[PATCH 4.14 53/53] rtc: pcf8523: dont return invalid date when battery is low

[Greg Kroah-Hartman]

From: Baruch Siach <bar...@tkos.co.il>

commit ecb4a353d3afd45b9bb30c85d03ee113a0589079 upstream.

The RTC_VL_READ ioctl reports the low battery condition. Still,
pcf8523_rtc_read_time() happily returns invalid dates in this case.
Check the battery health on pcf8523_rtc_read_time() to avoid that.

Reported-by: Erik Čuk <erik....@domel.com>
Signed-off-by: Baruch Siach <bar...@tkos.co.il>
Signed-off-by: Alexandre Belloni <alexandre.bell...@bootlin.com>
Signed-off-by: Greg Kroah-Hartman <gre...@linuxfoundation.org>

---
 drivers/rtc/rtc-pcf8523.c |   32 ++++++++++++++++++++++++--------
 1 file changed, 24 insertions(+), 8 deletions(-)

--- a/drivers/rtc/rtc-pcf8523.c
+++ b/drivers/rtc/rtc-pcf8523.c
@@ -82,6 +82,18 @@ static int pcf8523_write(struct i2c_clie
        return 0;
 }
 
+static int pcf8523_voltage_low(struct i2c_client *client)
+{
+       u8 value;
+       int err;
+
+       err = pcf8523_read(client, REG_CONTROL3, &value);
+       if (err < 0)
+               return err;
+
+       return !!(value & REG_CONTROL3_BLF);
+}
+
 static int pcf8523_select_capacitance(struct i2c_client *client, bool high)
 {
        u8 value;
@@ -164,6 +176,14 @@ static int pcf8523_rtc_read_time(struct
        struct i2c_msg msgs[2];
        int err;
 
+       err = pcf8523_voltage_low(client);
+       if (err < 0) {
+               return err;
+       } else if (err > 0) {
+               dev_err(dev, "low voltage detected, time is unreliable\n");
+               return -EINVAL;
+       }
+
        msgs[0].addr = client->addr;
        msgs[0].flags = 0;
        msgs[0].len = 1;
@@ -248,17 +268,13 @@ static int pcf8523_rtc_ioctl(struct devi
                             unsigned long arg)
 {
        struct i2c_client *client = to_i2c_client(dev);
-       u8 value;
-       int ret = 0, err;
+       int ret;
 
        switch (cmd) {
        case RTC_VL_READ:
-               err = pcf8523_read(client, REG_CONTROL3, &value);
-               if (err < 0)
-                       return err;
-
-               if (value & REG_CONTROL3_BLF)
-                       ret = 1;
+               ret = pcf8523_voltage_low(client);
+               if (ret < 0)
+                       return ret;
 
                if (copy_to_user((void __user *)arg, &ret, sizeof(int)))
                        return -EFAULT;