Re: [PATCH] Add Dallas DS1390 RTC chip

Re: [PATCH] Add Dallas DS1390 RTC chip

[Alessandro Zummo]

On Tue, 14 Oct 2008 09:05:18 +0100
Mark Jackson <mpfj@mimc.co.uk> wrote:

 Hi Mark,

   a few notes below:

> +#include <linux/module.h>
> +#include <linux/version.h>
> +
> +#include <linux/kernel.h>
> +#include <linux/platform_device.h>
> +#include <linux/init.h>
> +#include <linux/rtc.h>
> +#include <linux/spi/spi.h>
> +#include <linux/bcd.h>
> +#include <linux/delay.h>

 Please check that you require all of those includes.


> +struct ds1390
> +{
> +	struct rtc_device *rtc;
> +	u8 buf[9];	/* cmd + 8 registers */
> +	u8 tx_buf[2];
> +	u8 rx_buf[2];
> +};
> +
> +static void ds1390_set_reg(struct device *dev, unsigned char address,
> +				unsigned char data)
> +{
> +	struct spi_device *spi = to_spi_device(dev);
> +	unsigned char buf[2];
> +
> +	/* MSB must be '1' to write */
> +	buf[0] = address | 0x80;
> +	buf[1] = data;
> +
> +	spi_write(spi, buf, 2);
> +}
> +
> +static int ds1390_get_reg(struct device *dev, unsigned char address,
> +				unsigned char *data)
> +{
> +	struct spi_device *spi = to_spi_device(dev);
> +	struct ds1390 *chip = dev_get_drvdata(dev);
> +	struct spi_message message;
> +	struct spi_transfer xfer;
> +	int status;
> +
> +	if (!data)
> +		return -EINVAL;
> +
> +	/* Build our spi message */
> +	spi_message_init(&message);
> +	memset(&xfer, 0, sizeof(xfer));
> +	xfer.len = 2;
> +	/* Can tx_buf and rx_buf be equal? The doc in spi.h is not sure... */
> +	xfer.tx_buf = chip->tx_buf;
> +	xfer.rx_buf = chip->rx_buf;

 you use the same buffer a few functions below. either
 one way or the other. please investigate with the spi subsystem maintainer.


> +
> +	/* Clear MSB to indicate read */
> +	chip->tx_buf[0] = address & 0x7f;
> +
> +	spi_message_add_tail(&xfer, &message);
> +
> +	/* do the i/o */
> +	status = spi_sync(spi, &message);
> +	if (status == 0)
> +	{
> +		status = message.status;
> +	}
> +	else
> +	{
> +		return status;
> +	}

 should be cleaner in this way:

 if (status != 0)
	return status;

 *data = chip->rx_buf[1];

 return message.status;


> +static int ds1390_get_datetime(struct device *dev, struct rtc_time *dt)
> +{
> +	struct spi_device *spi = to_spi_device(dev);
> +	struct ds1390 *chip = dev_get_drvdata(dev);
> +	struct spi_message message;
> +	struct spi_transfer xfer;
> +	int status;
> +
> +	/* build the message */
> +	spi_message_init(&message);
> +	memset(&xfer, 0, sizeof(xfer));
> +	xfer.len = 1 + 7;	/* read command + 7 registers */
> +	xfer.tx_buf = chip->buf;
> +	xfer.rx_buf = chip->buf;

 the buffer mentioned above.


> +	chip->buf[0] = DS1390_REG_SECONDS;
> +	spi_message_add_tail(&xfer, &message);
> +
> +	/* do the i/o */
> +	status = spi_sync(spi, &message);
> +	if (status == 0)
> +	{
> +		status = message.status;
> +	}
> +	else
> +	{
> +		return status;
> +	}

 ditto.

