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

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Date: Wed, 22 Nov 2023 09:55:25 -0800
From: Jakub Kicinski <kuba@...nel.org>
To: Vladimir Oltean <vladimir.oltean@....com>
Cc: Köry Maincent <kory.maincent@...tlin.com>, 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 Wed, 22 Nov 2023 18:59:55 +0200 Vladimir Oltean wrote:
> I wouldn't be so sure. The alternative interpretation "for PTP, give me
> timestamps from both sources" also sounds reasonable for the distant
> future where that will be possible (with proper cmsg identification).
> But I don't see how to distinguish the two - the filters, expressed in
> these terms, would be the same.

We can add an attribute that explicitly says that the configuration
is only requesting one stamp. But feels like jumping the gun at this
stage, given we have no other option to express there.

> So the ptp4l source code would have to be modified to still work with
> the same precision as before? I'm not seeing this through.

We can do the opposite and add a socket flag which says "DMA is okay".