Re: [PATCH net-next v5 09/13] net: phylink: Use phy_caps_lookup for fixed-link configuration

["Russell King (Oracle)" <linux@armlinux.org.uk>]

On Thu, Mar 27, 2025 at 06:16:00PM -0700, Alexander H Duyck wrote:
> On Fri, 2025-03-07 at 18:36 +0100, Maxime Chevallier wrote:
> > When phylink creates a fixed-link configuration, it finds a matching
> > linkmode to set as the advertised, lp_advertising and supported modes
> > based on the speed and duplex of the fixed link.
> > 
> > Use the newly introduced phy_caps_lookup to get these modes instead of
> > phy_lookup_settings(). This has the side effect that the matched
> > settings and configured linkmodes may now contain several linkmodes (the
> > intersection of supported linkmodes from the phylink settings and the
> > linkmodes that match speed/duplex) instead of the one from
> > phy_lookup_settings().
> > 
> > Signed-off-by: Maxime Chevallier <maxime.chevallier@bootlin.com>
> > ---
> >  drivers/net/phy/phylink.c | 44 +++++++++++++++++++++++++++------------
> >  1 file changed, 31 insertions(+), 13 deletions(-)
> > 
> > diff --git a/drivers/net/phy/phylink.c b/drivers/net/phy/phylink.c
> > index cf9f019382ad..8e2b7d647a92 100644
> > --- a/drivers/net/phy/phylink.c
> > +++ b/drivers/net/phy/phylink.c
> > @@ -802,12 +802,26 @@ static int phylink_validate(struct phylink *pl, unsigned long *supported,
> >  	return phylink_validate_mac_and_pcs(pl, supported, state);
> >  }
> >  
> > +static void phylink_fill_fixedlink_supported(unsigned long *supported)
> > +{
> > +	linkmode_set_bit(ETHTOOL_LINK_MODE_10baseT_Half_BIT, supported);
> > +	linkmode_set_bit(ETHTOOL_LINK_MODE_10baseT_Full_BIT, supported);
> > +	linkmode_set_bit(ETHTOOL_LINK_MODE_100baseT_Half_BIT, supported);
> > +	linkmode_set_bit(ETHTOOL_LINK_MODE_100baseT_Full_BIT, supported);
> > +	linkmode_set_bit(ETHTOOL_LINK_MODE_1000baseT_Half_BIT, supported);
> > +	linkmode_set_bit(ETHTOOL_LINK_MODE_1000baseT_Full_BIT, supported);
> > +	linkmode_set_bit(ETHTOOL_LINK_MODE_2500baseT_Full_BIT, supported);
> > +	linkmode_set_bit(ETHTOOL_LINK_MODE_5000baseT_Full_BIT, supported);
> > +	linkmode_set_bit(ETHTOOL_LINK_MODE_10000baseT_Full_BIT, supported);
> > +}
> > +
> 
> Any chance we can go with a different route here than just locking
> fixed mode to being only for BaseT configurations?
> 
> I am currently working on getting the fbnic driver up and running and I
> am using fixed-link mode as a crutch until I can finish up enabling
> QSFP module support for phylink and this just knocked out the supported
> link modes as I was using 25CR, 50CR, 50CR2, and 100CR2.
> 
> Seems like this should really be something handled by some sort of
> validation function rather than just forcing all devices using fixed
> link to assume that they are BaseT. I know in our direct attached
> copper case we aren't running autoneg so that plan was to use fixed
> link until we can add more flexibility by getting QSFP support going.

Please look back at phylink's historical behaviour. Phylink used to
use phy_lookup_setting() to locate the linkmode for the speed and
duplex. That is the behaviour that we should be aiming to preserve.

We were getting:

speed	duplex	linkmode
10M	Half	10baseT_Half
10M	Full	10baseT_Full
100M	Half	100baseT_Half
100M	Full	100baseT_Full
1G	Half	1000baseT_Half
1G	Full	1000baseT_Full (this changed over time)
2.5G	Full	2500baseT_Full
5G	Full	5000baseT_Full

At this point, things get weird because of the way linkmodes were
added, as we return the _first_ match. Before commit 3c6b59d6f07c
("net: phy: Add more link modes to the settings table"):

10G	Full	10000baseKR_Full
Faster speeds not supported

After the commit:
10G	Full	10000baseCR_Full
20G	Full	20000baseKR2_Full
25G	Full	25000baseCR_Full
40G	Full	40000baseCR4_Full
50G	Full	50000baseCR2_Full
56G	Full	56000baseCR4_Full
100G	Full	100000baseCR4_Full

It's all a bit random. :(

-- 
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