m41txx chips can hold a calibration value to get really near to real
tick value.
Add calibration property(ranging between (-31) and 31), so on every probe
calibration value will be written to rtc.
This is because ic could loose supply due to low battery.
Signed-off-by: Giulio Benetti <giulio.benetti@xxxxxxxxxxxxxxxx>
---
.../devicetree/bindings/rtc/rtc-ds1307.txt | 2 ++
drivers/rtc/rtc-ds1307.c | 33 +++++++++++++++++++
2 files changed, 35 insertions(+)
diff --git a/Documentation/devicetree/bindings/rtc/rtc-ds1307.txt b/Documentation/devicetree/bindings/rtc/rtc-ds1307.txt
index ce6469c1a516..d3d70a5495c5 100644
--- a/Documentation/devicetree/bindings/rtc/rtc-ds1307.txt
+++ b/Documentation/devicetree/bindings/rtc/rtc-ds1307.txt
@@ -34,6 +34,8 @@ Optional properties:
- trickle-diode-disable : ds1339, ds1340 and ds 1388 only
Do not use internal trickle charger diode
Should be given if internal trickle charger diode should be disabled
+- calibration: m41t0, m41t00, m41t11 only
+ Set calibration value to correct external bias, ranging between (-31) and 31.
Example:
rtc1: ds1339@68 {
diff --git a/drivers/rtc/rtc-ds1307.c b/drivers/rtc/rtc-ds1307.c
index 0ab0c166da83..9cda52589c0f 100644
--- a/drivers/rtc/rtc-ds1307.c
+++ b/drivers/rtc/rtc-ds1307.c
@@ -114,6 +114,12 @@ enum ds_type {
# define RX8025_BIT_VDET 0x40
# define RX8025_BIT_XST 0x20
+#define M41TXX_REG_CONTROL 0x07
+# define M41TXX_BIT_OUT 0x80
+# define M41TXX_BIT_FT 0x40
+# define M41TXX_BIT_CALIB_SIGN 0x20
+# define M41TXX_M_CALIBRATION 0x1f
+
struct ds1307 {
enum ds_type type;
unsigned long flags;
@@ -1397,6 +1403,7 @@ static int ds1307_probe(struct i2c_client *client,
unsigned char regs[8];
struct ds1307_platform_data *pdata = dev_get_platdata(&client->dev);
u8 trickle_charger_setup = 0;
+ s32 calib;
ds1307 = devm_kzalloc(&client->dev, sizeof(struct ds1307), GFP_KERNEL);
if (!ds1307)
@@ -1460,6 +1467,32 @@ static int ds1307_probe(struct i2c_client *client,
if (chip->alarm && of_property_read_bool(client->dev.of_node,
"wakeup-source"))
ds1307_can_wakeup_device = true;
+
+ /* retrieve calibration value if provided */
+ if (!of_property_read_s32(client->dev.of_node, "calibration",
+ &calib)) {
+ switch (ds1307->type) {
+ case m41t0:
+ case m41t00:
+ case m41t11:
+ {
+ /*
+ * Set calibration value every power-on since rtc
+ * could have shut off(low battery)
+ */
+ u8 out_byte = abs(calib) & M41TXX_M_CALIBRATION;
+
+ if (calib >= 0)
+ out_byte |= M41TXX_BIT_CALIB_SIGN;
+
+ regmap_write(ds1307->regmap, M41TXX_REG_CONTROL,
+ out_byte);
+ }
+ break;
+ default:
+ break;
+ }
+ }
#endif
switch (ds1307->type) {
--
2.17.0
