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    Subject[PATCH 4.9 089/117] rtc: pcf8523: dont return invalid date when battery is low
    Date
    From: Baruch Siach <baruch@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.cuk@domel.com>
    Signed-off-by: Baruch Siach <baruch@tkos.co.il>
    Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
    Signed-off-by: Greg Kroah-Hartman <gregkh@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;

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