Re: [PATCH] Add driver for Dallas DS1682 elapsed time recorder

[Jean Delvare <khali@linux-fr.org>]

Hi Grant,

On Sun, 13 May 2007 01:43:42 -0600, Grant Likely wrote:
> Signed-off-by: Grant Likely <grant.likely@secretlab.ca>
> ---
> 
> Here is the 3rd iteration with the following changes:
> - Modified to be an i2c "new style" driver based on David Brownell's work

Can we see the corresponding architecture patch (device declaration)?

> - uses the new prototype for i2c_smbus_read_i2c_block_data() for block data
>   reads instead of a single byte at a time.
> 
>  drivers/i2c/chips/ds1682.c |  270 ++++++++++++++++++++++++++++++++++++++++++++
>  1 files changed, 270 insertions(+), 0 deletions(-)

Where have the changes to Kconfig and Makefile gone? Without them, this
patch is a no-op.

BTW, the config option shouldn't be named SENSORS_DS1682 as your
original patch had - this device isn't a sensor. It should be just
"DS1682".

> 
> diff --git a/drivers/i2c/chips/ds1682.c b/drivers/i2c/chips/ds1682.c
> new file mode 100644
> index 0000000..0a4a89e
> --- /dev/null
> +++ b/drivers/i2c/chips/ds1682.c
> @@ -0,0 +1,270 @@
> +/*
> + * Dallas Semiconductor DS1682 Elapsed Time Recorder device driver
> + *
> + * Written by: Grant Likely <grant.likely@secretlab.ca>
> + *
> + * Copyright (C) 2007 Secret Lab Technologies Ltd.
> + * Copyright (C) 2005 James Chapman <jchapman@katalix.com>
> + * Copyright (C) 2000 Russell King
> + *
> + * Derived from ds1337 real time clock device driver

Technically, this is the ds1337 driver on which James and Russell have
a copyright, not yours. I don't think there is anything left from the
code you originally copied from, BTW.

> + *
> + * 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.
> + */
> +
> +/*
> + * The DS1682 elapsed timer recorder is a simple device that implements
> + * one elapsed time counter, one event counter, an alarm signal and 10
> + * bytes of general purpose EEPROM.
> + *
> + * This driver provides access to the DS1682 counters and user data via
> + * the sysfs.  The following attributes are added to the device node:
> + *     elapsed_time (u32): Total elapsed event time in ms resolution
> + *     alarm_time (u32): When elapsed time exceeds the value in alarm_time,
> + *                       then the alarm pin is asserted.
> + *     event_count (u16): number of times the event pin has gone low.
> + *     eeprom (u8[10]): general purpose EEPROM
> + *
> + * Counter registers and user data are both read/write unless the device
> + * has been write protected.  This driver does not support turning off write
> + * protection.  Once write protection is turned on, it is impossible to
> + * turn it off again, so I have left the feature out of this driver to avoid
> + * accidental enabling, but it is trivial to add write protect support.
> + *
> + */
> +
> +#include <linux/module.h>
> +#include <linux/init.h>
> +#include <linux/slab.h>
> +#include <linux/i2c.h>
> +#include <linux/string.h>
> +#include <linux/list.h>
> +#include <linux/sysfs.h>
> +#include <linux/ctype.h>
> +#include <linux/hwmon-sysfs.h>
> +
> +/* Device registers */
> +#define DS1682_REG_CONFIG		0x00
> +#define DS1682_REG_ALARM		0x01
> +#define DS1682_REG_ELAPSED		0x05
> +#define DS1682_REG_EVT_CNTR		0x09
> +#define DS1682_REG_EEPROM		0x0b
> +#define DS1682_REG_RESET		0x1d
> +#define DS1682_REG_WRITE_DISABLE	0x1e
> +#define DS1682_REG_WRITE_MEM_DISABLE	0x1f
> +
> +#define DS1682_EEPROM_SIZE		10
> +
> +/*
> + * Generic counter attributes
> + */
> +static ssize_t ds1682_show(struct device *dev, struct device_attribute *attr,
> +			   char *buf)
> +{
> +	struct sensor_device_attribute_2 *sattr = to_sensor_dev_attr_2(attr);
> +	struct i2c_client *client = to_i2c_client(dev);
> +	__le32 val = 0;
> +	int rc;
> +
> +	dev_dbg(dev, "ds1682_show() called on %s\n", attr->attr.name);
> +
> +	/* Read the register */
> +	rc = i2c_smbus_read_i2c_block_data(client, sattr->index, sattr->nr,
> +					   (u8 *) & val);
> +	if (rc < 0)
> +		return -EIO;
> +
> +	/* Special case: the 32 bit regs are time values with 1/4s
> +	 * resolution, scale them up to milliseconds */
> +	if (sattr->nr == 4)
> +		return sprintf(buf, "%lli\n", ((u64) le32_to_cpu(val)) * 250);

