Both the LTC2941 and LTC2943 measure battery capacity.
The LTC2943 is compatible with the LTC2941, it adds voltage and
temperature monitoring, and uses a slightly different conversion
formula for the charge counter.

To avoid confusion with e.g. the LTC2945, the driver is called
LTC2941 instead of LTC294X.

v2: Fix units of measurement: uV, uA and centidegrees.
v3: Correctly set configuration register. Allow negative values
    for the sense resistor.

Signed-off-by: Mike Looijmans <mike.looijm...@topic.nl>
---
 drivers/power/Kconfig                 |    7 +
 drivers/power/Makefile                |    1 +
 drivers/power/ltc2941-battery-gauge.c |  524 +++++++++++++++++++++++++++++++++
 3 files changed, 532 insertions(+)
 create mode 100644 drivers/power/ltc2941-battery-gauge.c

diff --git a/drivers/power/Kconfig b/drivers/power/Kconfig
index 73cfcdf..3333bf3 100644
--- a/drivers/power/Kconfig
+++ b/drivers/power/Kconfig
@@ -382,6 +382,13 @@ config CHARGER_TPS65090
         Say Y here to enable support for battery charging with TPS65090
         PMIC chips.
 
+config BATTERY_GAUGE_LTC2941
+       tristate "LTC2941/LTC2943 Battery Gauge Driver"
+       depends on I2C
+       help
+        Say Y here to include support for LTC2941 and LTC2943 Battery Gauge
+        IC.
+
 config AB8500_BM
        bool "AB8500 Battery Management Driver"
        depends on AB8500_CORE && AB8500_GPADC
diff --git a/drivers/power/Makefile b/drivers/power/Makefile
index dfa8942..4f8e6c0 100644
--- a/drivers/power/Makefile
+++ b/drivers/power/Makefile
@@ -36,6 +36,7 @@ obj-$(CONFIG_BATTERY_MAX17042)        += max17042_battery.o
 obj-$(CONFIG_BATTERY_Z2)       += z2_battery.o
 obj-$(CONFIG_BATTERY_S3C_ADC)  += s3c_adc_battery.o
 obj-$(CONFIG_BATTERY_TWL4030_MADC)     += twl4030_madc_battery.o
+obj-$(CONFIG_BATTERY_GAUGE_LTC2941)    += ltc2941-battery-gauge.o
 obj-$(CONFIG_CHARGER_88PM860X) += 88pm860x_charger.o
 obj-$(CONFIG_CHARGER_PCF50633) += pcf50633-charger.o
 obj-$(CONFIG_BATTERY_JZ4740)   += jz4740-battery.o
diff --git a/drivers/power/ltc2941-battery-gauge.c 
b/drivers/power/ltc2941-battery-gauge.c
new file mode 100644
index 0000000..f0c387d
--- /dev/null
+++ b/drivers/power/ltc2941-battery-gauge.c
@@ -0,0 +1,524 @@
+/*
+ * I2C client/driver for the Linear Technology LTC2941 and LTC2943
+ * Battery Gas Gauge IC
+ *
+ * Copyright (C) 2014 Topic Embedded Systems
+ *
+ * Author: Auryn Verwegen
+ * Author: Mike Looijmans
+ */
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/types.h>
+#include <linux/errno.h>
+#include <linux/swab.h>
+#include <linux/i2c.h>
+#include <linux/delay.h>
+#include <linux/idr.h>
+#include <linux/power_supply.h>
+#include <linux/slab.h>
+
+#define I16_MSB(x)                     ((x >> 8) & 0xFF)
+#define I16_LSB(x)                     (x & 0xFF)
+
+#define LTC294X_WORK_DELAY             10      /* Update delay in seconds */
+
+#define LTC294X_MAX_VALUE              0xFFFF
+#define LTC294X_MID_SUPPLY             0x7FFF
+
+#define LTC2941_MAX_PRESCALER_EXP      7
+#define LTC2943_MAX_PRESCALER_EXP      6
+
+enum ltc294x_reg {
+       LTC294X_REG_STATUS              = 0x00,
+       LTC294X_REG_CONTROL             = 0x01,
+       LTC294X_REG_ACC_CHARGE_MSB      = 0x02,
+       LTC294X_REG_ACC_CHARGE_LSB      = 0x03,
+       LTC294X_REG_THRESH_HIGH_MSB     = 0x04,
