Patchwork Add Dallas DS2404 driver

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Submitter Sven Schnelle
Date April 28, 2012, 4:22 p.m.
Message ID <1335630161-15509-1-git-send-email-svens@stackframe.org>
Download mbox | patch
Permalink /patch/155672/
State New
Headers show

Comments

Sven Schnelle - April 28, 2012, 4:22 p.m.
Signed-off-by: Sven Schnelle <svens@stackframe.org>
---
 drivers/rtc/Kconfig        |    9 ++
 drivers/rtc/Makefile       |    1 +
 drivers/rtc/rtc-ds2404.c   |  305 ++++++++++++++++++++++++++++++++++++++++++++
 include/linux/rtc-ds2404.h |   20 +++
 4 files changed, 335 insertions(+)
 create mode 100644 drivers/rtc/rtc-ds2404.c
 create mode 100644 include/linux/rtc-ds2404.h
Andrew Morton - Aug. 14, 2012, 11:04 p.m.
On Sat, 28 Apr 2012 18:22:41 +0200
Sven Schnelle <svens@stackframe.org> wrote:

> Signed-off-by: Sven Schnelle <svens@stackframe.org>
> ---
>  drivers/rtc/Kconfig        |    9 ++
>  drivers/rtc/Makefile       |    1 +
>  drivers/rtc/rtc-ds2404.c   |  305 ++++++++++++++++++++++++++++++++++++++++++++
>  include/linux/rtc-ds2404.h |   20 +++
>  4 files changed, 335 insertions(+)
>  create mode 100644 drivers/rtc/rtc-ds2404.c
>  create mode 100644 include/linux/rtc-ds2404.h
> 
> diff --git a/drivers/rtc/Kconfig b/drivers/rtc/Kconfig
> index 4941cad..ae81b7a 100644
> --- a/drivers/rtc/Kconfig
> +++ b/drivers/rtc/Kconfig
> @@ -628,6 +628,15 @@ config RTC_DRV_V3020
>  	  This driver can also be built as a module. If so, the module
>  	  will be called rtc-v3020.
>  
> +config RTC_DRV_DS2404
> +	tristate "Dallas DS2404"

Should we have a "depends on GPIOLIB" here?  There doesn't seem a lot
of point in offering the driver if the gpio code isn't available?
Wolfram Sang - Aug. 15, 2012, 8:43 a.m.
Hi,

thanks for the submission. First review:

On Sat, Apr 28, 2012 at 06:22:41PM +0200, Sven Schnelle wrote:
> Signed-off-by: Sven Schnelle <svens@stackframe.org>
> ---
>  drivers/rtc/Kconfig        |    9 ++
>  drivers/rtc/Makefile       |    1 +
>  drivers/rtc/rtc-ds2404.c   |  305 ++++++++++++++++++++++++++++++++++++++++++++
>  include/linux/rtc-ds2404.h |   20 +++
>  4 files changed, 335 insertions(+)
>  create mode 100644 drivers/rtc/rtc-ds2404.c
>  create mode 100644 include/linux/rtc-ds2404.h
> 
> diff --git a/drivers/rtc/Kconfig b/drivers/rtc/Kconfig
> index 4941cad..ae81b7a 100644
> --- a/drivers/rtc/Kconfig
> +++ b/drivers/rtc/Kconfig
> @@ -628,6 +628,15 @@ config RTC_DRV_V3020
>  	  This driver can also be built as a module. If so, the module
>  	  will be called rtc-v3020.
>  
> +config RTC_DRV_DS2404
> +	tristate "Dallas DS2404"
> +	help
> +	  If you say yes here you get support for the
> +	  Dallas DS2404 RTC chip.
> +
> +	  This driver can also be built as a module. If so, the module
> +	  will be called rtc-ds2404.
> +
>  config RTC_DRV_WM831X
>  	tristate "Wolfson Microelectronics WM831x RTC"
>  	depends on MFD_WM831X
> diff --git a/drivers/rtc/Makefile b/drivers/rtc/Makefile
> index 2afdaf3..19be60f 100644
> --- a/drivers/rtc/Makefile
> +++ b/drivers/rtc/Makefile
> @@ -42,6 +42,7 @@ obj-$(CONFIG_RTC_DRV_DS1511)	+= rtc-ds1511.o
>  obj-$(CONFIG_RTC_DRV_DS1553)	+= rtc-ds1553.o
>  obj-$(CONFIG_RTC_DRV_DS1672)	+= rtc-ds1672.o
>  obj-$(CONFIG_RTC_DRV_DS1742)	+= rtc-ds1742.o
> +obj-$(CONFIG_RTC_DRV_DS2404)    += rtc-ds2404.o

