rtc: pcf8523: don't return invalid date when battery is low

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.cuk@domel.com>
Signed-off-by: Baruch Siach <baruch@tkos.co.il>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>

diff --git a/drivers/rtc/rtc-pcf8523.c b/drivers/rtc/rtc-pcf8523.c
index 453615f8ac9a012ea0022227f947f5778c477fdf..3fcd2cbafc84570d9c1738e1c60081ad944a124c 100644 (file)
--- a/drivers/rtc/rtc-pcf8523.c
+++ b/drivers/rtc/rtc-pcf8523.c
@@ -85,6 +85,18 @@ static int pcf8523_write(struct i2c_client *client, u8 reg, u8 value)
        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;
@@ -167,6 +179,14 @@ static int pcf8523_rtc_read_time(struct device *dev, struct rtc_time *tm)
        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;
@@ -251,17 +271,13 @@ static int pcf8523_rtc_ioctl(struct device *dev, unsigned int cmd,
                             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;