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Message-ID: <Z-6hcQGI8tgshtMP@shell.armlinux.org.uk>
Date: Thu, 3 Apr 2025 15:55:45 +0100
From: "Russell King (Oracle)" <linux@...linux.org.uk>
To: Alexander Duyck <alexander.duyck@...il.com>
Cc: netdev@...r.kernel.org, andrew@...n.ch, hkallweit1@...il.com,
davem@...emloft.net, kuba@...nel.org, pabeni@...hat.com,
maxime.chevallier@...tlin.com
Subject: Re: [net PATCH 1/2] net: phy: Cleanup handling of recent changes to
phy_lookup_setting
On Tue, Apr 01, 2025 at 02:30:06PM -0700, Alexander Duyck wrote:
> From: Alexander Duyck <alexanderduyck@...com>
>
> The blamed commit introduced an issue where it was limiting the link
> configuration so that we couldn't use fixed-link mode for any settings
> other than twisted pair modes 10G or less. As a result this was causing the
> driver to lose any advertised/lp_advertised/supported modes when setup as a
> fixed link.
>
> To correct this we can add a check to identify if the user is in fact
> enabling a TP mode and then apply the mask to select only 1 of each speed
> for twisted pair instead of applying this before we know the number of bits
> set.
>
> Fixes: de7d3f87be3c ("net: phylink: Use phy_caps_lookup for fixed-link configuration")
> Signed-off-by: Alexander Duyck <alexanderduyck@...com>
> ---
> drivers/net/phy/phylink.c | 15 +++++++++++----
> 1 file changed, 11 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/net/phy/phylink.c b/drivers/net/phy/phylink.c
> index 16a1f31f0091..380e51c5bdaa 100644
> --- a/drivers/net/phy/phylink.c
> +++ b/drivers/net/phy/phylink.c
> @@ -713,17 +713,24 @@ static int phylink_parse_fixedlink(struct phylink *pl,
> phylink_warn(pl, "fixed link specifies half duplex for %dMbps link?\n",
> pl->link_config.speed);
>
> - linkmode_zero(pl->supported);
> - phylink_fill_fixedlink_supported(pl->supported);
> -
> + linkmode_fill(pl->supported);
> linkmode_copy(pl->link_config.advertising, pl->supported);
> phylink_validate(pl, pl->supported, &pl->link_config);
>
> c = phy_caps_lookup(pl->link_config.speed, pl->link_config.duplex,
> pl->supported, true);
> - if (c)
> + if (c) {
> linkmode_and(match, pl->supported, c->linkmodes);
>
> + /* Compatbility with the legacy behaviour:
> + * Report one single BaseT mode.
> + */
> + phylink_fill_fixedlink_supported(mask);
> + if (linkmode_intersects(match, mask))
> + linkmode_and(match, match, mask);
> + linkmode_zero(mask);
> + }
> +
I'm still wondering about the wiseness of exposing more than one link
mode for something that's supposed to be fixed-link.
For gigabit fixed links, even if we have:
phy-mode = "1000base-x";
speed = <1000>;
full-duplex;
in DT, we still state to ethtool:
Supported link modes: 1000baseT/Full
Advertised link modes: 1000baseT/Full
Link partner advertised link modes: 1000baseT/Full
Link partner advertised auto-negotiation: No
Speed: 1000Mb/s
Duplex: Full
Auto-negotiation: on
despite it being a 1000base-X link. This is perfectly reasonable,
because of the origins of fixed-links - these existed as a software
emulated baseT PHY no matter what the underlying link was.
So, is getting the right link mode for the underlying link important
for fixed-links? I don't think it is. Does it make sense to publish
multiple link modes for a fixed-link? I don't think it does, because
if multiple link modes are published, it means that it isn't fixed.
As for arguments about the number of lanes, that's a property of the
PHY_INTERFACE_MODE_xxx. There's a long history of this, e.g. MII/RMII
is effectively a very early illustration of reducing the number of
lanes, yet we don't have separate link modes for these.
So, I'm still uneasy about this approach.
--
RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
FTTP is here! 80Mbps down 10Mbps up. Decent connectivity at last!
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