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Message-ID: <ZR5/ADvrbMKcKBSy@shell.armlinux.org.uk>
Date: Thu, 5 Oct 2023 10:16:48 +0100
From: "Russell King (Oracle)" <linux@...linux.org.uk>
To: Vladimir Oltean <vladimir.oltean@....com>
Cc: netdev@...r.kernel.org
Subject: Re: What is the purpose of the first phylink_validate() call from
phylink_create()?
On Thu, Oct 05, 2023 at 01:25:23AM +0300, Vladimir Oltean wrote:
> Hi Russell,
>
> In phylink_create() we have this code which populates pl->supported with
> a maximal link mode configuration and then makes a best-effort attempt
> to reduce it to what the physical port actually supports:
>
> diff --git a/drivers/net/phy/phylink.c b/drivers/net/phy/phylink.c
> index 3951e5af8cb5..1e89634ec8ae 100644
> --- a/drivers/net/phy/phylink.c
> +++ b/drivers/net/phy/phylink.c
> @@ -1677,10 +1677,6 @@ struct phylink *phylink_create(struct phylink_config *config,
> __set_bit(PHYLINK_DISABLE_STOPPED, &pl->phylink_disable_state);
> timer_setup(&pl->link_poll, phylink_fixed_poll, 0);
>
> - bitmap_fill(pl->supported, __ETHTOOL_LINK_MODE_MASK_NBITS);
> - linkmode_copy(pl->link_config.advertising, pl->supported);
> - phylink_validate(pl, pl->supported, &pl->link_config);
> -
> ret = phylink_parse_mode(pl, fwnode);
> if (ret < 0) {
> kfree(pl);
>
> However:
>
> - in MLO_AN_FIXED mode, the later call to phylink_parse_fixedlink() will
> overwrite this pl->supported and pl->link_config.advertising with
> another set
>
> - in MLO_AN_INBAND mode, the later call to phylink_parse_mode() will
> also overwrite pl->supported and pl->link_config.advertising
>
> - with a PHY (either in MLO_AN_INBAND or MLO_AN_PHY modes),
> phylink_bringup_phy() will overwrite pl->supported and
> pl->link_config.advertising with stuff from the PHY
>
> Of these 3 cases, phylink_bringup_phy() is the only one which
> potentially does not come immediately after phylink_create().
> So, the effect of the phylink_validate() from phylink_create() will be
> visible only when it's not overwritten, for example when phylink_connect_phy()
> (or one of variants) isn't called at probe time but is delayed until
> ndo_open().
>
> Since mvneta calls phylink_of_phy_connect() from mvneta_open() and I can
> test that, I'm comparing the "ethtool" output produced before running
> "ip link set dev eth0 up", in 2 cases:
>
> - With the phylink_validate() from phylink_create() kept in place:
>
> $ ethtool eth0
> Settings for eth0:
> Supported ports: [ TP AUI MII FIBRE BNC Backplane ]
> Supported link modes: 10baseT/Half 10baseT/Full
> 100baseT/Half 100baseT/Full
> 1000baseT/Full
> 1000baseKX/Full
> 1000baseX/Full
> 100baseT1/Full
> 1000baseT1/Full
> 100baseFX/Half 100baseFX/Full
> 10baseT1L/Full
> 10baseT1S/Full
> 10baseT1S/Half
> 10baseT1S_P2MP/Half
> Supported pause frame use: Symmetric
> Supports auto-negotiation: Yes
> Supported FEC modes: Not reported
> Advertised link modes: Not reported
> Advertised pause frame use: No
> Advertised auto-negotiation: No
> Advertised FEC modes: Not reported
> Speed: Unknown!
> Duplex: Half
> Auto-negotiation: off
> Port: MII
> PHYAD: 0
> Transceiver: internal
> Supports Wake-on: d
> Wake-on: d
> Link detected: no
>
> - And with it removed (the diff from the beginning):
>
> $ ethtool eth0
> Settings for eth0:
> Supported ports: [ ]
> Supported link modes: Not reported
> Supported pause frame use: No
> Supports auto-negotiation: No
> Supported FEC modes: Not reported
> Advertised link modes: Not reported
> Advertised pause frame use: No
> Advertised auto-negotiation: No
> Advertised FEC modes: Not reported
> Speed: Unknown!
> Duplex: Half
> Auto-negotiation: off
> Port: MII
> PHYAD: 0
> Transceiver: internal
> Supports Wake-on: d
> Wake-on: d
> Link detected: no
You've found the exact reason for it - so that we report something that
seems at least reasonable to userspace, rather than reporting absolutely
nothing which may cause issues.
The original code in mvneta would've done this:
int mvneta_ethtool_get_settings(struct net_device *dev, struct ethtool_cmd *cmd)
{
struct mvneta_port *pp = netdev_priv(dev);
if (!pp->phy_dev)
return -ENODEV;
return phy_ethtool_gset(pp->phy_dev, cmd);
}
Thus making the call fail if the device wasn't up - and that may be
an alternative if we're expecting a PHY but we have none.
--
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