Please use a tab here.

>  obj-$(CONFIG_RTC_DRV_DS3232)	+= rtc-ds3232.o
>  obj-$(CONFIG_RTC_DRV_DS3234)	+= rtc-ds3234.o
>  obj-$(CONFIG_RTC_DRV_EFI)	+= rtc-efi.o
> diff --git a/drivers/rtc/rtc-ds2404.c b/drivers/rtc/rtc-ds2404.c
> new file mode 100644
> index 0000000..0ae5a23
> --- /dev/null
> +++ b/drivers/rtc/rtc-ds2404.c
> @@ -0,0 +1,305 @@
> +/*
> + * Copyright (C) 2012 Sven Schnelle <svens@stackframe.org>
> + *
> + * 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.

Looking at at the structure of this driver, did you use rtc-v3020.c as a
template? If so, please note this here.

> + *
> + */
> +
> +#include <linux/platform_device.h>
> +#include <linux/module.h>
> +#include <linux/init.h>
> +#include <linux/rtc.h>
> +#include <linux/types.h>
> +#include <linux/bcd.h>
> +#include <linux/rtc-ds2404.h>
> +#include <linux/delay.h>
> +#include <linux/gpio.h>
> +#include <linux/slab.h>
> +
> +#include <linux/io.h>
> +
> +#define DEBUG

Should not be default?

> +
> +#define DS2404_STATUS_REG 0x200
> +#define DS2404_CONTROL_REG 0x201
> +#define DS2404_RTC_REG 0x202
> +
> +#define DS2404_WRITE_SCRATCHPAD_CMD 0x0f
> +#define DS2404_READ_SCRATCHPAD_CMD 0xaa
> +#define DS2404_COPY_SCRATCHPAD_CMD 0x55
> +#define DS2404_READ_MEMORY_CMD 0xf0
> +
> +struct ds2404;
> +
> +struct ds2404_chip_ops {
> +	int (*map_io)(struct ds2404 *chip, struct platform_device *pdev,
> +		      struct ds2404_platform_data *pdata);
> +	void (*unmap_io)(struct ds2404 *chip);
> +};

Do we really need this? AFAICS this is not enough prepraration for later
1wire support anyhow, so I'd suggest to drop the chip_ops for now and
use the functions directly until someone can properly implement and test
the 1wire addition.

> +
> +#define DS2404_RST	0
> +#define DS2404_CLK	1
> +#define DS2404_DQ	2
> +
> +struct ds2404_gpio {
> +	const char *name;
> +	unsigned int gpio;
> +};
> +
> +struct ds2404 {
> +	struct ds2404_gpio *gpio;
> +	struct ds2404_chip_ops *ops;
> +	struct rtc_device *rtc;
> +};
> +
> +static struct ds2404_gpio ds2404_gpio[] = {
> +	{ "RTC RST", 0 },
> +	{ "RTC CLK", 0 },
> +	{ "RTC DQ", 0 },

Add DS2404 to the names?

> +};
> +
> +static int ds2404_gpio_map(struct ds2404 *chip, struct platform_device *pdev,
> +			  struct ds2404_platform_data *pdata)
> +{
> +	int i, err;
> +
> +	ds2404_gpio[DS2404_RST].gpio = pdata->gpio_rst;
> +	ds2404_gpio[DS2404_CLK].gpio = pdata->gpio_clk;
> +	ds2404_gpio[DS2404_DQ].gpio = pdata->gpio_dq;
> +
> +	for (i = 0; i < ARRAY_SIZE(ds2404_gpio); i++) {

gpio_request_array?

