RE: [PATCH net v5 1/3] net: phylink: add phylink_expects_phy() method

["Sit, Michael Wei Hong" <michael.wei.hong.sit@intel.com>]

> -----Original Message-----
> From: Maxime Chevallier <maxime.chevallier@bootlin.com>
> Sent: Wednesday, April 12, 2023 4:38 PM
> To: Sit, Michael Wei Hong <michael.wei.hong.sit@intel.com>
> Cc: Giuseppe Cavallaro <peppe.cavallaro@st.com>; Alexandre
> Torgue <alexandre.torgue@foss.st.com>; Jose Abreu
> <joabreu@synopsys.com>; David S . Miller <davem@davemloft.net>;
> Eric Dumazet <edumazet@google.com>; Jakub Kicinski
> <kuba@kernel.org>; Paolo Abeni <pabeni@redhat.com>; Maxime
> Coquelin <mcoquelin.stm32@gmail.com>; Ong, Boon Leong
> <boon.leong.ong@intel.com>; netdev@vger.kernel.org; linux-
> stm32@st-md-mailman.stormreply.com; linux-arm-
> kernel@lists.infradead.org; linux-kernel@vger.kernel.org;
> linux@armlinux.org.uk; hkallweit1@gmail.com; andrew@lunn.ch;
> Looi, Hong Aun <hong.aun.looi@intel.com>; Voon, Weifeng
> <weifeng.voon@intel.com>; Lai, Peter Jun Ann
> <peter.jun.ann.lai@intel.com>; alexis.lothore@bootlin.com
> Subject: Re: [PATCH net v5 1/3] net: phylink: add
> phylink_expects_phy() method
> 
> Hello everyone,
> 
> On Thu, 30 Mar 2023 17:14:02 +0800
> Michael Sit Wei Hong <michael.wei.hong.sit@intel.com> wrote:
> 
> > Provide phylink_expects_phy() to allow MAC drivers to check if it is
> > expecting a PHY to attach to. Since fixed-linked setups do not need
> to
> > attach to a PHY.
> >
> > Provides a boolean value as to if the MAC should expect a PHY.
> > Returns true if a PHY is expected.
> 
> I'm currently working on the TSE rework for dwmac_socfpga, and I
> noticed one regression since this patch, when using an SFP, see
> details below :
> 
> > Reviewed-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
> > Signed-off-by: Michael Sit Wei Hong
> <michael.wei.hong.sit@intel.com>
> > ---
> >  drivers/net/phy/phylink.c | 19 +++++++++++++++++++
> >  include/linux/phylink.h   |  1 +
> >  2 files changed, 20 insertions(+)
> >
> > diff --git a/drivers/net/phy/phylink.c b/drivers/net/phy/phylink.c
> > index 1a2f074685fa..30c166b33468 100644
> > --- a/drivers/net/phy/phylink.c
> > +++ b/drivers/net/phy/phylink.c
> > @@ -1586,6 +1586,25 @@ void phylink_destroy(struct phylink
> *pl)  }
> > EXPORT_SYMBOL_GPL(phylink_destroy);
> >
> > +/**
> > + * phylink_expects_phy() - Determine if phylink expects a phy to
> be
> > attached
> > + * @pl: a pointer to a &struct phylink returned from
> phylink_create()
> > + *
> > + * When using fixed-link mode, or in-band mode with 1000base-X
> or
> > 2500base-X,
> > + * no PHY is needed.
> > + *
> > + * Returns true if phylink will be expecting a PHY.
> > + */
> > +bool phylink_expects_phy(struct phylink *pl) {
> > +	if (pl->cfg_link_an_mode == MLO_AN_FIXED ||
> > +	    (pl->cfg_link_an_mode == MLO_AN_INBAND &&
> > +	     phy_interface_mode_is_8023z(pl->link_config.interface)))
> 
> From the discussion, at one point Russell mentionned [1] :
> "If there's a sfp bus, then we don't expect a PHY from the MAC
> driver (as there can only be one PHY attached), and as
> phylink_expects_phy() is for the MAC driver to use, we should be
> returning false if
> pl->sfp_bus != NULL."
> 
> This makes sense and indeed adding the relevant check solves the
> issue.
> 
> Am I correct in assuming this was an unintentional omission from
> this patch, or was the pl->sfp_bus check dropped on purpose ?
> 
> > +		return false;
> > +	return true;
> > +}
> > +EXPORT_SYMBOL_GPL(phylink_expects_phy);
> 
> Thanks,
> 
> Maxime
> 

Russell also did mention:
" The reason for the extra "&& !pl->sfp_bus" in phylink_attach_phy()
is to allow SFPs to connect to the MAC using inband mode with
1000base-X and 2500base-X interface modes. These are not for the
MAC-side of things though."

So I thought that the check can be dropped. I do not have any SFP hardware
to test, if adding the check make sense, you can send us a patch so we can
test it out.
> [1] :
> https://lore.kernel.org/netdev/ZCQJWcdfmualIjvX@shell.armlinux.o
> rg.uk/