netdev - RE: [PATCH net-next 3/3] net: ethernet: renesas: rswitch: Add phy_power

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Date:   Fri, 6 Jan 2023 07:34:38 +0000
From:   Yoshihiro Shimoda <yoshihiro.shimoda.uh@...esas.com>
To:     Russell King <linux@...linux.org.uk>
CC:     "andrew@...n.ch" <andrew@...n.ch>,
        "hkallweit1@...il.com" <hkallweit1@...il.com>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "edumazet@...gle.com" <edumazet@...gle.com>,
        "kuba@...nel.org" <kuba@...nel.org>,
        "pabeni@...hat.com" <pabeni@...hat.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-renesas-soc@...r.kernel.org" 
        <linux-renesas-soc@...r.kernel.org>
Subject: RE: [PATCH net-next 3/3] net: ethernet: renesas: rswitch: Add
 phy_power_{on,off}() calling

Hello Russell,

> From: Russell King, Sent: Tuesday, January 3, 2023 6:56 PM
> 
> On Mon, Dec 26, 2022 at 04:14:25PM +0900, Yoshihiro Shimoda wrote:
> > Some Ethernet PHYs (like marvell10g) will decide the host interface
> > mode by the media-side speed. So, the rswitch driver needs to
> > initialize one of the Ethernet SERDES (r8a779f0-eth-serdes) ports
> > after linked the Ethernet PHY up. The r8a779f0-eth-serdes driver has
> > .init() for initializing all ports and .power_on() for initializing
> > each port. So, add phy_power_{on,off} calling for it.
> >
> > Signed-off-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@...esas.com>
> > ---
> >  drivers/net/ethernet/renesas/rswitch.c | 8 ++++++++
> >  1 file changed, 8 insertions(+)
> >
> > diff --git a/drivers/net/ethernet/renesas/rswitch.c b/drivers/net/ethernet/renesas/rswitch.c
> > index ca79ee168206..2f335c95f5a8 100644
> > --- a/drivers/net/ethernet/renesas/rswitch.c
> > +++ b/drivers/net/ethernet/renesas/rswitch.c
> > @@ -1180,6 +1180,10 @@ static void rswitch_mac_link_down(struct phylink_config *config,
> >  				  unsigned int mode,
> >  				  phy_interface_t interface)
> >  {
> > +	struct net_device *ndev = to_net_dev(config->dev);
> > +	struct rswitch_device *rdev = netdev_priv(ndev);
> > +
> > +	phy_power_off(rdev->serdes);
> >  }
> >
> >  static void rswitch_mac_link_up(struct phylink_config *config,
> > @@ -1187,7 +1191,11 @@ static void rswitch_mac_link_up(struct phylink_config *config,
> >  				phy_interface_t interface, int speed,
> >  				int duplex, bool tx_pause, bool rx_pause)
> >  {
> > +	struct net_device *ndev = to_net_dev(config->dev);
> > +	struct rswitch_device *rdev = netdev_priv(ndev);
> > +
> >  	/* Current hardware cannot change speed at runtime */
> > +	phy_power_on(rdev->serdes);
> >  }
> >
> >  static const struct phylink_mac_ops rswitch_phylink_ops = {
> 
> This looks to me like it will break anyone using an in-band link,
> where the link status comes from the PCS behind the series that
> you're now powering down and up.

Thank you for your review!
To be honest, I didn't know about "an in-band link". So, I studied a little,
and then I might understand about your comments. However, I still don't
understand whether this hardware (rswitch) can support the "in-band link" or not.
This seems to need a special hardware feature for "in-band link" and
only software cannot support it, IIUC.
# Unfortunately, this hardware's datasheet cannot be in public for now though...

Anyway, I'll add a condition which this driver cannot support MLO_AN_INBAND
to avoid a problem by someone for now.

Best regards,
Yoshihiro Shimoda