> +		err = gpio_request(ds2404_gpio[i].gpio, ds2404_gpio[i].name);
> +		if (err) {
> +			printk(KERN_ERR "error mapping gpio %s: %d\n",
> +				ds2404_gpio[i].name, err);
> +			goto err_request;
> +		}
> +		if (i != DS2404_DQ)
> +			gpio_direction_output(ds2404_gpio[i].gpio, 1);
> +	}
> +
> +	chip->gpio = ds2404_gpio;
> +	return 0;
> +
> +err_request:
> +	while (--i >= 0)
> +		gpio_free(ds2404_gpio[i].gpio);
> +	return err;
> +}
> +
> +static void ds2404_gpio_unmap(struct ds2404 *chip)
> +{
> +	int i;
> +
> +	for (i = 0; i < ARRAY_SIZE(ds2404_gpio); i++)
> +		gpio_free(ds2404_gpio[i].gpio);
> +}
> +
> +static struct ds2404_chip_ops ds2404_gpio_ops = {
> +	.map_io		= ds2404_gpio_map,
> +	.unmap_io	= ds2404_gpio_unmap,
> +};
> +
> +static void ds2404_reset(struct device *dev)
> +{
> +	gpio_set_value(ds2404_gpio[DS2404_RST].gpio, 0);
> +	udelay(1000);
> +	gpio_set_value(ds2404_gpio[DS2404_RST].gpio, 1);
> +	gpio_set_value(ds2404_gpio[DS2404_CLK].gpio, 0);
> +	gpio_direction_output(ds2404_gpio[DS2404_DQ].gpio, 0);
> +	udelay(10);
> +}
> +
> +static void ds2404_write_byte(struct device *dev, u8 byte)
> +{
> +	int i;
> +
> +	gpio_direction_output(ds2404_gpio[DS2404_DQ].gpio, 1);
> +	for (i = 0; i < 8; i++) {
> +		gpio_set_value(ds2404_gpio[DS2404_DQ].gpio, byte & (1 << i));
> +		udelay(10);
> +		gpio_set_value(ds2404_gpio[DS2404_CLK].gpio, 1);
> +		udelay(10);
> +		gpio_set_value(ds2404_gpio[DS2404_CLK].gpio, 0);
> +		udelay(10);
> +	}
> +}
> +
> +static u8 ds2404_read_byte(struct device *dev)
> +{
> +	int i;
> +	u8 ret = 0;
> +
> +	gpio_direction_input(ds2404_gpio[DS2404_DQ].gpio);
> +
> +	for (i = 0; i < 8; i++) {
> +		gpio_set_value(ds2404_gpio[DS2404_CLK].gpio, 0);
> +		udelay(10);
> +		if (gpio_get_value(ds2404_gpio[DS2404_DQ].gpio))
> +			ret |= 1 << i;
> +		gpio_set_value(ds2404_gpio[DS2404_CLK].gpio, 1);
> +		udelay(10);
> +	}
> +	return ret;
> +}
> +
> +static void ds2404_read_memory(struct device *dev, u16 offset,
> +			       int length, u8 *out)
> +{
> +	ds2404_reset(dev);
> +	ds2404_write_byte(dev, DS2404_READ_MEMORY_CMD);
> +	ds2404_write_byte(dev, offset & 0xff);
> +	ds2404_write_byte(dev, (offset >> 8) & 0xff);
> +	while (length--)
> +		*out++ = ds2404_read_byte(dev);
> +}
> +
> +static void ds2404_write_memory(struct device *dev, u16 offset,
> +				int length, u8 *out)
> +{
> +	int i;
> +	u8 ta01, ta02, es;
> +
> +	ds2404_reset(dev);
> +	ds2404_write_byte(dev, DS2404_WRITE_SCRATCHPAD_CMD);
> +	ds2404_write_byte(dev, offset & 0xff);
> +	ds2404_write_byte(dev, (offset >> 8) & 0xff);
> +
> +	for (i = 0; i < length; i++)
> +		ds2404_write_byte(dev, out[i]);
> +
> +	ds2404_reset(dev);
> +	ds2404_write_byte(dev, DS2404_READ_SCRATCHPAD_CMD);
> +
> +	ta01 = ds2404_read_byte(dev);
> +	ta02 = ds2404_read_byte(dev);
> +	es = ds2404_read_byte(dev);
> +
> +	for (i = 0; i < length; i++) {