> +	/* The chip sends data in this order:
> +	 * Seconds, Minutes, Hours, Day, Date, Month / Century, Year */
> +	dt->tm_sec	= BCD2BIN(chip->buf[1]);
> +	dt->tm_min	= BCD2BIN(chip->buf[2]);
> +	dt->tm_hour	= BCD2BIN(chip->buf[3]);
> +	dt->tm_wday	= BCD2BIN(chip->buf[4]);
> +	dt->tm_mday	= BCD2BIN(chip->buf[5]);
> +	/* mask off century bit */
> +	dt->tm_mon	= BCD2BIN(chip->buf[6] & 0x7f) - 1;
> +	/* adjust for century bit */
> +	dt->tm_year = BCD2BIN(chip->buf[7]) + ((chip->buf[6] & 0x80) ? 100 : 0);
> +
> +	return 0;
> +}
> +
> +static int ds1390_set_datetime(struct device *dev, struct rtc_time *dt)
> +{
> +	struct spi_device *spi = to_spi_device(dev);
> +	struct ds1390 *chip = dev_get_drvdata(dev);
> +	struct spi_message message;
> +	struct spi_transfer xfer;
> +	int status;
> +
> +	/* build the message */
> +	spi_message_init(&message);
> +	memset(&xfer, 0, sizeof(xfer));
> +	xfer.len = 1 + 8;	/* write command + 8 registers */
> +	xfer.tx_buf = chip->buf;
> +	xfer.rx_buf = chip->buf;
> +	chip->buf[0] = DS1390_REG_SECONDS | 0x80;
> +	chip->buf[1] = BIN2BCD(dt->tm_sec);
> +	chip->buf[2] = BIN2BCD(dt->tm_min);
> +	chip->buf[3] = BIN2BCD(dt->tm_hour);
> +	chip->buf[4] = BIN2BCD(dt->tm_wday);
> +	chip->buf[5] = BIN2BCD(dt->tm_mday);
> +	chip->buf[6] = BIN2BCD(dt->tm_mon + 1) | ((dt->tm_year > 99) ? 0x80 : 0x00);
> +	chip->buf[7] = BIN2BCD(dt->tm_year % 100);
> +	spi_message_add_tail(&xfer, &message);
> +
> +	/* do the i/o */
> +	status = spi_sync(spi, &message);
> +	if (status == 0)
> +	{
> +		status = message.status;
> +	}
> +	else
> +	{
> +		return status;
> +	}

 if status == 0, status is not used anymore, so you can
 just return if != 0;

> +	return 0;
> +}
> +
> +static int ds1390_read_time(struct device *dev, struct rtc_time *tm)
> +{
> +	return ds1390_get_datetime(dev, tm);
> +}
> +
> +static int ds1390_set_time(struct device *dev, struct rtc_time *tm)
> +{
> +	return ds1390_set_datetime(dev, tm);
> +}
> +
> +static const struct rtc_class_ops ds1390_rtc_ops = {
> +	.read_time	= ds1390_read_time,
> +	.set_time	= ds1390_set_time,
> +};
> +
> +static int __devinit ds1390_probe(struct spi_device *spi)
> +{
> +	struct rtc_device *rtc;
> +	unsigned char tmp;
> +	struct ds1390 *chip;
> +	int res;
> +
> +	printk("DS1390 SPI RTC driver\n");
> +
> +	rtc = rtc_device_register("ds1390",
> +				&spi->dev, &ds1390_rtc_ops, THIS_MODULE);
> +	if (IS_ERR(rtc))
> +	{
> +		printk("RTC : unable to register device\n");
> +		return PTR_ERR(rtc);
> +	}
> +
> +	spi->mode = SPI_MODE_3;
> +	spi->bits_per_word = 8;
> +	spi_setup(spi);
> +
> +	chip = kzalloc(sizeof *chip, GFP_KERNEL);
> +	if (!chip) {
> +		printk("RTC : unable to allocate device memory\n");
> +		rtc_device_unregister(rtc);
> +		return -ENOMEM;
> +	}
> +	chip->rtc = rtc;
> +	dev_set_drvdata(&spi->dev, chip);
> +
> +	res = ds1390_get_reg(&spi->dev, DS1390_REG_SECONDS, &tmp);
> +	if (res) {
> +		printk("RTC : unable to read device\n");
> +		rtc_device_unregister(rtc);
> +		return res;
> +	}
> +
> +	return 0;
> +}
> +
> +static int __devexit ds1390_remove(struct spi_device *spi)
> +{
> +	struct ds1390 *chip = platform_get_drvdata(spi);
> +	struct rtc_device *rtc = chip->rtc;
> +
> +	if (rtc)
> +		rtc_device_unregister(rtc);
> +
> +	kfree(chip);
> +
> +	return 0;
> +}
> +
> +static struct spi_driver ds1390_driver = {
> +	.driver = {
> +		.name	= "rtc-ds1390",
> +		.bus	= &spi_bus_type,
> +		.owner	= THIS_MODULE,
> +	},
> +	.probe	= ds1390_probe,
> +	.remove = __devexit_p(ds1390_remove),
> +};
> +
> +static __init int ds1390_init(void)
> +{
> +	return spi_register_driver(&ds1390_driver);
> +}
> +module_init(ds1390_init);
> +
> +static __exit void ds1390_exit(void)
> +{
> +	spi_unregister_driver(&ds1390_driver);
> +}
> +module_exit(ds1390_exit);
> +
> +MODULE_DESCRIPTION ("DS1390 SPI RTC driver");
> +MODULE_AUTHOR ("Mark Jackson");

