linux-kernel - Re: [PATCH net-next RFC 8/9] net: dsa: mv88e6xxx: add rx/tx timestamping support

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Message-ID: <20171008151228.h75zo7wmkqvocixs@localhost>
Date:   Sun, 8 Oct 2017 11:12:29 -0400
From:   Richard Cochran <richardcochran@...il.com>
To:     Brandon Streiff <brandon.streiff@...com>
Cc:     netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        "David S. Miller" <davem@...emloft.net>,
        Florian Fainelli <f.fainelli@...il.com>,
        Andrew Lunn <andrew@...n.ch>,
        Vivien Didelot <vivien.didelot@...oirfairelinux.com>,
        Erik Hons <erik.hons@...com>
Subject: Re: [PATCH net-next RFC 8/9] net: dsa: mv88e6xxx: add rx/tx
 timestamping support

On Thu, Sep 28, 2017 at 10:25:40AM -0500, Brandon Streiff wrote:
> We also utilize a feature of the "generation 3" PTP hardware that lets
> us to embed the timestamp value into one of the reserved fields in the
> PTP header. This lets us extract the timestamp out of the header and
> avoid an SMI access in the RX codepath. (This implementation does not
> presently support the older generations.)

That is fine for the later models, but we really need the code to read
over MDIO as well.  You added .ptp_support = true for those older
switches, and so the present series won't work.

If it helps, maybe I can adapt the relevant code from my driver to
your work.

Thanks,
Richard