> +		if (out[i] != ds2404_read_byte(dev)) {
> +			printk(KERN_ERR "read invalid data\n");
> +			return;
> +		}
> +	}
> +
> +	ds2404_reset(dev);
> +	ds2404_write_byte(dev, DS2404_COPY_SCRATCHPAD_CMD);
> +	ds2404_write_byte(dev, ta01);
> +	ds2404_write_byte(dev, ta02);
> +	ds2404_write_byte(dev, es);
> +
> +	gpio_direction_input(ds2404_gpio[DS2404_DQ].gpio);
> +	while (gpio_get_value(ds2404_gpio[DS2404_DQ].gpio))
> +		;
> +}
> +
> +static void ds2404_enable_osc(struct device *dev)
> +{
> +	u8 in[1] = { 0x10 }; /* enable oscillator */
> +	ds2404_write_memory(dev, 0x201, 1, in);
> +}
> +
> +static int ds2404_read_time(struct device *dev, struct rtc_time *dt)
> +{
> +	unsigned long time = 0;
> +
> +	ds2404_read_memory(dev, 0x203, 4, (u8 *)&time);
> +	time = le32_to_cpu(time);
> +
> +	rtc_time_to_tm(time, dt);
> +	return rtc_valid_tm(dt);
> +}
> +
> +static int ds2404_set_mmss(struct device *dev, unsigned long secs)
> +{
> +	u32 time = cpu_to_le32(secs);
> +	ds2404_write_memory(dev, 0x203, 4, (u8 *)&time);
> +	return 0;
> +}
> +
> +static const struct rtc_class_ops ds2404_rtc_ops = {
> +	.read_time	= ds2404_read_time,
> +	.set_mmss	= ds2404_set_mmss,
> +};
> +
> +static int rtc_probe(struct platform_device *pdev)
> +{
> +	struct ds2404_platform_data *pdata = pdev->dev.platform_data;
> +	struct ds2404 *chip;
> +	int retval = -EBUSY;
> +
> +	chip = kzalloc(sizeof(struct ds2404), GFP_KERNEL);
> +	if (!chip)
> +		return -ENOMEM;
> +
> +	chip->ops = &ds2404_gpio_ops;
> +
> +	retval = chip->ops->map_io(chip, pdev, pdata);
> +	if (retval)
> +		goto err_chip;
> +
> +	dev_info(&pdev->dev, "using GPIOs RST:%d, CLK:%d, DQ:%d\n",
> +		 chip->gpio[DS2404_RST].gpio, chip->gpio[DS2404_CLK].gpio,
> +		 chip->gpio[DS2404_DQ].gpio);
> +
> +	platform_set_drvdata(pdev, chip);
> +
> +	chip->rtc = rtc_device_register("ds2404",
> +				&pdev->dev, &ds2404_rtc_ops, THIS_MODULE);
> +	if (IS_ERR(chip->rtc)) {
> +		retval = PTR_ERR(chip->rtc);
> +		goto err_io;
> +	}
> +
> +	ds2404_enable_osc(&pdev->dev);
> +	return 0;
> +
> +err_io:
> +	chip->ops->unmap_io(chip);
> +err_chip:
> +	kfree(chip);
> +	return retval;
> +}
> +
> +static int rtc_remove(struct platform_device *dev)
> +{
> +	struct ds2404 *chip = platform_get_drvdata(dev);
> +	struct rtc_device *rtc = chip->rtc;
> +
> +	if (rtc)
> +		rtc_device_unregister(rtc);
> +
> +	chip->ops->unmap_io(chip);
> +	kfree(chip);
> +
> +	return 0;
> +}
> +
> +static struct platform_driver rtc_device_driver = {
> +	.probe	= rtc_probe,
> +	.remove = rtc_remove,
> +	.driver = {
> +		.name	= "ds2404",
> +		.owner	= THIS_MODULE,
> +	},
> +};
> +
> +static __init int ds2404_init(void)
> +{
> +	return platform_driver_register(&rtc_device_driver);
> +}
> +
> +static __exit void ds2404_exit(void)
> +{
> +	platform_driver_unregister(&rtc_device_driver);
> +}
> +
> +module_init(ds2404_init);
> +module_exit(ds2404_exit);