+       LTC294X_REG_THRESH_HIGH_LSB     = 0x05,
+       LTC294X_REG_THRESH_LOW_MSB      = 0x06,
+       LTC294X_REG_THRESH_LOW_LSB      = 0x07,
+       LTC294X_REG_VOLTAGE_MSB = 0x08,
+       LTC294X_REG_VOLTAGE_LSB = 0x09,
+       LTC294X_REG_CURRENT_MSB = 0x0E,
+       LTC294X_REG_CURRENT_LSB = 0x0F,
+       LTC294X_REG_TEMPERATURE_MSB     = 0x14,
+       LTC294X_REG_TEMPERATURE_LSB     = 0x15,
+} ;
+
+#define LTC2943_REG_CONTROL_MODE_MASK (BIT(7) | BIT(6))
+#define LTC2943_REG_CONTROL_MODE_SCAN BIT(7)
+#define LTC294X_REG_CONTROL_PRESCALER_MASK     (BIT(5) | BIT(4) | BIT(3))
+#define LTC294X_REG_CONTROL_SHUTDOWN_MASK      (BIT(0))
+#define LTC294X_REG_CONTROL_PRESCALER_SET(x)           ((x << 3) & 
LTC294X_REG_CONTROL_PRESCALER_MASK)
+#define LTC294X_REG_CONTROL_ALCC_CONFIG_DISABLED       0
+
+#define LTC2941_NUM_REGS       0x08
+#define LTC2943_NUM_REGS       0x18
+
+struct ltc294x_info {
+       struct i2c_client *client;      /* I2C Client pointer */
+       struct power_supply supply;     /* Supply pointer */
+       struct delayed_work work;       /* Work scheduler */
+       int num_regs; /* Number of registers (chip type) */
+       int     id;     /* Identifier of ltc294x chip */
+       int     charge; /* Last charge register content */
+       int     r_sense;        /* mOhm */
+       int Qlsb;       /* nAh */
+};
+
+static DEFINE_IDR(ltc294x_id);
+static DEFINE_MUTEX(ltc294x_lock);
+
+static inline int convert_bin_to_uAh(
+       const struct ltc294x_info *info, int Q)
+{
+       int uAh;
+       uAh = ((Q * (info->Qlsb / 10))) / 100;
+       return uAh;
+}
+
+static inline int convert_uAh_to_bin(
+       const struct ltc294x_info *info, int uAh)
+{
+       int Q;
+       Q = (uAh * 100) / (info->Qlsb/10);
+       return (Q < LTC294X_MAX_VALUE) ? Q : LTC294X_MAX_VALUE;
+}
+
+static int ltc294x_read_regs(struct i2c_client *client,
+    enum ltc294x_reg reg, u8 *buf, int num_regs)
+{
+       int ret;
+       struct i2c_msg msgs[2] = { };
+       u8 reg_start = reg;
+
+       msgs[0].addr    = client->addr;
+       msgs[0].len     = 1;
+       msgs[0].buf     = &reg_start;
+
+       msgs[1].addr    = client->addr;
+       msgs[1].len     = num_regs;
+       msgs[1].buf     = buf;
+       msgs[1].flags   = I2C_M_RD;
+
+       ret = i2c_transfer(client->adapter, &msgs[0], 2);
+       if (ret < 0) {
+               dev_err(&client->dev, "ltc2941 read_reg failed!\n");
+               return ret;
+       }
+
+       dev_dbg(&client->dev, "%s (%#x, %d) -> %#x\n",
+               __func__, reg, num_regs, *buf);
+
+       return 0;
+}
+
+static int ltc294x_write_regs(struct i2c_client *client,
+       enum ltc294x_reg reg, const u8* const buf, int num_regs)
+{
+       int ret;
+       u8 reg_start = reg;
+
+       ret = i2c_smbus_write_i2c_block_data(client, reg_start, num_regs, buf);
+       if (ret < 0) {
+               dev_err(&client->dev, "ltc2941 write_reg failed!\n");
+               return ret;
+       }
+
+       dev_dbg(&client->dev, "%s (%#x, %d) -> %#x\n",
+               __func__, reg, num_regs, *buf);
+
+       return 0;
+}
+
+static int ltc294x_reset(const struct ltc294x_info *info, int prescaler_exp)
+{
+       int ret;
+       u8 value;
+       u8 control;
+
+       /* Read status and control registers */
