netdev - Re: [RFC 0/3] ptp: Add esterror support

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Message-ID: <Zr17vLsheLjXKm3Y@hoboy.vegasvil.org>
Date: Wed, 14 Aug 2024 20:53:32 -0700
From: Richard Cochran <richardcochran@...il.com>
To: Maciek Machnikowski <maciek@...hnikowski.net>
Cc: Andrew Lunn <andrew@...n.ch>,
	Vadim Fedorenko <vadim.fedorenko@...ux.dev>, netdev@...r.kernel.org,
	jacob.e.keller@...el.com, darinzon@...zon.com, kuba@...nel.org
Subject: Re: [RFC 0/3] ptp: Add esterror support

On Wed, Aug 14, 2024 at 05:08:24PM +0200, Maciek Machnikowski wrote:

> The esterror should return the error calculated by the device. There is
> no standard defining this, but the simplest implementation can put the
> offset calculated by the ptp daemon, or the offset to the nearest PPS in
> cases where PPS is used as a source of time

So user space produces the number, and other user space consumes it?

Sounds like it should say in user space, shared over some IPC, like
PTP management messages for example.

> the ADJ_ESTERROR to push the error estimate to the device. The device
> will then be able to
> a. provide that information to hardware clocks on different functions

Not really, because there no in-kernel API for one device to query
another.  At least you didn't provide one.  Looks like you mean that
some user space program sets the value, and another program reads it
to share it with other devices?

> b. prevent time-dependent functionalities from acting when a clock
> shifts beyond a predefined limit.

This can be controlled by the user space stack.  For example, "if
estimated error exceeds threshold, disable PPS output".

Thanks,
Richard