module_platform_driver macro?

> +
> +MODULE_DESCRIPTION("DS2404 RTC");
> +MODULE_AUTHOR("Sven Schnelle");

Please add an email address.

> +MODULE_LICENSE("GPL");
> +MODULE_ALIAS("platform:ds2404");
> diff --git a/include/linux/rtc-ds2404.h b/include/linux/rtc-ds2404.h
> new file mode 100644
> index 0000000..22c5382
> --- /dev/null
> +++ b/include/linux/rtc-ds2404.h
> @@ -0,0 +1,20 @@
> +/*
> + * ds2404.h - platform data structure for the DS2404 RTC.
> + *
> + * This file is subject to the terms and conditions of the GNU General Public
> + * License.  See the file "COPYING" in the main directory of this archive
> + * for more details.
> + *
> + * Copyright (C) 2012 Sven Schnelle <svens@stackframe.org>
> + */
> +
> +#ifndef __LINUX_DS2404_H
> +#define __LINUX_DS2404_H
> +
> +struct ds2404_platform_data {
> +
> +	unsigned int gpio_rst;
> +	unsigned int gpio_clk;
> +	unsigned int gpio_dq;
> +};
> +#endif
> -- 
> 1.7.10
> 
> -- 
> You received this message because you are subscribed to "rtc-linux".
> Membership options at http://groups.google.com/group/rtc-linux .
> Please read http://groups.google.com/group/rtc-linux/web/checklist
> before submitting a driver.

Patch

diff --git a/drivers/rtc/Kconfig b/drivers/rtc/Kconfig
index 4941cad..ae81b7a 100644
--- a/drivers/rtc/Kconfig
+++ b/drivers/rtc/Kconfig
@@ -628,6 +628,15 @@  config RTC_DRV_V3020
 	  This driver can also be built as a module. If so, the module
 	  will be called rtc-v3020.
 