+       ret = ltc294x_read_regs(info->client, LTC294X_REG_CONTROL, &value, 1);
+       if(ret < 0) {
+               dev_err(&info->client->dev, "LTC2941: Could not read registers 
from device!\n");
+               goto error_exit;
+       }
+
+       control = LTC294X_REG_CONTROL_PRESCALER_SET(prescaler_exp) |
+                               LTC294X_REG_CONTROL_ALCC_CONFIG_DISABLED;
+       /* Put the 2943 into "monitor" mode, so it measures every 10 sec */
+       if (info->num_regs == LTC2943_NUM_REGS)
+               control |= LTC2943_REG_CONTROL_MODE_SCAN;
+
+       if (value != control) {
+               ret = ltc294x_write_regs(info->client, LTC294X_REG_CONTROL, 
&control, 1);
+               if(ret < 0){
+                       dev_err(&info->client->dev, "Could not write 
registers!\n");
+                       goto error_exit;
+               }
+       }
+
+       return 0;
+
+error_exit:
+       return ret;
+}
+
+static int ltc294x_read_charge_register(const struct ltc294x_info *info)
+{
+       int ret;
+       u8 datar[2];
+
+       ret = ltc294x_read_regs(info->client, LTC294X_REG_ACC_CHARGE_MSB, 
&datar[0], 2);
+       if (ret < 0)
+               return ret;
+       return (datar[0] << 8) + datar[1];
+}
+
+static int ltc294x_get_charge_now(const struct ltc294x_info *info, int *val)
+{
+       int value = ltc294x_read_charge_register(info);
+       if (value < 0)
+               return value;
+       /* When r_sense < 0, this counts up when the battery discharges */
+       if (info->Qlsb < 0)
+               value -= 0xFFFF;
+       *val = convert_bin_to_uAh(info, value);
+       return 0;
+}
+
+static int ltc294x_set_charge_now(const struct ltc294x_info *info, int val)
+{
+       int ret;
+       u8 dataw[2];
+       u8 ctrl_reg;
+       s32 value;
+
+       value = convert_uAh_to_bin(info, val);
+       if (info->Qlsb < 0) /* Direction depends on how sense+/- were connected 
*/
+               value += 0xFFFF;
+       if ((value < 0) || (value > 0xFFFF)) /* input validation */
+               return -EINVAL;
+
+       /* Read control register */
+       ret = ltc294x_read_regs(info->client, LTC294X_REG_CONTROL, &ctrl_reg, 
1);
+       if(ret < 0)
+               return ret;
+       /* Disable analog section */
+       ctrl_reg |= LTC294X_REG_CONTROL_SHUTDOWN_MASK;
+       ret = ltc294x_write_regs(info->client, LTC294X_REG_CONTROL, &ctrl_reg, 
1);
+       if(ret < 0)
+               return ret;
+       /* Set new charge value */
+       dataw[0] = I16_MSB(value);
+       dataw[1] = I16_LSB(value);
+       ret = ltc294x_write_regs(info->client, LTC294X_REG_ACC_CHARGE_MSB, 
&dataw[0], 2);
+       if(ret < 0)
+               goto error_exit;
+       /* Enable analog section */
+error_exit:
+       ctrl_reg &= ~LTC294X_REG_CONTROL_SHUTDOWN_MASK;
+       ret = ltc294x_write_regs(info->client, LTC294X_REG_CONTROL, &ctrl_reg, 
1);
+
+       return ret < 0 ? ret : 0;
+}
+
+static int ltc294x_get_charge_counter(const struct ltc294x_info *info, int 
*val)
+{
+       int value = ltc294x_read_charge_register(info);
+       if (value < 0)
+               return value;
+       value -= LTC294X_MID_SUPPLY;
+       *val = convert_bin_to_uAh(info, value);
+       return 0;
+}
+
+static int ltc294x_get_voltage(const struct ltc294x_info *info, int *val)
+{