 you email here please.

> +MODULE_LICENSE ("GPL");


-- 

 Best regards,

 Alessandro Zummo,
  Tower Technologies - Torino, Italy

  http://www.towertech.it

Re: [PATCH] Add Dallas DS1390 RTC chip

[Mark Jackson]

David ... please see comments below regarding spi buffers ...

Regards
Mark

Alessandro Zummo wrote:
> On Tue, 14 Oct 2008 09:05:18 +0100
> Mark Jackson <mpfj@mimc.co.uk> wrote:
> 
>  Hi Mark,
> 
>    a few notes below:
> 
>> +#include <linux/module.h>
>> +#include <linux/version.h>
>> +
>> +#include <linux/kernel.h>
>> +#include <linux/platform_device.h>
>> +#include <linux/init.h>
>> +#include <linux/rtc.h>
>> +#include <linux/spi/spi.h>
>> +#include <linux/bcd.h>
>> +#include <linux/delay.h>
> 
>  Please check that you require all of those includes.
> 
> 
>> +struct ds1390
>> +{
>> +	struct rtc_device *rtc;
>> +	u8 buf[9];	/* cmd + 8 registers */
>> +	u8 tx_buf[2];
>> +	u8 rx_buf[2];
>> +};
>> +
>> +static void ds1390_set_reg(struct device *dev, unsigned char address,
>> +				unsigned char data)
>> +{
>> +	struct spi_device *spi = to_spi_device(dev);
>> +	unsigned char buf[2];
>> +
>> +	/* MSB must be '1' to write */
>> +	buf[0] = address | 0x80;
>> +	buf[1] = data;
>> +
>> +	spi_write(spi, buf, 2);
>> +}
>> +
>> +static int ds1390_get_reg(struct device *dev, unsigned char address,
>> +				unsigned char *data)
>> +{
>> +	struct spi_device *spi = to_spi_device(dev);
>> +	struct ds1390 *chip = dev_get_drvdata(dev);
>> +	struct spi_message message;
>> +	struct spi_transfer xfer;
>> +	int status;
>> +
>> +	if (!data)
>> +		return -EINVAL;
>> +
>> +	/* Build our spi message */
>> +	spi_message_init(&message);
>> +	memset(&xfer, 0, sizeof(xfer));
>> +	xfer.len = 2;
>> +	/* Can tx_buf and rx_buf be equal? The doc in spi.h is not sure... */
>> +	xfer.tx_buf = chip->tx_buf;
>> +	xfer.rx_buf = chip->rx_buf;
> 
>  you use the same buffer a few functions below. either
>  one way or the other. please investigate with the spi subsystem maintainer.

David,

Just to double check (as per Alessandro's suggestion), is this okay use of the 
spi buffers ?

I took the code from an existing RTC driver (rtc-max6902), so I am assuming that
this code has already passed judgement.

