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

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Date:   Wed, 29 Nov 2023 16:06:38 -0800
From:   Rahul Rameshbabu <rrameshbabu@...dia.com>
To:     Jakub Kicinski <kuba@...nel.org>
Cc:     Köry Maincent <kory.maincent@...tlin.com>,
        Vladimir Oltean <vladimir.oltean@....com>,
        Andrew Lunn <andrew@...n.ch>,
        Florian Fainelli <florian.fainelli@...adcom.com>,
        Broadcom internal kernel review list 
        <bcm-kernel-feedback-list@...adcom.com>,
        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, 29 Nov, 2023 15:56:13 -0800 Jakub Kicinski <kuba@...nel.org> wrote:
> On Wed, 29 Nov 2023 23:00:34 +0100 Köry Maincent wrote:
>> > Not sure why you say "not used", though. Are you not planning to expose
>> > the qualifier as an attribute to the listing of hwtstamp providers
>> > offered to user space by ETHTOOL_MSG_TSINFO_GET?  
>> 
>> Yes I will, I was just saying that all the PHC would be set as precise for now.
>> Approximate timestamp quality won't be used because IIUC there are no NIC driver
>> supporting it yet.
>
> Agreed that we should add the attr from the start.
>
> Maybe we can ask/work with Rahul <rrameshbabu@...dia.com>
> to implement the right thing in mlx5?

Thanks for looping me in. We were already looking at this patch series
out of interest. I saw your suggestion to rephrase "MAC / DMA" as
"precise / approximate", which we really like for mlx5 devices because
our "approximate" timestamping logic is not exactly a "MAC" timestamp
but its not a port timestamp that has the greater precision we use. I
have a task already for implementing support for this ethtool attribute.
If folks here are open to it, I can add mlx5 support for both modes in
this patch series for the next revision that will entail the discussed
changes.

>
> Failing that we can mark mlx5 as imprecise, until its sorted out.
> So that we have both types in the tree.

--
Thanks,

Rahul Rameshbabu