%llu

> +
> +	/* Format the output string and return # of bytes */
> +	return sprintf(buf, "%li\n", (long)le32_to_cpu(val));
> +}
> +
> +static ssize_t ds1682_store(struct device *dev, struct device_attribute *attr,
> +			    const char *buf, size_t count)
> +{
> +	struct sensor_device_attribute_2 *sattr = to_sensor_dev_attr_2(attr);
> +	struct i2c_client *client = to_i2c_client(dev);
> +	char *endp;
> +	u64 val;
> +	__le32 val_le;
> +	int rc;
> +
> +	dev_dbg(dev, "ds1682_store() called on %s\n", attr->attr.name);
> +
> +	/* Decode input */
> +	val = simple_strtoull(buf, &endp, 0);
> +	if (buf == endp) {
> +		dev_dbg(dev, "input string not a number\n");
> +		return -EIO;

Rather -EINVAL, this isn't an I/O error.

> +	}
> +
> +	/* Special case: the 32 bit regs are time values with 1/4s
> +	 * resolution, scale input down to quarter-seconds */
> +	if (sattr->nr == 4)
> +		do_div(val, 250);
> +
> +	/* write out the value */
> +	val_le = cpu_to_le32(val);
> +	rc = i2c_smbus_write_i2c_block_data(client, sattr->index, sattr->nr,
> +					    (u8 *) & val);

Shouldn't this be (u8 *)&val_le?

> +	if (rc < 0) {
> +		dev_err(dev, "register write failed; reg=0x%x, size=%i\n",
> +			sattr->index, sattr->nr);
> +		return -EIO;
> +	}
> +
> +	return count;
> +}
> +
> +/*
> + * Simple register attributes
> + */
> +SENSOR_DEVICE_ATTR_2(config, S_IRUGO, ds1682_show, NULL, DS1682_REG_CONFIG, 1);

Bug! The last two arguments are swapped.

Also, I don't see the point of exporting this value to user-space, as
the format is proprietary.

> +SENSOR_DEVICE_ATTR_2(elapsed_time, S_IRUGO | S_IWUSR, ds1682_show, ds1682_store,
> +		     4, DS1682_REG_ELAPSED);
> +SENSOR_DEVICE_ATTR_2(alarm_time, S_IRUGO | S_IWUSR, ds1682_show, ds1682_store,
> +		     4, DS1682_REG_ALARM);
> +SENSOR_DEVICE_ATTR_2(event_count, S_IRUGO | S_IWUSR, ds1682_show, ds1682_store,
> +		     2, DS1682_REG_EVT_CNTR);
> +
> +static const struct attribute_group ds1682_group = {
> +	.attrs = (struct attribute *[]) {
> +		&sensor_dev_attr_config.dev_attr.attr,
> +		&sensor_dev_attr_elapsed_time.dev_attr.attr,
> +		&sensor_dev_attr_alarm_time.dev_attr.attr,
> +		&sensor_dev_attr_event_count.dev_attr.attr,
> +		NULL,
> +	},
> +};

I'm not sure if all compilers support this.

> +
> +/*
> + * User data attribute
> + */
> +static ssize_t ds1682_eeprom_read(struct kobject *kobj, char *buf, loff_t off,
> +				  size_t count)
> +{
> +	struct i2c_client *client = kobj_to_i2c_client(kobj);
> +	int rc;
> +
> +	dev_dbg(&client->dev, "ds1682_eeprom_read(p=%p, off=%lli, c=%zi)\n",
> +		buf, off, count);
> +
> +	if (off > DS1682_EEPROM_SIZE)

Should be ">=", otherwise you might end up doing a 0-length I2C block
read, which is bad.