> 
> 
>> +
>> +	/* Clear MSB to indicate read */
>> +	chip->tx_buf[0] = address & 0x7f;
>> +
>> +	spi_message_add_tail(&xfer, &message);
>> +
>> +	/* do the i/o */
>> +	status = spi_sync(spi, &message);
>> +	if (status == 0)
>> +	{
>> +		status = message.status;
>> +	}
>> +	else
>> +	{
>> +		return status;
>> +	}
> 
>  should be cleaner in this way:
> 
>  if (status != 0)
> 	return status;
> 
>  *data = chip->rx_buf[1];
> 
>  return message.status;
> 
> 
>> +static int ds1390_get_datetime(struct device *dev, struct rtc_time *dt)
>> +{
>> +	struct spi_device *spi = to_spi_device(dev);
>> +	struct ds1390 *chip = dev_get_drvdata(dev);
>> +	struct spi_message message;
>> +	struct spi_transfer xfer;
>> +	int status;
>> +
>> +	/* build the message */
>> +	spi_message_init(&message);
>> +	memset(&xfer, 0, sizeof(xfer));
>> +	xfer.len = 1 + 7;	/* read command + 7 registers */
>> +	xfer.tx_buf = chip->buf;
>> +	xfer.rx_buf = chip->buf;
> 
>  the buffer mentioned above.

... see text above ...

> 
> 
>> +	chip->buf[0] = DS1390_REG_SECONDS;
>> +	spi_message_add_tail(&xfer, &message);
>> +
>> +	/* do the i/o */
>> +	status = spi_sync(spi, &message);
>> +	if (status == 0)
>> +	{
>> +		status = message.status;
>> +	}
>> +	else
>> +	{
>> +		return status;
>> +	}
> 
>  ditto.
> 
>> +	/* The chip sends data in this order:
>> +	 * Seconds, Minutes, Hours, Day, Date, Month / Century, Year */
>> +	dt->tm_sec	= BCD2BIN(chip->buf[1]);
>> +	dt->tm_min	= BCD2BIN(chip->buf[2]);
>> +	dt->tm_hour	= BCD2BIN(chip->buf[3]);
>> +	dt->tm_wday	= BCD2BIN(chip->buf[4]);
>> +	dt->tm_mday	= BCD2BIN(chip->buf[5]);
>> +	/* mask off century bit */
>> +	dt->tm_mon	= BCD2BIN(chip->buf[6] & 0x7f) - 1;
>> +	/* adjust for century bit */
>> +	dt->tm_year = BCD2BIN(chip->buf[7]) + ((chip->buf[6] & 0x80) ? 100 : 0);
>> +
>> +	return 0;
>> +}
>> +
>> +static int ds1390_set_datetime(struct device *dev, struct rtc_time *dt)
>> +{
>> +	struct spi_device *spi = to_spi_device(dev);
>> +	struct ds1390 *chip = dev_get_drvdata(dev);
>> +	struct spi_message message;
>> +	struct spi_transfer xfer;
>> +	int status;
>> +
>> +	/* build the message */
>> +	spi_message_init(&message);
>> +	memset(&xfer, 0, sizeof(xfer));
>> +	xfer.len = 1 + 8;	/* write command + 8 registers */
>> +	xfer.tx_buf = chip->buf;
>> +	xfer.rx_buf = chip->buf;

... and I guess here as well ... ???

