[PATCH] rtc: add support for maxim rtc max6916

[venkat.prashanth2498@gmail.com]

From: venkat-prashanth <venkat.prashanth2498@gmail.com>

This a patch to add support for
maxim rtc max6916

Signed-off-by: Venkat Prashanth B U <venkat.prashanth2498@gmail.com>
---
---
 drivers/rtc/rtc-max6916.c | 165 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 165 insertions(+)

diff --git a/drivers/rtc/rtc-max6916.c b/drivers/rtc/rtc-max6916.c
index e69de29..2085151 100644
--- a/drivers/rtc/rtc-max6916.c
+++ b/drivers/rtc/rtc-max6916.c
@@ -0,0 +1,165 @@
+/* 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	0x00
+
+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] & MAX6916_CLOCK_BURST);
+	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];
+
+	buf[0] = MAX6916_CLOCK_BURST & 0x7F;
+	buf[1] = bcd2bin(dt->tm_sec);
+	buf[2] = bcd2bin(dt->tm_min);
+	buf[3] = (bcd2bin(dt->tm_hour)&MAX6916_CLOCK_BURST);
+	buf[4] = bcd2bin(dt->tm_mday);
+	buf[5] = bcd2bin(dt->tm_mon + 1);
+	buf[6] = bcd2bin(dt->tm_wday + 1);
+
+	/* year from 1900-range of 100 in rtc from 00 to 99 */
+	dt->tm_year = dt->tm_year % 100;
+
+	buf[7] = bcd2bin(dt->tm_year);
+	buf[8] = bcd2bin(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 the oscillator,disable the oscillator stop flag,
+	and glitch filter to reduce current consumption */
+	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");
-- 
1.9.2