+config RTC_DRV_DS2404
+	tristate "Dallas DS2404"
+	help
+	  If you say yes here you get support for the
+	  Dallas DS2404 RTC chip.
+
+	  This driver can also be built as a module. If so, the module
+	  will be called rtc-ds2404.
+
 config RTC_DRV_WM831X
 	tristate "Wolfson Microelectronics WM831x RTC"
 	depends on MFD_WM831X
diff --git a/drivers/rtc/Makefile b/drivers/rtc/Makefile
index 2afdaf3..19be60f 100644
--- a/drivers/rtc/Makefile
+++ b/drivers/rtc/Makefile
@@ -42,6 +42,7 @@  obj-$(CONFIG_RTC_DRV_DS1511)	+= rtc-ds1511.o
 obj-$(CONFIG_RTC_DRV_DS1553)	+= rtc-ds1553.o
 obj-$(CONFIG_RTC_DRV_DS1672)	+= rtc-ds1672.o
 obj-$(CONFIG_RTC_DRV_DS1742)	+= rtc-ds1742.o
+obj-$(CONFIG_RTC_DRV_DS2404)    += rtc-ds2404.o
 obj-$(CONFIG_RTC_DRV_DS3232)	+= rtc-ds3232.o
 obj-$(CONFIG_RTC_DRV_DS3234)	+= rtc-ds3234.o
 obj-$(CONFIG_RTC_DRV_EFI)	+= rtc-efi.o
diff --git a/drivers/rtc/rtc-ds2404.c b/drivers/rtc/rtc-ds2404.c
new file mode 100644
index 0000000..0ae5a23
--- /dev/null
+++ b/drivers/rtc/rtc-ds2404.c
@@ -0,0 +1,305 @@ 
+/*
+ * Copyright (C) 2012 Sven Schnelle <svens@stackframe.org>
+ *
+ * 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/platform_device.h>
+#include <linux/module.h>
+#include <linux/init.h>
+#include <linux/rtc.h>
+#include <linux/types.h>
+#include <linux/bcd.h>
+#include <linux/rtc-ds2404.h>
+#include <linux/delay.h>
+#include <linux/gpio.h>
+#include <linux/slab.h>
+
+#include <linux/io.h>
+
+#define DEBUG
+
+#define DS2404_STATUS_REG 0x200
+#define DS2404_CONTROL_REG 0x201
+#define DS2404_RTC_REG 0x202
+
+#define DS2404_WRITE_SCRATCHPAD_CMD 0x0f
+#define DS2404_READ_SCRATCHPAD_CMD 0xaa
+#define DS2404_COPY_SCRATCHPAD_CMD 0x55
+#define DS2404_READ_MEMORY_CMD 0xf0
+
+struct ds2404;
+
+struct ds2404_chip_ops {
+	int (*map_io)(struct ds2404 *chip, struct platform_device *pdev,
+		      struct ds2404_platform_data *pdata);
+	void (*unmap_io)(struct ds2404 *chip);
+};
+
+#define DS2404_RST	0
+#define DS2404_CLK	1
+#define DS2404_DQ	2
+
+struct ds2404_gpio {
+	const char *name;
+	unsigned int gpio;
+};
+
+struct ds2404 {
+	struct ds2404_gpio *gpio;
+	struct ds2404_chip_ops *ops;
+	struct rtc_device *rtc;
+};
+
+static struct ds2404_gpio ds2404_gpio[] = {
+	{ "RTC RST", 0 },
+	{ "RTC CLK", 0 },
+	{ "RTC DQ", 0 },
+};
+
+static int ds2404_gpio_map(struct ds2404 *chip, struct platform_device *pdev,
+			  struct ds2404_platform_data *pdata)
+{
+	int i, err;
+
+	ds2404_gpio[DS2404_RST].gpio = pdata->gpio_rst;
+	ds2404_gpio[DS2404_CLK].gpio = pdata->gpio_clk;
+	ds2404_gpio[DS2404_DQ].gpio = pdata->gpio_dq;
+
+	for (i = 0; i < ARRAY_SIZE(ds2404_gpio); i++) {
+		err = gpio_request(ds2404_gpio[i].gpio, ds2404_gpio[i].name);
+		if (err) {
+			printk(KERN_ERR "error mapping gpio %s: %d\n",
+				ds2404_gpio[i].name, err);
+			goto err_request;
+		}
+		if (i != DS2404_DQ)
+			gpio_direction_output(ds2404_gpio[i].gpio, 1);
+	}
+