>> +	chip->buf[0] = DS1390_REG_SECONDS | 0x80;
>> +	chip->buf[1] = BIN2BCD(dt->tm_sec);
>> +	chip->buf[2] = BIN2BCD(dt->tm_min);
>> +	chip->buf[3] = BIN2BCD(dt->tm_hour);
>> +	chip->buf[4] = BIN2BCD(dt->tm_wday);
>> +	chip->buf[5] = BIN2BCD(dt->tm_mday);
>> +	chip->buf[6] = BIN2BCD(dt->tm_mon + 1) | ((dt->tm_year > 99) ? 0x80 : 0x00);
>> +	chip->buf[7] = BIN2BCD(dt->tm_year % 100);
>> +	spi_message_add_tail(&xfer, &message);
>> +
>> +	/* do the i/o */
>> +	status = spi_sync(spi, &message);
>> +	if (status == 0)
>> +	{
>> +		status = message.status;
>> +	}
>> +	else
>> +	{
>> +		return status;
>> +	}
> 
>  if status == 0, status is not used anymore, so you can
>  just return if != 0;
> 
>> +	return 0;
>> +}
>> +
>> +static int ds1390_read_time(struct device *dev, struct rtc_time *tm)
>> +{
>> +	return ds1390_get_datetime(dev, tm);
>> +}
>> +
>> +static int ds1390_set_time(struct device *dev, struct rtc_time *tm)
>> +{
>> +	return ds1390_set_datetime(dev, tm);
>> +}
>> +
>> +static const struct rtc_class_ops ds1390_rtc_ops = {
>> +	.read_time	= ds1390_read_time,
>> +	.set_time	= ds1390_set_time,
>> +};
>> +
>> +static int __devinit ds1390_probe(struct spi_device *spi)
>> +{
>> +	struct rtc_device *rtc;
>> +	unsigned char tmp;
>> +	struct ds1390 *chip;
>> +	int res;
>> +
>> +	printk("DS1390 SPI RTC driver\n");
>> +
>> +	rtc = rtc_device_register("ds1390",
>> +				&spi->dev, &ds1390_rtc_ops, THIS_MODULE);
>> +	if (IS_ERR(rtc))
>> +	{
>> +		printk("RTC : unable to register device\n");
>> +		return PTR_ERR(rtc);
>> +	}
>> +
>> +	spi->mode = SPI_MODE_3;
>> +	spi->bits_per_word = 8;
>> +	spi_setup(spi);
>> +
>> +	chip = kzalloc(sizeof *chip, GFP_KERNEL);
>> +	if (!chip) {
>> +		printk("RTC : unable to allocate device memory\n");
>> +		rtc_device_unregister(rtc);
>> +		return -ENOMEM;
>> +	}
>> +	chip->rtc = rtc;
>> +	dev_set_drvdata(&spi->dev, chip);
>> +
>> +	res = ds1390_get_reg(&spi->dev, DS1390_REG_SECONDS, &tmp);
>> +	if (res) {
>> +		printk("RTC : unable to read device\n");
>> +		rtc_device_unregister(rtc);
>> +		return res;
>> +	}
>> +
>> +	return 0;
>> +}
>> +
>> +static int __devexit ds1390_remove(struct spi_device *spi)
>> +{
>> +	struct ds1390 *chip = platform_get_drvdata(spi);
>> +	struct rtc_device *rtc = chip->rtc;
>> +
>> +	if (rtc)
>> +		rtc_device_unregister(rtc);
>> +
>> +	kfree(chip);
>> +
>> +	return 0;
>> +}
>> +
>> +static struct spi_driver ds1390_driver = {
>> +	.driver = {
>> +		.name	= "rtc-ds1390",
>> +		.bus	= &spi_bus_type,
>> +		.owner	= THIS_MODULE,
>> +	},
>> +	.probe	= ds1390_probe,
>> +	.remove = __devexit_p(ds1390_remove),
>> +};
>> +
>> +static __init int ds1390_init(void)
>> +{
>> +	return spi_register_driver(&ds1390_driver);
>> +}
>> +module_init(ds1390_init);
>> +
>> +static __exit void ds1390_exit(void)
>> +{
>> +	spi_unregister_driver(&ds1390_driver);
>> +}
>> +module_exit(ds1390_exit);
>> +
>> +MODULE_DESCRIPTION ("DS1390 SPI RTC driver");
>> +MODULE_AUTHOR ("Mark Jackson");
> 
>  you email here please.
> 
>> +MODULE_LICENSE ("GPL");
> 
> 

Re: [PATCH] Add Dallas DS1390 RTC chip

[David Brownell]

On Friday 17 October 2008, Mark Jackson wrote:
> >> +    /* Can tx_buf and rx_buf be equal? The doc in spi.h is not sure... */
> >> +    xfer.tx_buf = chip->tx_buf;
> >> +    xfer.rx_buf = chip->rx_buf;
> > 
> >  you use the same buffer a few functions below. either
> >  one way or the other. please investigate with the spi subsystem maintainer.
> 
> David,
> 
> Just to double check (as per Alessandro's suggestion), is this okay use of the 
> spi buffers ?

Yes.  That comment deserves to be updated.

SPI does bi-directional I/O, and the underlying controller
should be able to just replace the contents of a buffer
with a spi_transfer that uses the same rx and tx buffers.

- Dave

Re: [PATCH] Add Dallas DS1390 RTC chip

[Mark Jackson]

David Brownell wrote:
> On Friday 17 October 2008, Mark Jackson wrote:
>>>> +    /* Can tx_buf and rx_buf be equal? The doc in spi.h is not sure... */
>>>> +    xfer.tx_buf = chip->tx_buf;
>>>> +    xfer.rx_buf = chip->rx_buf;
>>>  you use the same buffer a few functions below. either
>>>  one way or the other. please investigate with the spi subsystem maintainer.
>> David,
>>
>> Just to double check (as per Alessandro's suggestion), is this okay use of the 
>> spi buffers ?
> 
> Yes.  That comment deserves to be updated.
> 
> SPI does bi-directional I/O, and the underlying controller
> should be able to just replace the contents of a buffer
> with a spi_transfer that uses the same rx and tx buffers.

