netdev - Re: [PATCH v2 4/9] mlxsw: spectrum_ptp: Use generic helper function

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Message-ID: <20200729134958.GC23222@hoboy>
Date:   Wed, 29 Jul 2020 06:49:58 -0700
From:   Richard Cochran <richardcochran@...il.com>
To:     Kurt Kanzenbach <kurt@...utronix.de>
Cc:     Russell King - ARM Linux admin <linux@...linux.org.uk>,
        Petr Machata <petrm@...lanox.com>,
        Andrew Lunn <andrew@...n.ch>,
        Vivien Didelot <vivien.didelot@...il.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Jiri Pirko <jiri@...lanox.com>,
        Ido Schimmel <idosch@...lanox.com>,
        Heiner Kallweit <hkallweit1@...il.com>,
        Grygorii Strashko <grygorii.strashko@...com>,
        Ivan Khoronzhuk <ivan.khoronzhuk@...aro.org>,
        Samuel Zou <zou_wei@...wei.com>, netdev@...r.kernel.org
Subject: Re: [PATCH v2 4/9] mlxsw: spectrum_ptp: Use generic helper function

On Wed, Jul 29, 2020 at 12:29:08PM +0200, Kurt Kanzenbach wrote:

> I'll test it and send v3. But before, I've got another question that
> somebody might have an answer to:
> 
> The ptp v1 code always does locate the message type at
> 
>  msgtype = data + offset + OFF_PTP_CONTROL
> 
> OFF_PTP_CONTROL is 32. However, looking at the ptp v1 header, the
> message type is located at offset 20. What am I missing here?


My source back in the day was the John Eidson book.  In Appendix A it claims


                   Table A.1. Common PTP message fields

   Field name                    Purpose
   --------------------------------------------------------------------
   messageType                   Identifies message as event or general
   control                       Indicates the message type, e.g., Sync


So I think the code is correct.

Thanks,
Richard