Commit 4c466872 authored by Enric Balletbo i Serra's avatar Enric Balletbo i Serra Committed by Alexandre Belloni

rtc: bq32000: add support to enable disable the trickle charge FET bypass

The bq32000 includes a trickle charge circuit to maintain the charge of the
backup supply when a super capacitor is used.

You can enable the charging circuit by setting 'trickle-resistor-ohms',
additionally you can set TCFE to 1 to bypass the internal diode and boost
the charge voltage of the backup supply. You might want to enable/disable
the TCFE switch from userspace (e.g when device is only connected to a

This patch introduces a new sysfs entry to enable and disable this FET
form userspace.
Signed-off-by: default avatarEnric Balletbo i Serra <[email protected]>
Signed-off-by: default avatarAlexandre Belloni <[email protected]>
parent 5dff3a31
What: /sys/bus/i2c/devices/.../trickle_charge_bypass
Date: Jan 2017
KernelVersion: 4.11
Contact: Enric Balletbo i Serra <[email protected]>
Description: Attribute for enable/disable the trickle charge bypass
The trickle_charge_bypass attribute allows the userspace to
enable/disable the Trickle charge FET bypass.
......@@ -34,6 +34,7 @@
#define BQ32K_CALIBRATION 0x07 /* CAL_CFG1, calibration and control */
#define BQ32K_TCH2 0x08 /* Trickle charge enable */
#define BQ32K_CFG2 0x09 /* Trickle charger control */
#define BQ32K_TCFE BIT(6) /* Trickle charge FET bypass */
struct bq32k_regs {
uint8_t seconds;
......@@ -188,6 +189,65 @@ static int trickle_charger_of_init(struct device *dev, struct device_node *node)
return 0;
static ssize_t bq32k_sysfs_show_tricklecharge_bypass(struct device *dev,
struct device_attribute *attr,
char *buf)
int reg, error;
error = bq32k_read(dev, &reg, BQ32K_CFG2, 1);
if (error)
return error;
return sprintf(buf, "%d\n", (reg & BQ32K_TCFE) ? 1 : 0);
static ssize_t bq32k_sysfs_store_tricklecharge_bypass(struct device *dev,
struct device_attribute *attr,
const char *buf, size_t count)
int reg, enable, error;
if (kstrtoint(buf, 0, &enable))
return -EINVAL;
error = bq32k_read(dev, &reg, BQ32K_CFG2, 1);
if (error)
return error;
if (enable) {
reg |= BQ32K_TCFE;
error = bq32k_write(dev, &reg, BQ32K_CFG2, 1);
if (error)
return error;
dev_info(dev, "Enabled trickle charge FET bypass.\n");
} else {
reg &= ~BQ32K_TCFE;
error = bq32k_write(dev, &reg, BQ32K_CFG2, 1);
if (error)
return error;
dev_info(dev, "Disabled trickle charge FET bypass.\n");
return count;
static DEVICE_ATTR(trickle_charge_bypass, 0644,
static int bq32k_sysfs_register(struct device *dev)
return device_create_file(dev, &dev_attr_trickle_charge_bypass);
static void bq32k_sysfs_unregister(struct device *dev)
device_remove_file(dev, &dev_attr_trickle_charge_bypass);
static int bq32k_probe(struct i2c_client *client,
const struct i2c_device_id *id)
......@@ -224,11 +284,26 @@ static int bq32k_probe(struct i2c_client *client,
if (IS_ERR(rtc))
return PTR_ERR(rtc);
error = bq32k_sysfs_register(&client->dev);
if (error) {
"Unable to create sysfs entries for rtc bq32000\n");
return error;
i2c_set_clientdata(client, rtc);
return 0;
static int bq32k_remove(struct i2c_client *client)
return 0;
static const struct i2c_device_id bq32k_id[] = {
{ "bq32000", 0 },
{ }
......@@ -240,6 +315,7 @@ static struct i2c_driver bq32k_driver = {
.name = "bq32k",
.probe = bq32k_probe,
.remove = bq32k_remove,
.id_table = bq32k_id,
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