Re: [PATCH net-next] dpll: zl3073x: Allow to use custom phase measure averaging factor

[Ivan Vecera <ivecera@redhat.com>]

On 10. 09. 25 2:34 odp., Vadim Fedorenko wrote:
> On 10.09.2025 11:32, Ivan Vecera wrote:
>> The DPLL phase measurement block uses an exponential moving average,
>> calculated using the following equation:
>>
>>                         2^N - 1                1
>> curr_avg = prev_avg * --------- + new_val * -----
>>                           2^N                 2^N
>>
>> Where curr_avg is phase offset reported by the firmware to the driver,
>> prev_avg is previous averaged value and new_val is currently measured
>> value for particular reference.
>>
>> New measurements are taken approximately 40 Hz or at the frequency of
>> the reference (whichever is lower).
>>
>> The driver currently uses the averaging factor N=2 which prioritizes
>> a fast response time to track dynamic changes in the phase. But for
>> applications requiring a very stable and precise reading of the average
>> phase offset, and where rapid changes are not expected, a higher factor
>> would be appropriate.
>>
>> Add devlink device parameter phase_offset_avg_factor to allow a user
>> set tune the averaging factor via devlink interface.
>>
>> Tested-by: Prathosh Satish <Prathosh.Satish@microchip.com>
>> Signed-off-by: Ivan Vecera <ivecera@redhat.com>
> 
> [...]
> 
>> +static int
>> +zl3073x_devlink_param_phase_avg_factor_set(struct devlink *devlink, 
>> u32 id,
>> +                       struct devlink_param_gset_ctx *ctx,
>> +                       struct netlink_ext_ack *extack)
>> +{
>> +    struct zl3073x_dev *zldev = devlink_priv(devlink);
>> +    u8 avg_factor, dpll_meas_ctrl;
>> +    int rc;
>> +
>> +    /* Read DPLL phase measurement control register */
>> +    rc = zl3073x_read_u8(zldev, ZL_REG_DPLL_MEAS_CTRL, &dpll_meas_ctrl);
>> +    if (rc)
>> +        return rc;
>> +
>> +    /* Convert requested factor to register value */
>> +    if (ctx->val.vu8 < 15)
>> +        avg_factor = ctx->val.vu8 + 1;
>> +    else
>> +        avg_factor = 0;
>> +
> 
> This looks like avg_factor = (ctx->val.vu8 + 1) & 0x0f;
> The same logic can be applied for get() function assuming we are aware of
> unsigned roll-over...

Yes, I know about this trick but I wanted to use more readable code and
leave potential optimization to the compiler.

Ivan