netdev - Re: [RFC PATCH 0/2] AT8031 PHY timestamping support

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Message-ID: <20200226025441.GB10271@localhost>
Date:   Tue, 25 Feb 2020 18:54:41 -0800
From:   Richard Cochran <richardcochran@...il.com>
To:     Michael Walle <michael@...le.cc>
Cc:     Andrew Lunn <andrew@...n.ch>, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Florian Fainelli <f.fainelli@...il.com>,
        Heiner Kallweit <hkallweit1@...il.com>,
        Russell King <linux@...linux.org.uk>,
        "David S . Miller" <davem@...emloft.net>
Subject: Re: [RFC PATCH 0/2] AT8031 PHY timestamping support

On Wed, Feb 26, 2020 at 01:07:26AM +0100, Michael Walle wrote:
> Am 26. Februar 2020 00:50:40 MEZ schrieb Andrew Lunn <andrew@...n.ch>:
> >That sounds fundamentally broken.

Right.  It can't work unless the PHY latches the time stamp.

> This might be the case, but the datasheet (some older revision can
> be found on the internet, maybe you find something) doesn't mention
> it. Nor does the PTP "guide" (I don't know the exact name, I'd have
> to check at work) of this PHY. Besides the timestamp there's also
> the sequence number and the source port id which would need to be
> read atomically together with the timestamp.

Maybe the part is not intended to be used at all in this way?

AFAICT, PHYs like this are meant to feed a "PTP frame detected" pulse
into the time stamping unit on the attached MAC.  The interrupt serves
to allow the SW to gather the matching fields from the frame.

Thanks,
Richard