+       int ret;
+       u8 datar[2];
+       u32 value;
+
+       ret = ltc294x_read_regs(info->client, LTC294X_REG_VOLTAGE_MSB, 
&datar[0], 2);
+       value = (datar[0] << 8) | datar[1];
+       *val = ((value * 23600) / 0xFFFF) * 1000; /* in uV */
+       return ret;
+}
+
+static int ltc294x_get_current(const struct ltc294x_info *info, int *val)
+{
+       int ret;
+       u8 datar[2];
+       s32 value;
+
+       ret = ltc294x_read_regs(info->client, LTC294X_REG_CURRENT_MSB, 
&datar[0], 2);
+       value = (datar[0] << 8) | datar[1];
+       value -= 0x7FFF;
+       /* Value is in range -32k..+32k, r_sense is usually 10..50 mOhm,
+        * the formula below keeps everything in s32 range while preserving
+        * enough digits */
+       *val = 1000 * ((60000 * value) / (info->r_sense * 0x7FFF)); /* in uA */
+       return ret;
+}
+
+static int ltc294x_get_temperature(const struct ltc294x_info *info, int *val)
+{
+       int ret;
+       u8 datar[2];
+       u32 value;
+
+       ret = ltc294x_read_regs(info->client, LTC294X_REG_TEMPERATURE_MSB, 
&datar[0], 2);
+       value = (datar[0] << 8) | datar[1];
+       /* Full-scale is 510 Kelvin, convert to centidegrees  */
+       *val = (((51000 * value) / 0xFFFF) - 27215);
+       return ret;
+}
+
+static int ltc294x_get_property(struct power_supply *psy,
+                               enum power_supply_property prop,
+                               union power_supply_propval *val)
+{
+       struct ltc294x_info *info = container_of(psy, struct ltc294x_info, 
supply);
+
+       switch (prop) {
+               case POWER_SUPPLY_PROP_CHARGE_NOW:
+                       return ltc294x_get_charge_now(info, &val->intval);
+               case POWER_SUPPLY_PROP_CHARGE_COUNTER:
+                       return ltc294x_get_charge_counter(info, &val->intval);
+               case POWER_SUPPLY_PROP_VOLTAGE_NOW:
+                       return ltc294x_get_voltage(info, &val->intval);
+               case POWER_SUPPLY_PROP_CURRENT_NOW:
+                       return ltc294x_get_current(info, &val->intval);
+               case POWER_SUPPLY_PROP_TEMP:
+                       return ltc294x_get_temperature(info, &val->intval);
+               default:
+                       return -EINVAL;
+       }
+}
+
+static int ltc294x_set_property(struct power_supply *psy,
+       enum power_supply_property psp,
+       const union power_supply_propval *val)
+{
+       struct ltc294x_info *info =
+               container_of(psy, struct ltc294x_info, supply);
+
+       switch (psp) {
+               case POWER_SUPPLY_PROP_CHARGE_NOW:
+                       return ltc294x_set_charge_now(info, val->intval);
+               default:
+                       return -EPERM;
+       }
+}
+
+static int ltc294x_property_is_writeable(
+       struct power_supply *psy, enum power_supply_property psp)
+{
+       switch (psp)
+       {
+               case POWER_SUPPLY_PROP_CHARGE_NOW:
+                       return 1;
+               default:
+                       return 0;
+       }
+}
+
+static void ltc294x_update(struct ltc294x_info *info)
+{
+       int charge = ltc294x_read_charge_register(info);
+       if (charge != info->charge) {
+               info->charge = charge;
+               power_supply_changed(&info->supply);
+       }