+	chip->gpio = ds2404_gpio;
+	return 0;
+
+err_request:
+	while (--i >= 0)
+		gpio_free(ds2404_gpio[i].gpio);
+	return err;
+}
+
+static void ds2404_gpio_unmap(struct ds2404 *chip)
+{
+	int i;
+
+	for (i = 0; i < ARRAY_SIZE(ds2404_gpio); i++)
+		gpio_free(ds2404_gpio[i].gpio);
+}
+
+static struct ds2404_chip_ops ds2404_gpio_ops = {
+	.map_io		= ds2404_gpio_map,
+	.unmap_io	= ds2404_gpio_unmap,
+};
+
+static void ds2404_reset(struct device *dev)
+{
+	gpio_set_value(ds2404_gpio[DS2404_RST].gpio, 0);
+	udelay(1000);
+	gpio_set_value(ds2404_gpio[DS2404_RST].gpio, 1);
+	gpio_set_value(ds2404_gpio[DS2404_CLK].gpio, 0);
+	gpio_direction_output(ds2404_gpio[DS2404_DQ].gpio, 0);
+	udelay(10);
+}
+
+static void ds2404_write_byte(struct device *dev, u8 byte)
+{
+	int i;
+
+	gpio_direction_output(ds2404_gpio[DS2404_DQ].gpio, 1);
+	for (i = 0; i < 8; i++) {
+		gpio_set_value(ds2404_gpio[DS2404_DQ].gpio, byte & (1 << i));
+		udelay(10);
+		gpio_set_value(ds2404_gpio[DS2404_CLK].gpio, 1);
+		udelay(10);
+		gpio_set_value(ds2404_gpio[DS2404_CLK].gpio, 0);
+		udelay(10);
+	}
+}
+
+static u8 ds2404_read_byte(struct device *dev)
+{
+	int i;
+	u8 ret = 0;
+
+	gpio_direction_input(ds2404_gpio[DS2404_DQ].gpio);
+
+	for (i = 0; i < 8; i++) {
+		gpio_set_value(ds2404_gpio[DS2404_CLK].gpio, 0);
+		udelay(10);
+		if (gpio_get_value(ds2404_gpio[DS2404_DQ].gpio))
+			ret |= 1 << i;
+		gpio_set_value(ds2404_gpio[DS2404_CLK].gpio, 1);
+		udelay(10);
+	}
+	return ret;
+}
+
+static void ds2404_read_memory(struct device *dev, u16 offset,
+			       int length, u8 *out)
+{
+	ds2404_reset(dev);
+	ds2404_write_byte(dev, DS2404_READ_MEMORY_CMD);
+	ds2404_write_byte(dev, offset & 0xff);
+	ds2404_write_byte(dev, (offset >> 8) & 0xff);
+	while (length--)
+		*out++ = ds2404_read_byte(dev);
+}
+
+static void ds2404_write_memory(struct device *dev, u16 offset,
+				int length, u8 *out)
+{
+	int i;
+	u8 ta01, ta02, es;
+
+	ds2404_reset(dev);
+	ds2404_write_byte(dev, DS2404_WRITE_SCRATCHPAD_CMD);
+	ds2404_write_byte(dev, offset & 0xff);
+	ds2404_write_byte(dev, (offset >> 8) & 0xff);
+
+	for (i = 0; i < length; i++)
+		ds2404_write_byte(dev, out[i]);
+
+	ds2404_reset(dev);
+	ds2404_write_byte(dev, DS2404_READ_SCRATCHPAD_CMD);
+
+	ta01 = ds2404_read_byte(dev);
+	ta02 = ds2404_read_byte(dev);
+	es = ds2404_read_byte(dev);
+
+	for (i = 0; i < length; i++) {
+		if (out[i] != ds2404_read_byte(dev)) {
+			printk(KERN_ERR "read invalid data\n");
+			return;
+		}
+	}
+
+	ds2404_reset(dev);
+	ds2404_write_byte(dev, DS2404_COPY_SCRATCHPAD_CMD);
+	ds2404_write_byte(dev, ta01);
+	ds2404_write_byte(dev, ta02);
+	ds2404_write_byte(dev, es);
+
+	gpio_direction_input(ds2404_gpio[DS2404_DQ].gpio);
+	while (gpio_get_value(ds2404_gpio[DS2404_DQ].gpio))
+		;
+}
+
+static void ds2404_enable_osc(struct device *dev)
+{
+	u8 in[1] = { 0x10 }; /* enable oscillator */
+	ds2404_write_memory(dev, 0x201, 1, in);
