From d4caec563cc89319516a29a9b3c40ec302925d7a Mon Sep 17 00:00:00 2001 From: Phil Elwell Date: Mon, 29 Oct 2018 14:45:45 +0000 Subject: [PATCH] rtc: pcf8523: Fix oscillator stop bit handling See: https://github.com/raspberrypi/firmware/issues/1065 Signed-off-by: Phil Elwell --- drivers/rtc/rtc-pcf8523.c | 29 +++++++++++++++++++++++++++-- 1 file changed, 27 insertions(+), 2 deletions(-) --- a/drivers/rtc/rtc-pcf8523.c +++ b/drivers/rtc/rtc-pcf8523.c @@ -100,6 +100,7 @@ static int pcf8523_rtc_read_time(struct { struct pcf8523 *pcf8523 = dev_get_drvdata(dev); u8 regs[7]; + u32 value; int err; err = regmap_bulk_read(pcf8523->regmap, PCF8523_REG_SECONDS, regs, @@ -107,8 +108,32 @@ static int pcf8523_rtc_read_time(struct if (err < 0) return err; - if (regs[0] & 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[0] & 0x7f); tm->tm_min = bcd2bin(regs[1] & 0x7f);