Message-ID: <20090617110908.17b47a18@hyperion.delvare>
Date:	Wed, 17 Jun 2009 11:09:08 +0200
From:	Jean Delvare <khali@...ux-fr.org>
To:	Ryan Mallon <ryan@...ewatersys.com>
Cc:	linux kernel <linux-kernel@...r.kernel.org>,
	linux-i2c@...r.kernel.org, Anton Vorontsov <cbou@...l.ru>,
	David Woodhouse <dwmw2@...radead.org>
Subject: Re: [PATCH] ds2782 battery gas gauge driver

Hi Ryan,

On Tue, 16 Jun 2009 16:17:35 +1200, Ryan Mallon wrote:
> Add support for the the ds2782 standalone I2C gas-gauge.
> 
> Signed-off-by: Ryan Mallon <ryan@...ewatersys.com>

I suggest you send this patch to the maintainers of the power supply
subsystem for review: Anton Vorontsov and David Woodhouse (Cc'd.)

Also see my random comments inline:

> 
> ---
> 
> diff --git a/drivers/power/Kconfig b/drivers/power/Kconfig
> index 33da112..b9c818f 100644
> --- a/drivers/power/Kconfig
> +++ b/drivers/power/Kconfig
> @@ -43,6 +43,13 @@ config BATTERY_DS2760
>  	help
>  	  Say Y here to enable support for batteries with ds2760 chip.
>  
> +config BATTERY_DS2782
> +	tristate "DS2782 standalone gas-gauge"
> +	depends on I2C
> +	help
> +	  Say Y here to enable support for the DS2782 standalone battery
> +	  gas-gauge.
> +
>  config BATTERY_PMU
>  	tristate "Apple PMU battery"
>  	depends on PPC32 && ADB_PMU
> diff --git a/drivers/power/Makefile b/drivers/power/Makefile
> index 2fcf41d..ad1ac61 100644
> --- a/drivers/power/Makefile
> +++ b/drivers/power/Makefile
> @@ -19,6 +19,7 @@ obj-$(CONFIG_APM_POWER)		+= apm_power.o
>  obj-$(CONFIG_WM8350_POWER)	+= wm8350_power.o
>  
>  obj-$(CONFIG_BATTERY_DS2760)	+= ds2760_battery.o
> +obj-$(CONFIG_BATTERY_DS2782)	+= ds2782_battery.o
>  obj-$(CONFIG_BATTERY_PMU)	+= pmu_battery.o
>  obj-$(CONFIG_BATTERY_OLPC)	+= olpc_battery.o
>  obj-$(CONFIG_BATTERY_TOSA)	+= tosa_battery.o
> diff --git a/drivers/power/ds2782_battery.c b/drivers/power/ds2782_battery.c
> new file mode 100644
> index 0000000..8697891
> --- /dev/null
> +++ b/drivers/power/ds2782_battery.c
> @@ -0,0 +1,269 @@
> +/*
> + * drivers/power/ds2782_battery.c
> + *
> + * I2C client/driver for the Maxim/Dallas DS2782 Stand-Alone Fuel Gauge IC
> + *
> + * Copyright (C) 2009 Bluewater Systems Ltd
> + * Author: Ryan Mallon <ryan@...ewatersys.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/kernel.h>
> +#include <linux/module.h>
> +#include <linux/i2c.h>
> +#include <linux/idr.h>
> +#include <linux/power_supply.h>
> +
> +#define DS2782_REG_RARC		0x06	/* Remaining active relative capacity */
> +
> +#define DS2782_REG_VOLT_MSB	0x0c
> +#define DS2782_REG_TEMP_MSB	0x0a
> +#define DS2782_REG_CURRENT_MSB	0x0e
> +
> +/* EEPROM Block */
> +#define DS2782_REG_RSNSP	0x69	/* Sense resistor value */
> +
> +/* Current unit measurement in uA for a 1 milli-ohm sense resistor */
> +#define DS2782_CURRENT_UNITS	1563
> +
> +#define to_ds2782_info(x) container_of(x, struct ds2782_info, battery)
> +
> +struct ds2782_info {
> +	struct i2c_client	*client;
> +	struct power_supply	battery;
> +	int			id;
> +};
> +
> +static DEFINE_IDR(battery_id);
> +static DEFINE_MUTEX(battery_lock);
> +
> +static inline u8 ds2782_read_reg(struct ds2782_info *info, int reg)
> +{
> +	return i2c_smbus_read_byte_data(info->client, reg);

This lacks error checking.

