netdev - Re: [PATCH net-next v7 15/16] net: ethtool: ts: Let the active time stamping layer be selectable

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Message-ID: <20231124195709.wkhplnhtpxf75a6n@skbuf>
Date: Fri, 24 Nov 2023 21:57:09 +0200
From: Vladimir Oltean <vladimir.oltean@....com>
To: Köry Maincent <kory.maincent@...tlin.com>
Cc: Jakub Kicinski <kuba@...nel.org>,
	Florian Fainelli <florian.fainelli@...adcom.com>,
	Broadcom internal kernel review list <bcm-kernel-feedback-list@...adcom.com>,
	Andrew Lunn <andrew@...n.ch>,
	Heiner Kallweit <hkallweit1@...il.com>,
	Russell King <linux@...linux.org.uk>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>, Paolo Abeni <pabeni@...hat.com>,
	Richard Cochran <richardcochran@...il.com>,
	Radu Pirea <radu-nicolae.pirea@....nxp.com>,
	Jay Vosburgh <j.vosburgh@...il.com>,
	Andy Gospodarek <andy@...yhouse.net>,
	Nicolas Ferre <nicolas.ferre@...rochip.com>,
	Claudiu Beznea <claudiu.beznea@...on.dev>,
	Willem de Bruijn <willemdebruijn.kernel@...il.com>,
	Jonathan Corbet <corbet@....net>,
	Horatiu Vultur <horatiu.vultur@...rochip.com>,
	UNGLinuxDriver@...rochip.com, Simon Horman <horms@...nel.org>,
	Thomas Petazzoni <thomas.petazzoni@...tlin.com>,
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-doc@...r.kernel.org,
	Maxime Chevallier <maxime.chevallier@...tlin.com>
Subject: Re: [PATCH net-next v7 15/16] net: ethtool: ts: Let the active time
 stamping layer be selectable

On Fri, Nov 24, 2023 at 06:34:31PM +0100, Köry Maincent wrote:
> Would it break things if both ioctls and netlink can get and set the
> hwtstamps configuration?

Uhm, obviously? It would break things if ioctl and netlink were _not_
freely interchangeable, and you couldn't see in a ioctl GET what got set
through a netlink SET.

> It is only configuration. Both happen under rtnl_lock it should be
> alright.

Yeah, but you always need to keep the API interchangeability in mind
during the implementation.

> The question is which hwtstamp provider will the original ioctls be able to
> change? Maybe the default one (MAC with phy whitelist) and only this one.

TL;DR: yeah.

Remember one single rule and go from there: new development should not
change established setups. So SIOCSHWSTAMPs should continue to behave
"as before".

This is also the exact reason why I asked for the phy whitelist. The
introduction of CONFIG_NETWORK_PHY_TIMESTAMPING introduced exactly that:
a breaking change in the mode in which deployed setups operate.

> > But by all means, still hold a poll if you want to. I would vote for
> > ethtool netlink, not because it's great, just because I don't have a
> > better alternative to propose.
> 
> If you agree on that choice, let's go. Jakub and your are the most proactive
> reviewers in this patch series. Willem you are the timestamping maintainer do
> you also agree on this? 
> If anyone have another proposition let them speak now, or forever remain
> silent! ;)

Hmm, proactive means doing stuff in anticipation of being requested to
do it. I'd use the work "active" at most...