Re: [PATCH] rtc: rs5c372: add offset correction support

[Camel Guo <camelg@axis.com>]

On 11/30/21 10:50 AM, Camel Guo wrote:
> From: Camel Guo <camelg@axis.com>
> 
> This commit adds support of offset correction by configuring the
> oscillation adjustment register of rs5c372.
> 
> Signed-off-by: Camel Guo <camelg@axis.com>
> ---
>   drivers/rtc/rtc-rs5c372.c | 80 +++++++++++++++++++++++++++++++++++++++
>   1 file changed, 80 insertions(+)
> 
> diff --git a/drivers/rtc/rtc-rs5c372.c b/drivers/rtc/rtc-rs5c372.c
> index 80980414890c..77027498cad5 100644
> --- a/drivers/rtc/rtc-rs5c372.c
> +++ b/drivers/rtc/rtc-rs5c372.c
> @@ -30,6 +30,8 @@
>   #define RS5C372_REG_TRIM        7
>   #       define RS5C372_TRIM_XSL         0x80
>   #       define RS5C372_TRIM_MASK        0x7F
> +#      define RS5C372_TRIM_DEV         (1 << 7)
> +#      define RS5C372_TRIM_DECR        (1 << 6)
> 
>   #define RS5C_REG_ALARM_A_MIN    8                       /* or ALARM_W */
>   #define RS5C_REG_ALARM_A_HOURS  9
> @@ -485,6 +487,82 @@ static int rs5c372_rtc_proc(struct device *dev, 
> struct seq_file *seq)
>   #define rs5c372_rtc_proc        NULL
>   #endif
> 
> +static int rs5c372_read_offset(struct device *dev, long *offset)
> +{
> +       struct rs5c372 *rs5c = i2c_get_clientdata(to_i2c_client(dev));
> +       int addr = RS5C_ADDR(RS5C372_REG_TRIM);
> +       unsigned char val = i2c_smbus_read_byte_data(rs5c->client, addr);
> +       long ppb_per_step = (val & RS5C372_TRIM_DEV) ? 1017 : 3052;
> +       unsigned char decr = val & RS5C372_TRIM_DECR;
> +
> +       /* Only bits[0:5] repsents the time counts */
> +       val &= 0x3F;
> +
> +       /* If bits[1:5] are all 0, it means no increment or decrement */
> +       if (!(val & 0x3E)) {
> +               *offset = 0;
> +       } else {
> +               if (decr)
> +                       *offset = -(((~val) & 0x3F) + 1) * ppb_per_step;
> +               else
> +                       *offset = (val - 1) * ppb_per_step;
> +       }
> +
> +       return 0;
> +}
> +
> +static int rs5c372_set_offset(struct device *dev, long offset)
> +{
> +       struct rs5c372 *rs5c = i2c_get_clientdata(to_i2c_client(dev));
> +       int addr = RS5C_ADDR(RS5C372_REG_TRIM);
> +       unsigned char val = RS5C372_TRIM_DEV;
> +       long steps = 0;
> +
> +       /*
> +        * Check if it is possible to use high resolution mode (DEV=1). 
> In this
> +        * mode, the minimum resolution is 2 / (32768 * 20 * 3), which 
> is about
> +        * 1017 ppb
> +        */
> +       steps = DIV_ROUND_CLOSEST(offset, 1017);
> +       if (steps > 0x3E || steps < -0x3E) {
> +               /*
> +                * offset is out of the range of high resolution mode. 
> Try to
> +                * use low resolution mode (DEV=0). In this mode, the 
> minimum
> +                * resolution is 2 / (32768 * 20), which is about 3052 ppb.
> +                */
> +               val &= ~RS5C372_TRIM_DEV;
> +               steps = DIV_ROUND_CLOSEST(offset, 3052);
> +
> +               if (steps > 0x3E || steps < -0x3E)
> +                       return -ERANGE;
> +       }
> +
> +       if (steps > 0) {
> +               val |= steps + 1;
> +       } else {
> +               val |= RS5C372_TRIM_DECR;
> +               val |= (~(-steps - 1)) & 0x3F;
> +       }
> +
> +       if (!steps || !(val & 0x3E)) {
> +               /*
> +                * if offset is too small, set oscillation adjustment 
> register
> +                * with the default values, which means no increment or
> +                * decrement.
> +                */
> +               val = 0;
> +       }
> +
> +       dev_dbg(&rs5c->client->dev, "write 0x%x for offset %ld\n", val, 
> offset);
> +
> +       if (i2c_smbus_write_byte_data(rs5c->client, addr, val) < 0) {
> +               dev_err(&rs5c->client->dev, "failed to write 0x%x to reg 
> %d\n", val, addr);
> +               return -EIO;
> +       }
> +
> +       return 0;
> +}
> +
>   static const struct rtc_class_ops rs5c372_rtc_ops = {
>           .proc           = rs5c372_rtc_proc,
>           .read_time      = rs5c372_rtc_read_time,
> @@ -492,6 +570,8 @@ static const struct rtc_class_ops rs5c372_rtc_ops = {
>           .read_alarm     = rs5c_read_alarm,
>           .set_alarm      = rs5c_set_alarm,
>           .alarm_irq_enable = rs5c_rtc_alarm_irq_enable,
> +       .read_offset    = rs5c372_read_offset,
> +       .set_offset     = rs5c372_set_offset,
>   };
> 
>   #if IS_ENABLED(CONFIG_RTC_INTF_SYSFS)
> -- 
> 2.20.1
> 

Just realize that the oscillation adjustment registers of r2*, rs5c* are 
not totally same and all of these differences need to be handled in 
different way. Hence this patch needs to be updated to cover all cases.