+}
+
+static void ltc294x_work(struct work_struct *work)
+{
+       struct ltc294x_info *info;
+
+       info = container_of(work, struct ltc294x_info, work.work);
+       ltc294x_update(info);
+       schedule_delayed_work(&info->work, LTC294X_WORK_DELAY * HZ);
+}
+
+static enum power_supply_property ltc294x_properties[] = {
+       POWER_SUPPLY_PROP_CHARGE_COUNTER,
+       POWER_SUPPLY_PROP_CHARGE_NOW,
+       POWER_SUPPLY_PROP_VOLTAGE_NOW,
+       POWER_SUPPLY_PROP_CURRENT_NOW,
+       POWER_SUPPLY_PROP_TEMP,
+};
+
+static int ltc294x_i2c_remove(struct i2c_client *client)
+{
+       struct ltc294x_info *info = i2c_get_clientdata(client);
+
+       cancel_delayed_work(&info->work);
+       power_supply_unregister(&info->supply);
+       kfree(info->supply.name);
+       mutex_lock(&ltc294x_lock);
+       idr_remove(&ltc294x_id, info->id);
+       mutex_unlock(&ltc294x_lock);
+       return 0;
+}
+
+static int ltc294x_i2c_probe(struct i2c_client *client, const struct 
i2c_device_id *id)
+{
+       struct ltc294x_info *info;
+       int ret;
+       int num;
+       u32 prescaler_exp;
+       s32 r_sense;
+       struct device_node *np;
+
+       mutex_lock(&ltc294x_lock);
+       ret = idr_alloc(&ltc294x_id, client, 0, 0, GFP_KERNEL);
+       mutex_unlock(&ltc294x_lock);
+       if(ret < 0)
+               goto fail_id;
+
+       num = ret;
+
+       info = devm_kzalloc(&client->dev, sizeof(*info), GFP_KERNEL);
+       if(info == NULL) {
+               dev_err(&client->dev, "Could not allocate memory for device 
structure!\n");
+               ret = -ENOMEM;
+               goto fail_info;
+       }
+
+       i2c_set_clientdata(client, info);
+
+       info->num_regs = id->driver_data;
+       info->supply.name = kasprintf(GFP_KERNEL, "%s-%d", client->name, num);
+       if(!info->supply.name) {
+               dev_err(&client->dev, "Could not allocate memory for device 
name!\n");
+               ret = -ENOMEM;
+               goto fail_name;
+       }
+
+       np = of_node_get(client->dev.of_node);
+
+       /* r_sense can be negative, when sense+ is connected to the battery
+        * instead of the sense-. This results in reversed measurements. */
+       ret = of_property_read_u32(np, "resistor-sense", &r_sense);
+       if(ret < 0) {
+               dev_err(&client->dev, "Could not find resistor-sense in 
devicetree!\n");
+               goto fail_name;
+       }
+       info->r_sense = r_sense;
+
+       ret = of_property_read_u32(np, "prescaler-exponent", &prescaler_exp);
+       if(ret < 0) {
+               dev_err(&client->dev, "PrescalerExponent not in devicetree, 
assume max.\n");
+               prescaler_exp = LTC2941_MAX_PRESCALER_EXP;
+       }
+
+       if (info->num_regs == LTC2943_NUM_REGS) {
+               if (prescaler_exp > LTC2943_MAX_PRESCALER_EXP)
+                       prescaler_exp = LTC2943_MAX_PRESCALER_EXP;
+               info->Qlsb = ((340 * 50000) / r_sense) / (4096 / (1 << 
(2*prescaler_exp)));
+       } else {
+               if (prescaler_exp > LTC2941_MAX_PRESCALER_EXP)
+                       prescaler_exp = LTC2941_MAX_PRESCALER_EXP;
+               info->Qlsb = ((58 * 50000) / r_sense) / (128 / (1 << 
prescaler_exp));
+       }
+
+       info->client = client;
+       info->id = num;
