linux-kernel - Re: [PATCH net-next v5 08/16] net: ethtool: Add a command to expose current time stamping layer

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Message-ID: <20231013161446.st7tlemyaj3ggkgk@skbuf>
Date:   Fri, 13 Oct 2023 19:14:46 +0300
From:   Vladimir Oltean <vladimir.oltean@....com>
To:     Jakub Kicinski <kuba@...nel.org>
Cc:     Köry Maincent <kory.maincent@...tlin.com>,
        Florian Fainelli <florian.fainelli@...adcom.com>,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-doc@...r.kernel.org,
        Thomas Petazzoni <thomas.petazzoni@...tlin.com>,
        "David S . Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Paolo Abeni <pabeni@...hat.com>,
        Jonathan Corbet <corbet@....net>,
        Jay Vosburgh <j.vosburgh@...il.com>,
        Andy Gospodarek <andy@...yhouse.net>,
        Nicolas Ferre <nicolas.ferre@...rochip.com>,
        Claudiu Beznea <claudiu.beznea@...on.dev>,
        Horatiu Vultur <horatiu.vultur@...rochip.com>,
        UNGLinuxDriver@...rochip.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>,
        Richard Cochran <richardcochran@...il.com>,
        Radu Pirea <radu-nicolae.pirea@....nxp.com>,
        Willem de Bruijn <willemdebruijn.kernel@...il.com>,
        Michael Walle <michael@...le.cc>,
        Jacob Keller <jacob.e.keller@...el.com>,
        Maxime Chevallier <maxime.chevallier@...tlin.com>
Subject: Re: [PATCH net-next v5 08/16] net: ethtool: Add a command to expose
 current time stamping layer

On Fri, Oct 13, 2023 at 09:00:20AM -0700, Jakub Kicinski wrote:
> On Tue, 10 Oct 2023 10:23:43 +0200 Köry Maincent wrote:
> > > Why do we have to set NETDEV_TIMESTAMPING here, or is this a round-about 
> > > way of enumerating 0, 1, 2 and 3?  
> > 
> > I answered you above the software timestamping should have the
> > NETDEV_TIMESTAMPING bit set as it is done from the net device driver.
> > 
> > What I was thinking is that all the new timestamping should have
> > NETDEV_TIMESTAMPING or PHYLIB_TIMESTAMPING set to know which API to pass
> > through.
> > Like we could add these in the future:
> > MAC_DMA_TIMESTAMPING = (2 << 2) | (1 >> 0),
> > MAC_PRECISION_TIMESTAMPING = (3 << 2) | (1 >> 0),
> > ...
> > PHY_SFP_TIMESTAMPING = (2 << 2) | (1 << 1),
> > ...
> 
> What is "PRECISION"? DMA is a separate block like MAC and PHY.

If DMA is a separate block like MAC and PHY, can it have its own PHC
device, and the ethtool UAPI only lists the timestamping-capable PHCs
for one NIC, and is able to select between them? Translation between the
UAPI-visible PHC index and MAC, DMA, phylib PHY, other PHY etc can then
be done by the kernel as needed.