linux-kernel - Re: [PATCH 7/7] net: dsa: b53: Expose PTP timestamping ioctls to userspace

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Message-ID: <CA+h21hq=6eMrCJ=TS+zdrxHhuxcmVFLU0hzGmhLXUGFU-vLhPg@mail.gmail.com>
Date:   Fri, 26 Nov 2021 18:42:57 +0200
From:   Vladimir Oltean <olteanv@...il.com>
To:     Richard Cochran <richardcochran@...il.com>
Cc:     Kurt Kanzenbach <kurt@...utronix.de>,
        Martin Kaistra <martin.kaistra@...utronix.de>,
        Florian Fainelli <f.fainelli@...il.com>,
        Andrew Lunn <andrew@...n.ch>,
        Vivien Didelot <vivien.didelot@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        John Stultz <john.stultz@...aro.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Stephen Boyd <sboyd@...nel.org>,
        Russell King <linux@...linux.org.uk>,
        Marc Kleine-Budde <mkl@...gutronix.de>,
        linux-kernel@...r.kernel.org, netdev@...r.kernel.org
Subject: Re: [PATCH 7/7] net: dsa: b53: Expose PTP timestamping ioctls to userspace

On Fri, 26 Nov 2021 at 18:31, Richard Cochran <richardcochran@...il.com> wrote:
>
> On Fri, Nov 26, 2021 at 09:42:32AM +0100, Kurt Kanzenbach wrote:
> > On Thu Nov 25 2021, Vladimir Oltean wrote:
> > > Richard, when the request is PTP_V2_EVENT and the response is
> > > PTP_V2_L2_EVENT, is that an upgrade or a downgrade?
> >
> > It is a downgrade, isn't it?
>
> Yes.  "Any kind of PTP Event" is a superset of "Any Layer-2 Event".
>
> When userland asks for "any kind", then it wants to run PTP over IPv4,
> IPv6, or Layer2, maybe even more than one at the same time.  If the
> driver changes that to Layer2 only, then the PTP possibilities have
> been downgraded.

Well, when I said that it's essentially the same pattern, this is what
I was talking about. The b53 driver downgrades everything and the
kitchen sink to HWTSTAMP_FILTER_PTP_V2_L2_EVENT, the ocelot driver to
HWTSTAMP_FILTER_PTP_V2_EVENT, and both are buggy for the same reason.
I don't see why you mention that there is an important difference
between HWTSTAMP_FILTER_PTP_V2_L2_EVENT and
HWTSTAMP_FILTER_PTP_V2_EVENT. I know there is, but the _pattern_ is
the same.
I'm still missing something obvious, aren't I?