+       info->supply.type                       = POWER_SUPPLY_TYPE_BATTERY;
+       info->supply.properties                 = ltc294x_properties;
+       if (info->num_regs >= LTC294X_REG_TEMPERATURE_LSB)
+               info->supply.num_properties     = 
ARRAY_SIZE(ltc294x_properties);
+       else if (info->num_regs >= LTC294X_REG_CURRENT_LSB)
+               info->supply.num_properties     = 
ARRAY_SIZE(ltc294x_properties) - 1;
+       else if (info->num_regs >= LTC294X_REG_VOLTAGE_LSB)
+               info->supply.num_properties     = 
ARRAY_SIZE(ltc294x_properties) - 2;
+       else
+               info->supply.num_properties     = 
ARRAY_SIZE(ltc294x_properties) - 3;
+       info->supply.get_property               = ltc294x_get_property;
+       info->supply.set_property               = ltc294x_set_property;
+       info->supply.property_is_writeable      = ltc294x_property_is_writeable;
+       info->supply.external_power_changed     = NULL;
+
+       INIT_DELAYED_WORK(&info->work, ltc294x_work);
+
+       ret = ltc294x_reset(info, prescaler_exp);
+       if (ret < 0) {
+               dev_err(&client->dev, "Communication with chip failed!\n");
+               goto fail_comm;
+       }
+
+       ret = power_supply_register(&client->dev, &info->supply);
+       if (ret) {
+               dev_err(&client->dev, "failed to register ltc2941\n");
+               goto fail_register;
+       } else {
+               schedule_delayed_work(&info->work, LTC294X_WORK_DELAY * HZ);
+       }
+
+       return 0;
+
+fail_register:
+       kfree(info->supply.name);
+fail_comm:
+fail_name:
+fail_info:
+       mutex_lock(&ltc294x_lock);
+       idr_remove(&ltc294x_id, num);
+       mutex_unlock(&ltc294x_lock);
+fail_id:
+       return ret;
+}
+
+#ifdef CONFIG_PM_SLEEP
+
+static int ltc294x_suspend(struct device *dev)
+{
+       struct i2c_client *client = to_i2c_client(dev);
+       struct ltc294x_info *info = i2c_get_clientdata(client);
+
+       cancel_delayed_work(&info->work);
+       return 0;
+}
+
+static int ltc294x_resume(struct device *dev)
+{
+       struct i2c_client *client = to_i2c_client(dev);
+       struct ltc294x_info *info = i2c_get_clientdata(client);
+
+       schedule_delayed_work(&info->work, LTC294X_WORK_DELAY * HZ);
+       return 0;
+}
+
+static SIMPLE_DEV_PM_OPS(ltc294x_pm_ops, ltc294x_suspend, ltc294x_resume);
+#define LTC294X_PM_OPS (&ltc294x_pm_ops)
+
+#else
+#define LTC294X_PM_OPS NULL
+#endif /* CONFIG_PM_SLEEP */
+
+
+static const struct i2c_device_id ltc294x_i2c_id[] = {
+       {"ltc2941", LTC2941_NUM_REGS},
+       {"ltc2943", LTC2943_NUM_REGS},
+       { },
+};
+MODULE_DEVICE_TABLE(i2c, ltc294x_i2c_id);
+
+static struct i2c_driver ltc294x_driver = {
+       .driver         = {
+               .name   = "LTC2941",
+               .owner  = THIS_MODULE,
+               .pm     = LTC294X_PM_OPS,
+       },
+       .probe          = ltc294x_i2c_probe,
+       .remove         = ltc294x_i2c_remove,
+       .id_table       = ltc294x_i2c_id,
+};
+module_i2c_driver(ltc294x_driver);
+
+MODULE_AUTHOR("Auryn Verwegen, Topic Embedded Systems");
+MODULE_AUTHOR("Mike Looijmans, Topic Embedded Products");
+MODULE_DESCRIPTION("LTC2941/LTC2943 Battery Gas Gauge IC driver");
+MODULE_LICENSE("GPL");
-- 
1.7.9.5

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