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 12:14:40 +0100
From: Köry Maincent <kory.maincent@...tlin.com>
To: Vladimir Oltean <vladimir.oltean@....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 Mon, 20 Nov 2023 12:52:55 +0200
Vladimir Oltean <vladimir.oltean@....com> wrote:

> > > 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.
> 
> 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/

Yes I am also following his patch series. 

> 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?

It does not support it for now.
I didn't want to base my work on his series as it could work without it for now
and I didn't want to wait to have his series accepted. It is more a future
possible support as I don't have anything to test it and I don't know if such
hardware exists right now.
I think it will be extensible to support that, my thinking was to create this
struct in net_device struct:

struct {
	enum layer;
	u32 id;
} ts;

With id saving the phy_index of the PHY X used when the layer PHY is selected.
This id could also be used to store the timestamp point in case of several
timestamp in a MAC.

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