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

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Message-ID: <20231122085459.1601141e@kernel.org>
Date:   Wed, 22 Nov 2023 08:54:59 -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 16:36:18 +0200 Vladimir Oltean wrote:
> @Jakub, for your long-term "MAC timestamps for PTP, DMA for everything else".
> How do you see this? I guess we need some sort of priority function in
> the UAPI between hwtstamp providers.
> 
> And even with that, I think the enums that we currently have for filters
> are not specific enough. The most we could expose is:
> 
>                       MAC provider                      DMA provider
> 
> hwtstamp_rx_filters   HWTSTAMP_FILTER_PTP_V2_EVENT      HWTSTAMP_FILTER_ALL
> tx_type               HWTSTAMP_TX_ON                    HWTSTAMP_TX_ON
> 
> but it isn't clear: for PTP, does the DMA provider give you an RX
> timestamp too?

If we phrase it as "precise / approximate" rather than "MAC / DMA" - it
seems fairly intuitive to give the best timestamp available for a given
packet, no?

> What about a TX timestamp?

I was thinking - socket flag to make packets for a given socket request
precise timestamps.