Excellent.  Thanks for the confirmation.

Regards
Mark

[PATCH] Add Dallas DS1390 RTC chip

[Mark Jackson]

This patch adds support for the Dallas DS1390 SPI RTC chip.

Signed-off-by: M.Jackson <mpfj@mimc.co.uk>
---
 drivers/rtc/Kconfig      |   14 +++
 drivers/rtc/Makefile     |    1 +
 drivers/rtc/rtc-ds1390.c |  283 ++++++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 298 insertions(+), 0 deletions(-)

diff --git a/drivers/rtc/Kconfig b/drivers/rtc/Kconfig
index 9a9755c..7ec6abb 100644
--- a/drivers/rtc/Kconfig
+++ b/drivers/rtc/Kconfig
@@ -292,6 +292,20 @@ config RTC_DRV_DS1305
 	  This driver can also be built as a module. If so, the module
 	  will be called rtc-ds1305.
 
+config RTC_DRV_DS1390
+	tristate "Dallas/Maxim DS1390"
+	help
+	  If you say yes here you get support for the DS1390 and probably
+	  other chips connected with SPI.
+
+	  The first seven registers on these chips hold an RTC, and other
+	  registers may add features such as NVRAM, a trickle charger for
+	  the RTC/NVRAM backup power, and alarms.  This driver may not
+	  expose all those available chip features.
+
+	  This driver can also be built as a module. If so, the module
+	  will be called rtc-ds1390.
+
 config RTC_DRV_MAX6902
 	tristate "Maxim MAX6902"
 	help
diff --git a/drivers/rtc/Makefile b/drivers/rtc/Makefile
index 18622ef..6306900 100644
--- a/drivers/rtc/Makefile
+++ b/drivers/rtc/Makefile
@@ -27,6 +27,7 @@ obj-$(CONFIG_RTC_DRV_DS1302)	+= rtc-ds1302.o
 obj-$(CONFIG_RTC_DRV_DS1305)	+= rtc-ds1305.o
 obj-$(CONFIG_RTC_DRV_DS1307)	+= rtc-ds1307.o
 obj-$(CONFIG_RTC_DRV_DS1374)	+= rtc-ds1374.o
+obj-$(CONFIG_RTC_DRV_DS1390)	+= rtc-ds1390.o
 obj-$(CONFIG_RTC_DRV_DS1511)	+= rtc-ds1511.o
 obj-$(CONFIG_RTC_DRV_DS1553)	+= rtc-ds1553.o
 obj-$(CONFIG_RTC_DRV_DS1672)	+= rtc-ds1672.o
diff --git a/drivers/rtc/rtc-ds1390.c b/drivers/rtc/rtc-ds1390.c
new file mode 100644
index 0000000..57fb215
--- /dev/null
+++ b/drivers/rtc/rtc-ds1390.c
@@ -0,0 +1,283 @@
+/* drivers/rtc/rtc-ds1390.c
+ *
+ * Copyright (C) 2008 Mercury IMC Ltd
+ *
+ * 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.
+ *
+ * Driver for DS1390 spi RTC
+ *
+ * Changelog:
+ *
+ * 04-Apr-2008: Mark Jackson <mpfj@mimc.co.uk>
+ *		- Initial version based on rtc-max6902
+ *		- No alarm support though !!
+ */
+
+#include <linux/module.h>
+#include <linux/version.h>
+
+#include <linux/kernel.h>
+#include <linux/platform_device.h>
+#include <linux/init.h>
+#include <linux/rtc.h>
+#include <linux/spi/spi.h>
+#include <linux/bcd.h>
+#include <linux/delay.h>
+
+#define DS1390_REG_100THS		0x00
+#define DS1390_REG_SECONDS		0x01
+#define DS1390_REG_MINUTES		0x02
+#define DS1390_REG_HOURS		0x03
+#define DS1390_REG_DAY			0x04
+#define DS1390_REG_DATE			0x05
+#define DS1390_REG_MONTH_CENT		0x06
+#define DS1390_REG_YEAR			0x07
+
+#define DS1390_REG_ALARM_100THS		0x08
