linux-kernel - RE: [PATCH net-next 6/6 v2] net: dsa: microchip: Setup fiber ports for KSZ8463

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Message-ID:
 <DM3PR11MB8736DE8A01523BD67AF73766EC4EA@DM3PR11MB8736.namprd11.prod.outlook.com>
Date: Tue, 8 Jul 2025 19:45:44 +0000
From: <Tristram.Ha@...rochip.com>
To: <maxime.chevallier@...tlin.com>
CC: <Woojung.Huh@...rochip.com>, <andrew@...n.ch>, <olteanv@...il.com>,
	<robh@...nel.org>, <krzk+dt@...nel.org>, <conor+dt@...nel.org>,
	<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 6/6 v2] net: dsa: microchip: Setup fiber ports
 for KSZ8463

> Hi Tristram,
> 
> On Mon, 7 Jul 2025 20:16:48 -0700
> <Tristram.Ha@...rochip.com> wrote:
> 
> > From: Tristram Ha <tristram.ha@...rochip.com>
> >
> > The fiber ports in KSZ8463 cannot be detected internally, so it requires
> > specifying that condition in the device tree.  Like the one used in
> > Micrel PHY the port link can only be read and there is no write to the
> > PHY.  The driver programs registers to operate fiber ports correctly.
> >
> > The PTP function of the switch is also turned off as it may interfere the
> > normal operation of the MAC.
> >
> > Signed-off-by: Tristram Ha <tristram.ha@...rochip.com>
> > ---
> >  drivers/net/dsa/microchip/ksz8.c       | 26 ++++++++++++++++++++++++++
> >  drivers/net/dsa/microchip/ksz_common.c |  3 +++
> >  2 files changed, 29 insertions(+)
> >
> > diff --git a/drivers/net/dsa/microchip/ksz8.c b/drivers/net/dsa/microchip/ksz8.c
> > index 904db68e11f3..1207879ef80c 100644
> > --- a/drivers/net/dsa/microchip/ksz8.c
> > +++ b/drivers/net/dsa/microchip/ksz8.c
> > @@ -1715,6 +1715,7 @@ void ksz8_config_cpu_port(struct dsa_switch *ds)
> >       const u32 *masks;
> >       const u16 *regs;
> >       u8 remote;
> > +     u8 fiber_ports = 0;
> >       int i;
> >
> >       masks = dev->info->masks;
> > @@ -1745,6 +1746,31 @@ void ksz8_config_cpu_port(struct dsa_switch *ds)
> >               else
> >                       ksz_port_cfg(dev, i, regs[P_STP_CTRL],
> >                                    PORT_FORCE_FLOW_CTRL, false);
> > +             if (p->fiber)
> > +                     fiber_ports |= (1 << i);
> > +     }
> > +     if (ksz_is_ksz8463(dev)) {
> > +             /* Setup fiber ports. */
> 
> What does fiber port mean ? Is it 100BaseFX ? As this configuration is
> done only for the CPU port (it seems), looks like this mode is planned
> to be used as the MAC to MAC mode on the DSA conduit. So, instead of
> using this property maybe you should implement that as handling the
> "100base-x" phy-mode ?
> 
> > +             if (fiber_ports) {
> > +                     regmap_update_bits(ksz_regmap_16(dev),
> > +                                        reg16(dev, KSZ8463_REG_CFG_CTRL),
> > +                                        fiber_ports << PORT_COPPER_MODE_S,
> > +                                        0);
> > +                     regmap_update_bits(ksz_regmap_16(dev),
> > +                                        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);
> >       }
> >  }
> >
> > diff --git a/drivers/net/dsa/microchip/ksz_common.c
> b/drivers/net/dsa/microchip/ksz_common.c
> > index c08e6578a0df..b3153b45ced9 100644
> > --- a/drivers/net/dsa/microchip/ksz_common.c
> > +++ b/drivers/net/dsa/microchip/ksz_common.c
> > @@ -5441,6 +5441,9 @@ int ksz_switch_register(struct ksz_device *dev)
> >                                               &dev->ports[port_num].interface);
> >
> >                               ksz_parse_rgmii_delay(dev, port_num, port);
> > +                             dev->ports[port_num].fiber =
> > +                                     of_property_read_bool(port,
> > +                                                           "micrel,fiber-mode");
> 
> Shouldn't this be described in the binding ?
> 
> >                       }
> >                       of_node_put(ports);
> >               }

The "micrel,fiber-mode" is described in Documentation/devicetree/
bindings/net/micrel.txt.

Some old KSZ88XX switches have option of using fiber in a port running
100base-fx.  Typically they have a register indicating that configuration
and the driver just treats the port as having a PHY and reads the link
status and speed as normal except there is no write to those PHY related
registers.  KSZ8463 does not have that option so the driver needs to be
told.