+}
+
+static int ds2404_read_time(struct device *dev, struct rtc_time *dt)
+{
+	unsigned long time = 0;
+
+	ds2404_read_memory(dev, 0x203, 4, (u8 *)&time);
+	time = le32_to_cpu(time);
+
+	rtc_time_to_tm(time, dt);
+	return rtc_valid_tm(dt);
+}
+
+static int ds2404_set_mmss(struct device *dev, unsigned long secs)
+{
+	u32 time = cpu_to_le32(secs);
+	ds2404_write_memory(dev, 0x203, 4, (u8 *)&time);
+	return 0;
+}
+
+static const struct rtc_class_ops ds2404_rtc_ops = {
+	.read_time	= ds2404_read_time,
+	.set_mmss	= ds2404_set_mmss,
+};
+
+static int rtc_probe(struct platform_device *pdev)
+{
+	struct ds2404_platform_data *pdata = pdev->dev.platform_data;
+	struct ds2404 *chip;
+	int retval = -EBUSY;
+
+	chip = kzalloc(sizeof(struct ds2404), GFP_KERNEL);
+	if (!chip)
+		return -ENOMEM;
+
+	chip->ops = &ds2404_gpio_ops;
+
+	retval = chip->ops->map_io(chip, pdev, pdata);
+	if (retval)
+		goto err_chip;
+
+	dev_info(&pdev->dev, "using GPIOs RST:%d, CLK:%d, DQ:%d\n",
+		 chip->gpio[DS2404_RST].gpio, chip->gpio[DS2404_CLK].gpio,
+		 chip->gpio[DS2404_DQ].gpio);
+
+	platform_set_drvdata(pdev, chip);
+
+	chip->rtc = rtc_device_register("ds2404",
+				&pdev->dev, &ds2404_rtc_ops, THIS_MODULE);
+	if (IS_ERR(chip->rtc)) {
+		retval = PTR_ERR(chip->rtc);
+		goto err_io;
+	}
+
+	ds2404_enable_osc(&pdev->dev);
+	return 0;
+
+err_io:
+	chip->ops->unmap_io(chip);
+err_chip:
+	kfree(chip);
+	return retval;
+}
+
+static int rtc_remove(struct platform_device *dev)
+{
+	struct ds2404 *chip = platform_get_drvdata(dev);
+	struct rtc_device *rtc = chip->rtc;
+
+	if (rtc)
+		rtc_device_unregister(rtc);
+
+	chip->ops->unmap_io(chip);
+	kfree(chip);
+
+	return 0;
+}
+
+static struct platform_driver rtc_device_driver = {
+	.probe	= rtc_probe,
+	.remove = rtc_remove,
+	.driver = {
+		.name	= "ds2404",
+		.owner	= THIS_MODULE,
+	},
+};
+
+static __init int ds2404_init(void)
+{
+	return platform_driver_register(&rtc_device_driver);
+}
+
+static __exit void ds2404_exit(void)
+{
+	platform_driver_unregister(&rtc_device_driver);
+}
+
+module_init(ds2404_init);
+module_exit(ds2404_exit);
+
+MODULE_DESCRIPTION("DS2404 RTC");
+MODULE_AUTHOR("Sven Schnelle");
+MODULE_LICENSE("GPL");
+MODULE_ALIAS("platform:ds2404");
diff --git a/include/linux/rtc-ds2404.h b/include/linux/rtc-ds2404.h
new file mode 100644
index 0000000..22c5382
--- /dev/null
+++ b/include/linux/rtc-ds2404.h
@@ -0,0 +1,20 @@ 
+/*
+ * ds2404.h - platform data structure for the DS2404 RTC.
+ *
+ * This file is subject to the terms and conditions of the GNU General Public
+ * License.  See the file "COPYING" in the main directory of this archive
+ * for more details.
+ *
+ * Copyright (C) 2012 Sven Schnelle <svens@stackframe.org>
+ */
+
+#ifndef __LINUX_DS2404_H
+#define __LINUX_DS2404_H
+
+struct ds2404_platform_data {
+
+	unsigned int gpio_rst;
+	unsigned int gpio_clk;
+	unsigned int gpio_dq;
+};
+#endif