+#define DS1390_REG_ALARM_SECONDS	0x09
+#define DS1390_REG_ALARM_MINUTES	0x0A
+#define DS1390_REG_ALARM_HOURS		0x0B
+#define DS1390_REG_ALARM_DAY_DATE	0x0C
+
+#define DS1390_REG_CONTROL		0x0D
+#define DS1390_REG_STATUS		0x0E
+#define DS1390_REG_TRICKLE		0x0F
+
+struct ds1390
+{
+	struct rtc_device *rtc;
+	u8 buf[9];	/* cmd + 8 registers */
+	u8 tx_buf[2];
+	u8 rx_buf[2];
+};
+
+static void ds1390_set_reg(struct device *dev, unsigned char address,
+				unsigned char data)
+{
+	struct spi_device *spi = to_spi_device(dev);
+	unsigned char buf[2];
+
+	/* MSB must be '1' to write */
+	buf[0] = address | 0x80;
+	buf[1] = data;
+
+	spi_write(spi, buf, 2);
+}
+
+static int ds1390_get_reg(struct device *dev, unsigned char address,
+				unsigned char *data)
+{
+	struct spi_device *spi = to_spi_device(dev);
+	struct ds1390 *chip = dev_get_drvdata(dev);
+	struct spi_message message;
+	struct spi_transfer xfer;
+	int status;
+
+	if (!data)
+		return -EINVAL;
+
+	/* Build our spi message */
+	spi_message_init(&message);
+	memset(&xfer, 0, sizeof(xfer));
+	xfer.len = 2;
+	/* Can tx_buf and rx_buf be equal? The doc in spi.h is not sure... */
+	xfer.tx_buf = chip->tx_buf;
+	xfer.rx_buf = chip->rx_buf;
+
+	/* Clear MSB to indicate read */
+	chip->tx_buf[0] = address & 0x7f;
+
+	spi_message_add_tail(&xfer, &message);
+
+	/* do the i/o */
+	status = spi_sync(spi, &message);
+	if (status == 0)
+	{
+		status = message.status;
+	}
+	else
+	{
+		return status;
+	}
+
+	*data = chip->rx_buf[1];
+
+	return status;
+}
+
+static int ds1390_get_datetime(struct device *dev, struct rtc_time *dt)
+{
+	struct spi_device *spi = to_spi_device(dev);
+	struct ds1390 *chip = dev_get_drvdata(dev);
+	struct spi_message message;
+	struct spi_transfer xfer;
+	int status;
+
+	/* build the message */
+	spi_message_init(&message);
+	memset(&xfer, 0, sizeof(xfer));
+	xfer.len = 1 + 7;	/* read command + 7 registers */
+	xfer.tx_buf = chip->buf;
+	xfer.rx_buf = chip->buf;
+	chip->buf[0] = DS1390_REG_SECONDS;
+	spi_message_add_tail(&xfer, &message);
+
+	/* do the i/o */
+	status = spi_sync(spi, &message);
+	if (status == 0)
+	{
+		status = message.status;
+	}
+	else
+	{
+		return status;
+	}
+
+	/* The chip sends data in this order:
+	 * Seconds, Minutes, Hours, Day, Date, Month / Century, Year */
+	dt->tm_sec	= BCD2BIN(chip->buf[1]);
+	dt->tm_min	= BCD2BIN(chip->buf[2]);
+	dt->tm_hour	= BCD2BIN(chip->buf[3]);
+	dt->tm_wday	= BCD2BIN(chip->buf[4]);
+	dt->tm_mday	= BCD2BIN(chip->buf[5]);
+	/* mask off century bit */
+	dt->tm_mon	= BCD2BIN(chip->buf[6] & 0x7f) - 1;
+	/* adjust for century bit */
+	dt->tm_year = BCD2BIN(chip->buf[7]) + ((chip->buf[6] & 0x80) ? 100 : 0);
+
+	return 0;
+}
+
+static int ds1390_set_datetime(struct device *dev, struct rtc_time *dt)
+{
+	struct spi_device *spi = to_spi_device(dev);
+	struct ds1390 *chip = dev_get_drvdata(dev);
