linux-kernel - Re: [PATCH net-next] dpll: expose fractional frequency offset in ppt

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Message-ID: <sxjsuxqsgx2etc2t3hd4v7wpffdoe6e5epacktdobwynyv7bru@ra37na5aqxyx>
Date: Thu, 29 Jan 2026 13:15:05 +0100
From: Jiri Pirko <jiri@...nulli.us>
To: Ivan Vecera <ivecera@...hat.com>
Cc: netdev@...r.kernel.org, Donald Hunter <donald.hunter@...il.com>, 
	Jakub Kicinski <kuba@...nel.org>, "David S. Miller" <davem@...emloft.net>, 
	Eric Dumazet <edumazet@...gle.com>, Paolo Abeni <pabeni@...hat.com>, Simon Horman <horms@...nel.org>, 
	Vadim Fedorenko <vadim.fedorenko@...ux.dev>, Arkadiusz Kubalewski <arkadiusz.kubalewski@...el.com>, 
	Prathosh Satish <Prathosh.Satish@...rochip.com>, Saeed Mahameed <saeedm@...dia.com>, 
	Leon Romanovsky <leon@...nel.org>, Tariq Toukan <tariqt@...dia.com>, Mark Bloch <mbloch@...dia.com>, 
	Andrew Lunn <andrew+netdev@...n.ch>, Petr Oros <poros@...hat.com>, 
	open list <linux-kernel@...r.kernel.org>, 
	"open list:MELLANOX MLX5 core VPI driver" <linux-rdma@...r.kernel.org>
Subject: Re: [PATCH net-next] dpll: expose fractional frequency offset in ppt

Mon, Jan 26, 2026 at 05:22:51PM +0100, ivecera@...hat.com wrote:
>Currently, the dpll subsystem exports the fractional frequency offset
>(FFO) in parts per million (ppm). This granularity is insufficient for
>high-precision synchronization scenarios which often require parts per
>trillion (ppt) resolution.
>
>Add a new netlink attribute DPLL_A_PIN_FRACTIONAL_FREQUENCY_OFFSET_PPT
>to expose the FFO in ppt.
>
>Update the dpll netlink core to expect the driver-provided FFO value
>to be in ppt. To maintain backward compatibility with existing userspace
>tools, populate the legacy DPLL_A_PIN_FRACTIONAL_FREQUENCY_OFFSET
>attribute by dividing the new ppt value by 1,000,000.
>
>Update the zl3073x and mlx5 drivers to provide the FFO value in ppt:
>- zl3073x: adjust the fixed-point calculation to produce ppt (10^12)
>  instead of ppm (10^6).
>- mlx5: scale the existing ppm value by 1,000,000.
>
>Signed-off-by: Ivan Vecera <ivecera@...hat.com>

Reviewed-by: Jiri Pirko <jiri@...dia.com>