) - 1;
+	dt->tm_wday = bcd2bin(buf[5]) - 1;
+	dt->tm_year = bcd2bin(buf[6]) + 100;
+
+	return rtc_valid_tm(dt);
+}
+
+static int max6916_set_time(struct device *dev, struct rtc_time *dt)
+{
+	struct spi_device *spi = to_spi_device(dev);
+	unsigned char buf[9];
+
+	if (dt->tm_year < 100 || dt->tm_year > 199) {
+		dev_err(&spi->dev, "Year must be between 2000 and 2099. It's %d.\n",
+			dt->tm_year + 1900);
+	return -EINVAL;
+	}
+
+	buf[0] = MAX6916_CLOCK_BURST & 0x7F;
+	buf[1] = bin2bcd(dt->tm_sec);
+	buf[2] = bin2bcd(dt->tm_min);
+	buf[3] = (bin2bcd(dt->tm_hour) & 0X3F);
+	buf[4] = bin2bcd(dt->tm_mday);
+	buf[5] = bin2bcd(dt->tm_mon + 1);
+	buf[6] = bin2bcd(dt->tm_wday + 1);
+	buf[7] = bin2bcd(dt->tm_year % 100);
+	buf[8] = bin2bcd(0x00);
+
+	/* write the rtc settings */
+	return spi_write_then_read(spi, buf, 9, NULL, 0);
+}
+
+static const struct rtc_class_ops max6916_rtc_ops = {
+	.read_time = max6916_read_time,
+	.set_time = max6916_set_time,
+};
+
+static int max6916_probe(struct spi_device *spi)
+{
+	struct rtc_device *rtc;
+	unsigned char data;
+	int res;
+
+	/* spi setup with max6916 in mode 3 and bits per word as 8 */
+	spi->mode = SPI_MODE_3;
+	spi->bits_per_word = 8;
+	spi_setup(spi);
+
+	/* RTC Settings */
+	res = max6916_read_reg(&spi->dev, MAX6916_SECONDS_REG, &data);
+	if (res)
+		return res;
+
+	/* Disable the write protect of rtc */
+	max6916_read_reg(&spi->dev, MAX6916_CONTROL_REG, &data);
+	data = data & ~(1 << 7);
+	max6916_write_reg(&spi->dev, MAX6916_CONTROL_REG, data);
+
+	/*Enable oscillator,disable oscillator stop flag, glitch filter*/
+	max6916_read_reg(&spi->dev, MAX6916_STATUS_REG, &data);
+	data = data & 0x1B;
+	max6916_write_reg(&spi->dev, MAX6916_STATUS_REG, data);
+
+	/* display the settings */
+	max6916_read_reg(&spi->dev, MAX6916_CONTROL_REG, &data);
+	dev_info(&spi->dev, "MAX6916 RTC CTRL Reg = 0x%02x\n", data);
+
+	max6916_read_reg(&spi->dev, MAX6916_STATUS_REG, &data);
+	dev_info(&spi->dev, "MAX6916 RTC Status Reg = 0x%02x\n", data);
+
+	rtc = devm_rtc_device_register(&spi->dev, "max6916",
+				       &max6916_rtc_ops, THIS_MODULE);
+	if (IS_ERR(rtc))
+		return PTR_ERR(rtc);
+
+	spi_set_drvdata(spi, rtc);
+
+	return 0;
+}
+
+static struct spi_driver max6916_driver = {
+	.driver = {
+		.name = "max6916",
+	},
+	.probe = max6916_probe,
+};
+module_spi_driver(max6916_driver);
+
+MODULE_DESCRIPTION("MAX6916 SPI RTC DRIVER");
+MODULE_AUTHOR("Venkat Prashanth B U <venkat.prashanth2498@gmail.com>");
+MODULE_LICENSE("GPL v2");