diff options
| -rw-r--r-- | drivers/rtc/rtc-pcf2123.c | 57 |
1 files changed, 57 insertions, 0 deletions
diff --git a/drivers/rtc/rtc-pcf2123.c b/drivers/rtc/rtc-pcf2123.c index d9a44ad1239b..da27738b1242 100644 --- a/drivers/rtc/rtc-pcf2123.c +++ b/drivers/rtc/rtc-pcf2123.c @@ -100,6 +100,7 @@ /* PCF2123_REG_OFFSET BITS */ #define OFFSET_SIGN_BIT BIT(6) /* 2's complement sign bit */ #define OFFSET_COARSE BIT(7) /* Coarse mode offset */ +#define OFFSET_STEP (2170) /* Offset step in parts per billion */ /* READ/WRITE ADDRESS BITS */ #define PCF2123_WRITE BIT(4) @@ -206,6 +207,59 @@ static ssize_t pcf2123_store(struct device *dev, struct device_attribute *attr, return count; } +static int pcf2123_read_offset(struct device *dev, long *offset) +{ + int ret; + s8 reg; + + ret = pcf2123_read(dev, PCF2123_REG_OFFSET, ®, 1); + if (ret < 0) + return ret; + + if (reg & OFFSET_COARSE) + reg <<= 1; /* multiply by 2 and sign extend */ + else + reg |= (reg & OFFSET_SIGN_BIT) << 1; /* sign extend only */ + + *offset = ((long)reg) * OFFSET_STEP; + + return 0; +} + +/* + * The offset register is a 7 bit signed value with a coarse bit in bit 7. + * The main difference between the two is normal offset adjusts the first + * second of n minutes every other hour, with 61, 62 and 63 being shoved + * into the 60th minute. + * The coarse adjustment does the same, but every hour. + * the two overlap, with every even normal offset value corresponding + * to a coarse offset. Based on this algorithm, it seems that despite the + * name, coarse offset is a better fit for overlapping values. + */ +static int pcf2123_set_offset(struct device *dev, long offset) +{ + s8 reg; + + if (offset > OFFSET_STEP * 127) + reg = 127; + else if (offset < OFFSET_STEP * -128) + reg = -128; + else + reg = (s8)((offset + (OFFSET_STEP >> 1)) / OFFSET_STEP); + + /* choose fine offset only for odd values in the normal range */ + if (reg & 1 && reg <= 63 && reg >= -64) { + /* Normal offset. Clear the coarse bit */ + reg &= ~OFFSET_COARSE; + } else { + /* Coarse offset. Divide by 2 and set the coarse bit */ + reg >>= 1; + reg |= OFFSET_COARSE; + } + + return pcf2123_write_reg(dev, PCF2123_REG_OFFSET, reg); +} + static int pcf2123_rtc_read_time(struct device *dev, struct rtc_time *tm) { u8 rxbuf[7]; @@ -314,6 +368,9 @@ static int pcf2123_reset(struct device *dev) static const struct rtc_class_ops pcf2123_rtc_ops = { .read_time = pcf2123_rtc_read_time, .set_time = pcf2123_rtc_set_time, + .read_offset = pcf2123_read_offset, + .set_offset = pcf2123_set_offset, + }; static int pcf2123_probe(struct spi_device *spi) |