netdev - Re: [PATCH 1/5] net: fec: properly support external PTP PHY for hardware time stamping

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20200708110053.GC9080@hoboy>
Date:   Wed, 8 Jul 2020 04:00:53 -0700
From:   Richard Cochran <richardcochran@...il.com>
To:     Vladimir Oltean <olteanv@...il.com>
Cc:     Sergey Organov <sorganov@...il.com>, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, Fugang Duan <fugang.duan@....com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>, andrew@...n.ch
Subject: Re: [PATCH  1/5] net: fec: properly support external PTP PHY for
 hardware time stamping

On Tue, Jul 07, 2020 at 10:04:37AM +0300, Vladimir Oltean wrote:
> > > We do it like this:
> > > - DSA: If there is a timestamping switch stacked on top of a
> > >   timestamping Ethernet MAC, the switch hijacks the .ndo_do_ioctl of the
> > >   host port, and you are supposed to use the PTP clock of the switch,
> > >   through the .ndo_do_ioctl of its own (virtual) net devices. This
> > >   approach works without changing any code in each individual Ethernet
> > >   MAC driver.
> > > - PHY: The Ethernet MAC driver needs to be kind enough to check whether
> > >   the PHY supports hw timestamping, and pass this ioctl to that PHY
> > >   while making sure it doesn't do anything stupid in the meanwhile, like
> > >   also acting upon that timestamping request itself.
> > >
> > > Both are finicky in their own ways. There is no real way for the user to
> > > select which PHC they want to use. The assumption is that you'd always
> > > want to use the outermost one, and that things in the kernel side always
> > > collaborate towards that end.

Vladimir, your explanations in this thread are valuable.  Please
consider converting them into a patch to expand

   Documentation/networking/timestamping.rst


Thanks,
Richard