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

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Message-ID: <acfc8c63-4434-4738-84a9-00360e70c773@lunn.ch>
Date: Wed, 10 Sep 2025 18:13:21 +0200
From: Andrew Lunn <andrew@...n.ch>
To: Ivan Vecera <ivecera@...hat.com>
Cc: netdev@...r.kernel.org, Prathosh Satish <Prathosh.Satish@...rochip.com>,
	Jiri Pirko <jiri@...nulli.us>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	Simon Horman <horms@...nel.org>, Jonathan Corbet <corbet@....net>,
	"open list:DOCUMENTATION" <linux-doc@...r.kernel.org>,
	open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH net-next] dpll: zl3073x: Allow to use custom phase
 measure averaging factor

On Wed, Sep 10, 2025 at 12:32:21PM +0200, 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@...rochip.com>
> Signed-off-by: Ivan Vecera <ivecera@...hat.com>
> ---
>  Documentation/networking/devlink/zl3073x.rst |  4 ++
>  drivers/dpll/zl3073x/core.c                  |  6 +-
>  drivers/dpll/zl3073x/core.h                  |  8 ++-
>  drivers/dpll/zl3073x/devlink.c               | 67 ++++++++++++++++++++
>  4 files changed, 82 insertions(+), 3 deletions(-)
> 
> diff --git a/Documentation/networking/devlink/zl3073x.rst b/Documentation/networking/devlink/zl3073x.rst
> index 4b6cfaf386433..ddd159e39e616 100644
> --- a/Documentation/networking/devlink/zl3073x.rst
> +++ b/Documentation/networking/devlink/zl3073x.rst
> @@ -20,6 +20,10 @@ Parameters
>       - driverinit
>       - Set the clock ID that is used by the driver for registering DPLL devices
>         and pins.
> +   * - ``phase_offset_avg_factor``
> +     - runtime
> +     - Set the factor for the exponential moving average used by DPLL phase
> +       measurement block. The value has to be in range <0, 15>.

Maybe put the text in the commit message here as well?

      Andrew