linux-kernel - RE: [PATCH net-next v3 7/7] net: dsa: microchip: Disable PTP function of KSZ8463

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Message-ID:
 <LV3PR11MB874269079536CDB53183760DEC49A@LV3PR11MB8742.namprd11.prod.outlook.com>
Date: Wed, 9 Jul 2025 22:59:58 +0000
From: <Tristram.Ha@...rochip.com>
To: <olteanv@...il.com>
CC: <Woojung.Huh@...rochip.com>, <andrew@...n.ch>, <robh@...nel.org>,
	<krzk+dt@...nel.org>, <conor+dt@...nel.org>, <maxime.chevallier@...tlin.com>,
	<davem@...emloft.net>, <edumazet@...gle.com>, <kuba@...nel.org>,
	<pabeni@...hat.com>, <marex@...x.de>, <UNGLinuxDriver@...rochip.com>,
	<devicetree@...r.kernel.org>, <netdev@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>
Subject: RE: [PATCH net-next v3 7/7] net: dsa: microchip: Disable PTP function
 of KSZ8463

> On Tue, Jul 08, 2025 at 05:32:33PM -0700, Tristram.Ha@...rochip.com wrote:
> > From: Tristram Ha <tristram.ha@...rochip.com>
> >
> > The PTP function of KSZ8463 is on by default.  However, its proprietary
> > way of storing timestamp directly in a reserved field inside the PTP
> > message header is not suitable for use with the current Linux PTP stack
> > implementation.  It is necessary to disable the PTP function to not
> > interfere the normal operation of the MAC.
> >
> > Signed-off-by: Tristram Ha <tristram.ha@...rochip.com>
> > ---
> >  drivers/net/dsa/microchip/ksz8.c | 11 +++++++++++
> >  1 file changed, 11 insertions(+)
> >
> > diff --git a/drivers/net/dsa/microchip/ksz8.c b/drivers/net/dsa/microchip/ksz8.c
> > index ddbd05c44ce5..fd4a000487d6 100644
> > --- a/drivers/net/dsa/microchip/ksz8.c
> > +++ b/drivers/net/dsa/microchip/ksz8.c
> > @@ -1761,6 +1761,17 @@ void ksz8_config_cpu_port(struct dsa_switch *ds)
> >                                          reg16(dev, KSZ8463_REG_DSP_CTRL_6),
> >                                          COPPER_RECEIVE_ADJUSTMENT, 0);
> >               }
> > +
> > +             /* Turn off PTP function as the switch's proprietary way of
> > +              * handling timestamp is not supported in current Linux PTP
> > +              * stack implementation.
> > +              */
> > +             regmap_update_bits(ksz_regmap_16(dev),
> > +                                reg16(dev, KSZ8463_PTP_MSG_CONF1),
> > +                                PTP_ENABLE, 0);
> > +             regmap_update_bits(ksz_regmap_16(dev),
> > +                                reg16(dev, KSZ8463_PTP_CLK_CTRL),
> > +                                PTP_CLK_ENABLE, 0);
> >       }
> >  }
> >
> > --
> > 2.34.1
> >
> 
> What prevents the user from later enabling this through
> ksz_set_hwtstamp_config(HWTSTAMP_TX_ONESTEP_P2P)?

The PTP engine in KSZ8463 is first generation.  The DSA PTP driver used
by KSZ9477 and LAN937X is for second generation, which uses tail tag to
pass along receive/transmit timestamp and port information.

It is not likely the PTP driver will be updated to support KSZ8463.
Currently that driver code is not activated except for KSZ9477 and
LAN937X.