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

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Date: Mon, 20 Nov 2023 12:52:55 +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

Hi Köry,

On Mon, Nov 20, 2023 at 10:44:39AM +0100, Köry Maincent wrote:
> On Sat, 18 Nov 2023 18:34:33 -0800
> Jakub Kicinski <kuba@...nel.org> wrote:
> 
> > On Tue, 14 Nov 2023 12:28:43 +0100 Kory Maincent wrote:
> > > +	if (!tb[ETHTOOL_A_TS_LAYER])
> > > +		return 0;  
> > 
> > GENL_REQ_ATTR_CHECK(), not sure why anyone would issue this command
> > without any useful attr.
> > 
> > > +	/* Disable time stamping in the current layer. */
> > > +	if (netif_device_present(dev) &&
> > > +	    (dev->ts_layer == PHY_TIMESTAMPING ||
> > > +	    dev->ts_layer == MAC_TIMESTAMPING)) {
> > > +		ret = dev_set_hwtstamp_phylib(dev, &config, info->extack);
> > > +		if (ret < 0)
> > > +			return ret;  
> > 
> > So you only support PHYLIB?
> > 
> > The semantics need to be better documented :(
> 
> Yes as we don't really know how each MAC deal with the timestamping
> before ndo_hwstamp_get/set. Using phylib only allows us to be sure these NDO are
> implemented and the management of timestamping is coherent in the MAC. Also It
> will push people to move on to these NDOs.
> 
> Ok I will add documentation.
> 
> -- 
> Köry Maincent, Bootlin
> Embedded Linux and kernel engineering
> https://bootlin.com/

When Jakub says "the semantics need to be better documented", I'm also
thinking of a different direction.

>From what I understand, Maxime is working on representing multiple
phylib PHYs in the UAPI:
https://patchwork.kernel.org/project/netdevbpf/cover/20231117162323.626979-1-maxime.chevallier@bootlin.com/

Does your UAPI proposal make it possible in any way to select
timestamping in phylib PHY A rather than PHY B? Or do you think it is
extensible to support that, somehow?