The XT digital calibration feature allows to improve the RTC accuracy, using a Distributed Digital Calibration function. See ch. 5.9.1 of AB08XX Series Ultra Low Power RTC IC User's Guide https://abracon.com/realtimeclock/AB08XX-Application-Manual.pdf Signed-off-by: Kirill Kapranov <kirill.kapranov@xxxxxxxxxxxxxx> --- drivers/rtc/rtc-abx80x.c | 145 +++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 145 insertions(+) diff --git a/drivers/rtc/rtc-abx80x.c b/drivers/rtc/rtc-abx80x.c index 153d89b56da9..e13fa88e87a5 100644 --- a/drivers/rtc/rtc-abx80x.c +++ b/drivers/rtc/rtc-abx80x.c @@ -54,6 +54,9 @@ #define ABX8XX_REG_SQW 0x13 #define ABX8XX_SQW_MODE_BITS 5 +#define ABX8XX_REG_CAL_XT 0x14 +#define ABX8XX_CAL_XT_OFFSETX_MASK GENMASK(6, 0) + #define ABX8XX_REG_CD_TIMER_CTL 0x18 #define ABX8XX_REG_OSC 0x1c @@ -120,6 +123,22 @@ struct abx80x_priv { struct watchdog_device wdog; }; +union abx8xx_reg_cal_xt { + struct { + int offsetx:7; + unsigned int cmdx:1; + }; + int val; +} __packed; + +union abx8xx_reg_oss { + struct { + int:6; + unsigned int xtcal:2; + }; + int val; +} __packed; + union abx8xx_reg_sqw { struct { unsigned int sqws:5; @@ -498,6 +517,123 @@ static ssize_t oscillator_show(struct device *dev, static DEVICE_ATTR_RW(oscillator); +static const int xt_freq_nom = 32768000; //Nominal XT frequency 32 kHz in mHz + +static int xt_frequency_set(struct i2c_client *client, u32 xt_freq) +{ + int retval; + long Adj; + union abx8xx_reg_cal_xt reg_cal_xt; + union abx8xx_reg_oss reg_oss; + + retval = i2c_smbus_read_byte_data(client, ABX8XX_REG_OSS); + if (retval < 0) + goto err; + reg_oss.val = retval; + + Adj = (xt_freq_nom - (int)xt_freq) * 16 / 1000; + if (Adj < -320) { + dev_err(&client->dev, + "The XT oscillator is too fast to be adjusted\n"); + return -ERANGE; + } else if (Adj < -256) { + reg_oss.xtcal = 3; + reg_cal_xt.cmdx = 1; + reg_cal_xt.offsetx = (Adj + 192) / 2; + } else if (Adj < -192) { + reg_oss.xtcal = 3; + reg_cal_xt.cmdx = 0; + reg_cal_xt.offsetx = Adj + 192; + } else if (Adj < -128) { + reg_oss.xtcal = 2; + reg_cal_xt.cmdx = 0; + reg_cal_xt.offsetx = Adj + 128; + } else if (Adj < -64) { + reg_oss.xtcal = 1; + reg_cal_xt.cmdx = 0; + reg_cal_xt.offsetx = Adj + 64; + } else if (Adj < 64) { + reg_oss.xtcal = 0; + reg_cal_xt.cmdx = 0; + reg_cal_xt.offsetx = Adj; + } else if (Adj < 128) { + reg_oss.xtcal = 0; + reg_cal_xt.cmdx = 1; + reg_cal_xt.offsetx = Adj / 2; + } else { + dev_err(&client->dev, + "The XT oscillator is too slow to be adjusted\n"); + return -ERANGE; + } + + retval = i2c_smbus_write_byte_data(client, ABX8XX_REG_OSS, + reg_oss.val); + if (retval < 0) + goto err; + + retval = i2c_smbus_write_byte_data(client, ABX8XX_REG_CAL_XT, + reg_cal_xt.val); + if (retval < 0) + goto err; + + return 0; +err: + dev_err(&client->dev, "Failed to access calibration data\n"); + return retval; +} + +static ssize_t xt_frequency_store(struct device *dev, + struct device_attribute *attr, + const char *buf, size_t count) +{ + int retval; + unsigned long xt_freq; + + retval = kstrtoul(buf, 10, &xt_freq); + if (retval < 0) { + dev_err(dev, "Invalid value of oscillator frequency\n"); + return -EINVAL; + } + + dev_info(dev, "Computed xt osc drift is %li ppm\n", + 1000000l * ((long)xt_freq - xt_freq_nom) / xt_freq_nom); + + retval = xt_frequency_set(to_i2c_client(dev->parent), xt_freq); + if (retval) + return retval; + return count; +} + +static DEVICE_ATTR_WO(xt_frequency); + +static ssize_t xt_calibration_show(struct device *dev, + struct device_attribute *attr, char *buf) +{ + int retval; + union abx8xx_reg_cal_xt reg_cal_xt; + union abx8xx_reg_oss reg_oss; + struct i2c_client *client = to_i2c_client(dev->parent); + + retval = i2c_smbus_read_byte_data(client, ABX8XX_REG_OSS); + if (retval < 0) + goto err; + reg_oss.val = retval; + + retval = i2c_smbus_read_byte_data(client, ABX8XX_REG_CAL_XT); + if (retval < 0) + goto err; + reg_cal_xt.val = retval; + + return sprintf(buf, "XTCAL %x\nCMDX %x\nOFFSETX %i = 0x%lx\n", + reg_oss.xtcal, reg_cal_xt.cmdx, reg_cal_xt.offsetx, + reg_cal_xt.offsetx & ABX8XX_CAL_XT_OFFSETX_MASK); +err: + dev_err(dev, "Failed to read calibration data\n"); + sprintf(buf, "\n"); + return retval; +} +static DEVICE_ATTR_RO(xt_calibration); + #define SQFS_COUNT (1 << ABX8XX_SQW_MODE_BITS) /* The index of the array is the value to be written to the 'Square Wave Function * Select' register to make the RTC generate the required square wave. @@ -611,6 +747,8 @@ static struct attribute *rtc_calib_attrs[] = { &dev_attr_autocalibration.attr, &dev_attr_oscillator.attr, &dev_attr_sqw.attr, + &dev_attr_xt_calibration.attr, + &dev_attr_xt_frequency.attr, NULL, }; @@ -809,6 +947,7 @@ static int abx80x_probe(struct i2c_client *client, unsigned int wafer; unsigned int uid; const char *sqw_mode_name; + unsigned int xt_freq; if (!i2c_check_functionality(client->adapter, I2C_FUNC_I2C)) return -ENODEV; @@ -923,6 +1062,12 @@ static int abx80x_probe(struct i2c_client *client, abx80x_enable_trickle_charger(client, trickle_cfg); } + if (!of_property_read_u32(np, "xt-frequency", &xt_freq)) { + dev_info(&client->dev, "Calibrate XT %d mHz:\n", + xt_freq); + xt_frequency_set(client, xt_freq); + } + if (!of_property_read_string(np, "sqw", &sqw_mode_name)) sqw_set(client, sqw_mode_name); -- 2.11.0
