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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. -- 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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