> +}
> +
> +static inline u16 ds2782_read_reg16(struct ds2782_info *info, int reg_msb)
> +{
> +	u8 msb, lsb;
> +
> +	msb = ds2782_read_reg(info, reg_msb);
> +	lsb = ds2782_read_reg(info, reg_msb + 1);
> +
> +	return (msb << 8) | lsb;
> +}

You should be able to use i2c_smbus_read_word_data() for this (possibly
together with swab16 to correct byte ordering). This is recommended in
the datasheet to prevent a data update in the middle of a read.

> +
> +static int ds2782_get_temp(struct ds2782_info *info)
> +{
> +	u16 raw;
> +	s16 temp;
> +
> +	/* Temperature is measured in units of 0.125 degrees celcius */
> +	raw = ds2782_read_reg16(info, DS2782_REG_TEMP_MSB);
> +	temp = (raw >> 5) & 0x7ff;
> +	if (raw & (1 << 15))
> +		temp |= 0xf800;
> +	return (temp * 125) / 100;
> +}

I don't know if the power supply class has a standard to reporting
temperature values, but the hwmon class does, and it says that
temperatures should be reported in millidegrees C. That's not what you
do here AFAICS. It might be convenient to register a hwmon class device
and export the temperature there, so that libsensors picks it.

I also believe your math is a little more complex than it has to be. If
you just read the register value into an s16 and divide by 32, the sign
will be preserved.

> +
> +static int ds2782_get_current(struct ds2782_info *info)
> +{
> +	s16 current_uA;
> +	int sense_res;
> +
> +	/*
> +	 * The units of measurement for current are dependent on the value of
> +	 * the sense resistor.
> +	 */
> +	sense_res = 1000 / ds2782_read_reg(info, DS2782_REG_RSNSP);

If ds2782_read_reg() returns 0, you crash your kernel. No good.

> +	dev_dbg(&info->client->dev, "sense resistor = %d milli-ohms\n",
> +		sense_res);
> +	current_uA = ds2782_read_reg16(info, DS2782_REG_CURRENT_MSB);
> +	return current_uA * (DS2782_CURRENT_UNITS / sense_res);
> +}
> +
> +static int ds2782_get_voltage(struct ds2782_info *info)
> +{
> +	u16 raw;
> +	s16 voltage_uA;
> +
> +	/* Voltage is measured in units of 4.88mV */
> +	raw = ds2782_read_reg16(info, DS2782_REG_VOLT_MSB);
> +	voltage_uA = (raw >> 5) & 0x7ff;
> +	if (raw & (1 << 15))
> +		voltage_uA |= 0xf800;
> +	return voltage_uA * 4880;
> +}

This too might be good to export to the hwmon class.

> +
> +static int ds2782_get_status(struct ds2782_info *info)
> +{
> +	int current_uA, capacity;
> +
> +	current_uA = ds2782_get_current(info);
> +	capacity = ds2782_read_reg(info, DS2782_REG_RARC);
> +
> +	if (capacity == 100)
> +		return POWER_SUPPLY_STATUS_FULL;
> +	else if (current_uA == 0)
> +		return POWER_SUPPLY_STATUS_NOT_CHARGING;
> +	else if (current_uA < 0)
> +		return POWER_SUPPLY_STATUS_DISCHARGING;
> +	else
> +		return POWER_SUPPLY_STATUS_CHARGING;
> +}
> +
> +static int ds2782_battery_get_property(struct power_supply *psy,
> +				       enum power_supply_property prop,
> +				       union power_supply_propval *val)
> +{
> +	struct ds2782_info *info = to_ds2782_info(psy);
> +
> +	switch (prop) {
> +	case POWER_SUPPLY_PROP_STATUS:
> +		val->intval = ds2782_get_status(info);
> +		break;
> +
> +	case POWER_SUPPLY_PROP_CAPACITY:
> +		val->intval = ds2782_read_reg(info, DS2782_REG_RARC);
> +		break;
> +
> +	case POWER_SUPPLY_PROP_VOLTAGE_NOW:
> +		val->intval = ds2782_get_voltage(info);
> +		break;
> +
> +	case POWER_SUPPLY_PROP_CURRENT_NOW:
> +		val->intval = ds2782_get_current(info);
> +		break;
> +
> +	case POWER_SUPPLY_PROP_TEMP:
> +		val->intval = ds2782_get_temp(info);
> +		break;
> +
> +	default:
> +		return -EINVAL;
> +	}
> +
> +	return 0;
> +}
> +
> +static enum power_supply_property ds2782_battery_props[] = {
> +	POWER_SUPPLY_PROP_STATUS,
> +	POWER_SUPPLY_PROP_CAPACITY,
> +	POWER_SUPPLY_PROP_VOLTAGE_NOW,
> +	POWER_SUPPLY_PROP_CURRENT_NOW,
> +	POWER_SUPPLY_PROP_TEMP,
> +};
> +
> +static void ds2782_power_supply_init(struct power_supply *battery)
> +{
> +	battery->type			= POWER_SUPPLY_TYPE_BATTERY;
> +	battery->properties		= ds2782_battery_props;
> +	battery->num_properties		= ARRAY_SIZE(ds2782_battery_props);
> +	battery->get_property		= ds2782_battery_get_property;
> +	battery->external_power_changed	= NULL;