> +		return 0;
> +
> +	if (off + count > DS1682_EEPROM_SIZE)
> +		count = DS1682_EEPROM_SIZE - off;
> +
> +	rc = i2c_smbus_read_i2c_block_data(client, DS1682_REG_EEPROM + off,
> +					   count, buf);
> +	if (rc < 0)
> +		return -EIO;
> +
> +	return count;
> +}
> +
> +static ssize_t ds1682_eeprom_write(struct kobject *kobj, char *buf, loff_t off,
> +				   size_t count)
> +{
> +	struct i2c_client *client = kobj_to_i2c_client(kobj);
> +
> +	dev_dbg(&client->dev, "ds1682_eeprom_write(p=%p, off=%lli, c=%zi)\n",
> +		buf, off, count);
> +
> +	if (off >= DS1682_EEPROM_SIZE)
> +		return -ENOSPC;
> +
> +	if (off + count > DS1682_EEPROM_SIZE)
> +		count = DS1682_EEPROM_SIZE - off;
> +
> +	/* Write out to the device */
> +	if (i2c_smbus_write_i2c_block_data(client, DS1682_REG_EEPROM + off,
> +					   count, buf) < 0)
> +		return -EIO;
> +
> +	return count;
> +}
> +
> +static struct bin_attribute ds1682_eeprom_attr = {
> +	.attr = {
> +		.name = "eeprom",
> +		.mode = S_IRUGO | S_IWUSR,
> +		.owner = THIS_MODULE,
> +	},
> +	.size = DS1682_EEPROM_SIZE,
> +	.read = ds1682_eeprom_read,
> +	.write = ds1682_eeprom_write,
> +};
> +
> +/*
> + * Called when a device is found at the ds1682 address
> + */

This comment is no longer true.

> +static int ds1682_probe(struct i2c_client *client)
> +{
> +	int err = 0;
> +
> +	if (client->addr != 0x6b) {
> +		dev_err(&client->dev, "%x is not a valid address\n",
> +			client->addr);
> +		return -ENODEV;
> +	}

Why check this? You should trust the person who wrote the device
definition in the platform code. The only reason why the older i2c chip
drivers did address checks is because that was one preliminary
device identification step. With the new model, you don't need to
identify the device, you already know what's there as per
architecture-level device declaration.

Not checking the address even has a benefit: if a compatible device
exists (today or in the future) with a different address, we don't need
to patch the driver to support it.

> +
> +	if (!i2c_check_functionality(client->adapter,
> +				     I2C_FUNC_SMBUS_READ_BYTE_DATA |
> +				     I2C_FUNC_SMBUS_WRITE_I2C_BLOCK)) {

This no longer reflects what the driver is using.

> +		dev_err(&client->dev, "i2c bus does not support the ds1682\n");
> +		goto exit;
> +	}
> +
> +	if (sysfs_create_group(&client->dev.kobj, &ds1682_group))

Missing "err = ".

> +		goto exit;
> +
> +	if (sysfs_create_bin_file(&client->dev.kobj, &ds1682_eeprom_attr))

Missing "err = ".

> +		goto exit_bin_attr;
> +
> +	return 0;
> +
> +      exit_bin_attr:
> +	sysfs_remove_group(&client->dev.kobj, &ds1682_group);
> +      exit:
> +	return err;
> +}
> +
> +static int ds1682_remove(struct i2c_client *client)
> +{
> +	sysfs_remove_bin_file(&client->dev.kobj, &ds1682_eeprom_attr);
> +	sysfs_remove_group(&client->dev.kobj, &ds1682_group);
> +
> +	return 0;
> +}
> +
> +static struct i2c_driver ds1682_driver = {
> +	.driver = {
> +		.name = "ds1682",
> +	},
> +	.probe = ds1682_probe,
> +	.remove = ds1682_remove,
> +};
> +
> +static int __init ds1682_init(void)
> +{
> +	return i2c_add_driver(&ds1682_driver);
> +}
> +
> +static void __exit ds1682_exit(void)
> +{
> +	i2c_del_driver(&ds1682_driver);
> +}
> +
> +MODULE_AUTHOR("Grant Likely <grant.likely@secretlab.ca>");
> +MODULE_DESCRIPTION("DS1682 Elapsed Time Indicator driver");
> +MODULE_LICENSE("GPL");
> +
> +module_init(ds1682_init);
> +module_exit(ds1682_exit);


-- 
Jean Delvare
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