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

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Date: Tue, 21 Nov 2023 18:31:14 +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 Tue, 21 Nov 2023 00:05:49 +0200
Vladimir Oltean <vladimir.oltean@....com> wrote:

> On Mon, Nov 20, 2023 at 01:37:37PM -0800, Jakub Kicinski wrote:
> > > Is it an accurate summary?  
> > 
> > Yes.
> > 
> > For now we can impose the requirement that only one can be active 
> > easily at the kernel level. But the uAPI should allow expressing more.  
> 
> I see. That's quite something to think about for Köry. In its defense,
> I also agree that this idea seems the most orthogonal to everything else
> that we have or may want to add in the future, and is not likely to
> become obsoleted by some other mechanism that can achieve the same
> thing, but in a more flexible way. It's just that it's quite the task.
> 
> I sense it may be time to dust off and submit the rest of my
> ndo_hwtstamp_get()/ ndo_hwtstamp_set() conversions before a netlink
> conversion of SIOCGHWTSTAMP/SIOCSHWTSTAMP could even take place...
> https://github.com/vladimiroltean/linux/commits/ndo-hwtstamp-v9

Ok I kind of got an idea of what is your prerequisites.

If I summarize, a solution could be this:

- Expand struct hwtstamp_config with a phc_index member for the SIOCG/SHWTSTAMP
  commands.
  To keep backward compatibility if phc_index is not set in the hwtstamp_config
  data from userspace use the default hwtstamp (the default being selected as
  done in my patch series).
  Is this possible, would it breaks things?

- In netlink part, send one netlink tsinfo skb for each phc_index.

Could be done in a later patch series:
- Expand netlink TSINFO with ETHTOOL_A_TSINFO_HWSTAMP_PROVIDER_QUALIFIER.
  Describing this struct:
enum ethtool_hwstamp_provider_qualifier {
 	ETHTOOL_HWSTAMP_PROVIDER_QUALIFIER_PRECISE,
 	ETHTOOL_HWSTAMP_PROVIDER_QUALIFIER_APPROX,
}; 

  Set the desired qualifier through TSINFO_SET or through SIOCSHWTSTAMP by
  expanding again the struct hwtstamp_config.

Do you think this is feasible?
I might miss some core stuff.

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