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
battery)

This patch introduces a new sysfs entry to enable and disable this FET
form userspace.

Signed-off-by: Enric Balletbo i Serra <enric.balletbo@collabora.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>

1 files changed, 76 insertions, 0 deletions

diff --git a/drivers/rtc/rtc-bq32k.c b/drivers/rtc/rtc-bq32k.c
index 397742446007..2b223935001f 100644
--- a/drivers/rtc/rtc-bq32k.c
+++ b/drivers/rtc/rtc-bq32k.c
@@ -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,
+                   bq32k_sysfs_show_tricklecharge_bypass,
+                   bq32k_sysfs_store_tricklecharge_bypass);
+
+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) {
+                dev_err(&client->dev,
+                        "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)
+{
+        bq32k_sysfs_unregister(&client->dev);
+
+        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,
 };