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Date:   Mon, 2 Oct 2023 17:29:58 -0700
Message-ID: <CAF2d9jgWpwNye89qrANfngG2+NQPDhpZQjXMKBDG6x7e32_cOw@mail.gmail.com>
Subject: Re: [PATCH 3/4] ptp: add ioctl interface for ptp_gettimex64any()
To:     Richard Cochran <richardcochran@gmail.com>
Cc:     Netdev <netdev@vger.kernel.org>,
        Linux <linux-kernel@vger.kernel.org>,
        David Miller <davem@davemloft.net>,
        Jakub Kicinski <kuba@kernel.org>,
        Eric Dumazet <edumazet@google.com>,
        Paolo Abeni <pabeni@redhat.com>,
        Jonathan Corbet <corbet@lwn.net>,
        Don Hatchett <hatch@google.com>,
        Yuliang Li <yuliangli@google.com>,
        Mahesh Bandewar <mahesh@bandewar.net>,
        Rahul Rameshbabu <rrameshbabu@nvidia.com>
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On Sat, Sep 30, 2023 at 2:25=E2=80=AFPM Richard Cochran
<richardcochran@gmail.com> wrote:
>
> On Thu, Sep 28, 2023 at 07:37:43PM -0700, Mahesh Bandewar wrote:
> > add an ioctl op PTP_SYS_OFFSET_ANY2 to support ptp_gettimex64any() meth=
od
>
> This is a useful idea.
>
> But how about a new system call instead?
>
>     clock_compare(clockid_t a, clockid_t b);
>
The purpose of this API is not to compare clocks but to get the width
of reading the MTS value (offered by NICs) in terms of the timebase
that is selected to essentially improve the accuracy.

> It would accept any two clock IDs.
>
> I've been wanting this for a long time, but never found time to
> implement it.
>
> Thanks,
> Richard