rtc: pcf8523: Fix oscillator stop bit handling

See: https://github.com/raspberrypi/firmware/issues/1065

Signed-off-by: Phil Elwell <phil@raspberrypi.com>

diff --git a/drivers/rtc/rtc-pcf8523.c b/drivers/rtc/rtc-pcf8523.c
index d1efde3..6f95c7c 100644 (file)
--- a/drivers/rtc/rtc-pcf8523.c
+++ b/drivers/rtc/rtc-pcf8523.c
@@ -100,6 +100,7 @@ static int pcf8523_rtc_read_time(struct device *dev, struct rtc_time *tm)
 {
        struct pcf8523 *pcf8523 = dev_get_drvdata(dev);
        u8 regs[10];
+       u32 value;
        int err;
 
        err = regmap_bulk_read(pcf8523->regmap, PCF8523_REG_CONTROL1, regs,
@@ -110,6 +111,33 @@ static int pcf8523_rtc_read_time(struct device *dev, struct rtc_time *tm)
        if ((regs[0] & PCF8523_CONTROL1_STOP) || (regs[3] & PCF8523_SECONDS_OS))
                return -EINVAL;
 
+       if (regs[0] & PCF8523_SECONDS_OS) {
+               /*
+                * If the oscillator was stopped, try to clear the flag. Upon
+                * power-up the flag is always set, but if we cannot clear it
+                * the oscillator isn't running properly for some reason. The
+                * sensible thing therefore is to return an error, signalling
+                * that the clock cannot be assumed to be correct.
+                */
+
+               regs[0] &= ~PCF8523_SECONDS_OS;
+
+               err = regmap_write(pcf8523->regmap, PCF8523_REG_SECONDS,
+                                  regs[0]);
+               if (err < 0)
+                       return err;
+
+               err = regmap_read(pcf8523->regmap, PCF8523_REG_SECONDS,
+                                 &value);
+               if (err < 0)
+                       return err;
+
+               if (value & PCF8523_SECONDS_OS)
+                       return -EAGAIN;
+
+               regs[0] = value;
+       }
+
        tm->tm_sec = bcd2bin(regs[3] & 0x7f);
        tm->tm_min = bcd2bin(regs[4] & 0x7f);
        tm->tm_hour = bcd2bin(regs[5] & 0x3f);