+	struct spi_message message;
+	struct spi_transfer xfer;
+	int status;
+
+	/* build the message */
+	spi_message_init(&message);
+	memset(&xfer, 0, sizeof(xfer));
+	xfer.len = 1 + 8;	/* write command + 8 registers */
+	xfer.tx_buf = chip->buf;
+	xfer.rx_buf = chip->buf;
+	chip->buf[0] = DS1390_REG_SECONDS | 0x80;
+	chip->buf[1] = BIN2BCD(dt->tm_sec);
+	chip->buf[2] = BIN2BCD(dt->tm_min);
+	chip->buf[3] = BIN2BCD(dt->tm_hour);
+	chip->buf[4] = BIN2BCD(dt->tm_wday);
+	chip->buf[5] = BIN2BCD(dt->tm_mday);
+	chip->buf[6] = BIN2BCD(dt->tm_mon + 1) | ((dt->tm_year > 99) ? 0x80 : 0x00);
+	chip->buf[7] = BIN2BCD(dt->tm_year % 100);
+	spi_message_add_tail(&xfer, &message);
+
+	/* do the i/o */
+	status = spi_sync(spi, &message);
+	if (status == 0)
+	{
+		status = message.status;
+	}
+	else
+	{
+		return status;
+	}
+
+	return 0;
+}
+
+static int ds1390_read_time(struct device *dev, struct rtc_time *tm)
+{
+	return ds1390_get_datetime(dev, tm);
+}
+
+static int ds1390_set_time(struct device *dev, struct rtc_time *tm)
+{
+	return ds1390_set_datetime(dev, tm);
+}
+
+static const struct rtc_class_ops ds1390_rtc_ops = {
+	.read_time	= ds1390_read_time,
+	.set_time	= ds1390_set_time,
+};
+
+static int __devinit ds1390_probe(struct spi_device *spi)
+{
+	struct rtc_device *rtc;
+	unsigned char tmp;
+	struct ds1390 *chip;
+	int res;
+
+	printk("DS1390 SPI RTC driver\n");
+
+	rtc = rtc_device_register("ds1390",
+				&spi->dev, &ds1390_rtc_ops, THIS_MODULE);
+	if (IS_ERR(rtc))
+	{
+		printk("RTC : unable to register device\n");
+		return PTR_ERR(rtc);
+	}
+
+	spi->mode = SPI_MODE_3;
+	spi->bits_per_word = 8;
+	spi_setup(spi);
+
+	chip = kzalloc(sizeof *chip, GFP_KERNEL);
+	if (!chip) {
+		printk("RTC : unable to allocate device memory\n");
+		rtc_device_unregister(rtc);
+		return -ENOMEM;
+	}
+	chip->rtc = rtc;
+	dev_set_drvdata(&spi->dev, chip);
+
+	res = ds1390_get_reg(&spi->dev, DS1390_REG_SECONDS, &tmp);
+	if (res) {
+		printk("RTC : unable to read device\n");
+		rtc_device_unregister(rtc);
+		return res;
+	}
+
+	return 0;
+}
+
+static int __devexit ds1390_remove(struct spi_device *spi)
+{
+	struct ds1390 *chip = platform_get_drvdata(spi);
+	struct rtc_device *rtc = chip->rtc;
+
+	if (rtc)
+		rtc_device_unregister(rtc);
+
+	kfree(chip);
+
+	return 0;
+}
+
+static struct spi_driver ds1390_driver = {
+	.driver = {
+		.name	= "rtc-ds1390",
+		.bus	= &spi_bus_type,
+		.owner	= THIS_MODULE,
+	},
+	.probe	= ds1390_probe,
+	.remove = __devexit_p(ds1390_remove),
+};
+
+static __init int ds1390_init(void)
+{
+	return spi_register_driver(&ds1390_driver);
+}
+module_init(ds1390_init);
+
+static __exit void ds1390_exit(void)
+{
+	spi_unregister_driver(&ds1390_driver);
+}
+module_exit(ds1390_exit);
+
+MODULE_DESCRIPTION ("DS1390 SPI RTC driver");
+MODULE_AUTHOR ("Mark Jackson");
+MODULE_LICENSE ("GPL");