From:   Vladimir Oltean <vladimir.oltean@nxp.com>
To:     Jakub Kicinski <kuba@kernel.org>
CC:     "netdev@vger.kernel.org" <netdev@vger.kernel.org>,
        Giuseppe Cavallaro <peppe.cavallaro@st.com>,
        Alexandre Torgue <alexandre.torgue@foss.st.com>,
        Jose Abreu <joabreu@synopsys.com>,
        "David S. Miller" <davem@davemloft.net>,
        Maxime Coquelin <mcoquelin.stm32@gmail.com>,
        "linux-stm32@st-md-mailman.stormreply.com" 
        <linux-stm32@st-md-mailman.stormreply.com>,
        "linux-arm-kernel@lists.infradead.org" 
        <linux-arm-kernel@lists.infradead.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Xiaoliang Yang <xiaoliang.yang_1@nxp.com>,
        Yannick Vignon <yannick.vignon@nxp.com>,
        Michael Olbrich <m.olbrich@pengutronix.de>,
        Ahmad Fatoum <a.fatoum@pengutronix.de>,
        Holger Assmann <h.assmann@pengutronix.de>,
        "kernel@pengutronix.de" <kernel@pengutronix.de>,
        Kurt Kanzenbach <kurt@linutronix.de>
Subject: Re: [PATCH net] net: stmmac: retain PTP clock time during
 SIOCSHWTSTAMP ioctls
Thread-Topic: [PATCH net] net: stmmac: retain PTP clock time during
 SIOCSHWTSTAMP ioctls
Thread-Index: AQHX3ZoAkTIcPNTQCUeJkFszF9TJdqwLyqeAgAJ5mYA=
Date:   Sun, 21 Nov 2021 17:46:36 +0000
Message-ID: <20211121174635.y7ljlas26xpgfp4j@skbuf>
References: <20211119230542.3402726-1-vladimir.oltean@nxp.com>
 <20211119195851.2181aab3@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com>
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On Fri, Nov 19, 2021 at 07:58:51PM -0800, Jakub Kicinski wrote:
> On Sat, 20 Nov 2021 01:05:42 +0200 Vladimir Oltean wrote:
> > Currently, when user space emits SIOCSHWTSTAMP ioctl calls such as
> > enabling/disabling timestamping or changing filter settings, the driver
> > reads the current CLOCK_REALTIME value and programming this into the
> > NIC's hardware clock. This might be necessary during system
> > initialization, but at runtime, when the PTP clock has already been
> > synchronized to a grandmaster, a reset of the timestamp settings might
> > result in a clock jump. Furthermore, if the clock is also controlled by
> > phc2sys in automatic mode (where the UTC offset is queried from ptp4l),
> > that UTC-to-TAI offset (currently 37 seconds in 2021) would be
> > temporarily reset to 0, and it would take a long time for phc2sys to
> > readjust so that CLOCK_REALTIME and the PHC are apart by 37 seconds
> > again.
> >=20
> > To address the issue, we introduce a new function called
> > stmmac_init_tstamp_counter(), which gets called during ndo_open().
> > It contains the code snippet moved from stmmac_hwtstamp_set() that
> > manages the time synchronization. Besides, the sub second increment
> > configuration is also moved here since the related values are hardware
> > dependent and runtime invariant.
> >=20
> > Furthermore, the hardware clock must be kept running even when no time
> > stamping mode is selected in order to retain the synchronized time base=
.
> > That way, timestamping can be enabled again at any time only with the
> > need to compensate the clock's natural drifting.
> >=20
> > As a side effect, this patch fixes the issue that ptp_clock_info::enabl=
e
> > can be called before SIOCSHWTSTAMP and the driver (which looks at
> > priv->systime_flags) was not prepared to handle that ordering.
>=20
> Makes build fail:
>=20
> ERROR: modpost: "stmmac_init_tstamp_counter" [drivers/net/ethernet/stmicr=
o/stmmac/stmmac-platform.ko] undefined!

You're right, I'm missing an EXPORT_SYMBOL, thanks.=