linux-kernel - Re: [PATCH net-next 3/3] net: ethtool: tsconfig: Re-configure hwtstamp upon provider change

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Message-ID: <20251015144526.23e55ee0@kmaincent-XPS-13-7390>
Date: Wed, 15 Oct 2025 14:45:26 +0200
From: Kory Maincent <kory.maincent@...tlin.com>
To: Maxime Chevallier <maxime.chevallier@...tlin.com>
Cc: Alexandre Torgue <alexandre.torgue@...s.st.com>, Jose Abreu
 <joabreu@...opsys.com>, Andrew Lunn <andrew+netdev@...n.ch>,
 davem@...emloft.net, Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski
 <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, Maxime Coquelin
 <mcoquelin.stm32@...il.com>, Richard Cochran <richardcochran@...il.com>,
 Russell King <linux@...linux.org.uk>, Alexis Lothoré
 <alexis.lothore@...tlin.com>, Thomas Petazzoni
 <thomas.petazzoni@...tlin.com>, netdev@...r.kernel.org,
 linux-stm32@...md-mailman.stormreply.com,
 linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH net-next 3/3] net: ethtool: tsconfig: Re-configure
 hwtstamp upon provider change

On Wed, 15 Oct 2025 12:27:23 +0200
Maxime Chevallier <maxime.chevallier@...tlin.com> wrote:

> When a hwprov timestamping source is changed, but without updating the
> timestamping parameters, we may want to reconfigure the timestamping
> source to enable the new provider.
> 
> This is especially important if the same HW unit implements 2 providers,
> a precise and an approx one. In this case, we need to make sure we call
> the hwtstamp_set operation for the newly selected provider.

This is a design choice.
Do we want to preserve the hwtstamp config if only the hwtstamp source is
changed from ethtool?
If we want to configure the new source to the old source config we will also
need to remove this condition:
https://elixir.bootlin.com/linux/v6.17.1/source/net/ethtool/tsconfig.c#L339 

I do not really have a strong opinion on this, let's discuss which behavior we
prefer.

Regards,
-- 
Köry Maincent, Bootlin
Embedded Linux and kernel engineering
https://bootlin.com