Initializing fields of a zalloc'd structure to NULL is a no-op.

> +}
> +
> +static int ds2782_battery_remove(struct i2c_client *client)
> +{
> +	struct ds2782_info *info = i2c_get_clientdata(client);
> +
> +	power_supply_unregister(&info->battery);
> +	kfree(info->battery.name);
> +
> +	mutex_lock(&battery_lock);
> +	idr_remove(&battery_id, info->id);
> +	mutex_unlock(&battery_lock);
> +

Please insert:
	i2c_set_clientdata(client, info);
to not leave a dangling pointer behind.

> +	kfree(info);
> +	return 0;
> +}
> +
> +static int ds2782_battery_probe(struct i2c_client *client,
> +				const struct i2c_device_id *id)
> +{
> +	struct ds2782_info *info;
> +	int ret, num;
> +
> +	/* Get an ID for this battery */
> +	ret = idr_pre_get(&battery_id, GFP_KERNEL);
> +	if (ret == 0) {
> +		ret = -ENOMEM;
> +		goto fail_id;
> +	}
> +
> +	mutex_lock(&battery_lock);
> +	ret = idr_get_new(&battery_id, client, &num);
> +	mutex_unlock(&battery_lock);
> +	if (ret < 0)
> +		return ret;

For consistency this should be a goto.

> +
> +	info = kzalloc(sizeof(struct ds2782_info), GFP_KERNEL);
> +	if (!info) {
> +		ret = -ENOMEM;
> +		goto fail_info;
> +	}
> +
> +	info->battery.name = kasprintf(GFP_KERNEL, "ds2782-%d", num);
> +	if (!info->battery.name) {
> +		ret = -ENOMEM;
> +		goto fail_name;
> +	}
> +
> +	i2c_set_clientdata(client, info);
> +	info->client = client;
> +	ds2782_power_supply_init(&info->battery);
> +
> +	ret = power_supply_register(&client->dev, &info->battery);
> +	if (ret) {
> +		dev_err(&client->dev, "failed to register battery\n");
> +		goto fail_register;
> +	}
> +
> +	return 0;
> +
> +fail_register:
> +	kfree(info->battery.name);
> +fail_name:

Please insert:
	i2c_set_clientdata(client, info);
to not leave a dangling pointer behind.

> +	kfree(info);
> +fail_info:
> +	mutex_lock(&battery_lock);
> +	idr_remove(&battery_id, num);
> +	mutex_unlock(&battery_lock);
> +fail_id:
> +	return ret;
> +}
> +
> +static const struct i2c_device_id ds2782_id[] = {
> +	{"ds2782", 0},
> +	{},
> +};
> +
> +static struct i2c_driver ds2782_battery_driver = {
> +	.driver 	= {
> +		.name	= "ds2782-battery",
> +	},
> +	.probe		= ds2782_battery_probe,
> +	.remove		= ds2782_battery_remove,
> +	.id_table	= ds2782_id,
> +};
> +
> +static int __init ds2782_init(void)
> +{
> +	return i2c_add_driver(&ds2782_battery_driver);
> +}
> +
> +static void __exit ds2782_exit(void)
> +{
> +	i2c_del_driver(&ds2782_battery_driver);
> +}
> +
> +module_init(ds2782_init);
> +module_exit(ds2782_exit);
> +
> +MODULE_AUTHOR("Ryan Mallon <ryan@...ewatersys.com>");
> +MODULE_DESCRIPTION("Maxim/Dallas DS2782 Stand-Alone Fuel Gauage IC driver");
> +MODULE_LICENSE("GPL");
> +

Useless blank line ;)

-- 
Jean Delvare
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