Subject: Re: [PATCH RFC net-next] net: phylink: always config mac for (delayed) phy

From: Daniel Golle <[email-masked]>
Date: Tue, 7 Jan 2025 13:16:33 +0000

On Tue, Jan 07, 2025 at 12:47:14PM +0000, Russell King (Oracle) wrote:
> Going through the log...
> 
> On Tue, Jan 07, 2025 at 01:36:15PM +0100, Eric Woudstra wrote:
> > Log before this patch is applied:
> > [root@bpir3 ~]# dmesg | grep eth1
> > [    2.515179] mtk_soc_eth 15100000.ethernet eth1: mediatek frame engine at 0xffff800082380000, irq 123
> > [   38.271431] mtk_soc_eth 15100000.ethernet eth1: configuring for inband/2500base-x link mode
> > [   38.279828] mtk_soc_eth 15100000.ethernet eth1: major config, requested inband/2500base-x
> > [   38.288009] mtk_soc_eth 15100000.ethernet eth1: interface 2500base-x inband modes: pcs=01 phy=00
> > [   38.296800] mtk_soc_eth 15100000.ethernet eth1: major config, active inband/inband,an-disabled/2500base-x
> 
> This is indeed without the PHY. We're using inband, although the PCS
> mode is PHYLINK_PCS_NEG_INBAND_DISABLED, meaning inband won't be
> used. As there is no PHY, we can't switch to MLO_AN_PHY.
> 
> > [   38.306362] mtk_soc_eth 15100000.ethernet eth1: phylink_mac_config: mode=inband/2500base-x/none adv=00,00000000,00008000,0000e240 pause=04
> > [   39.220149] mtk_soc_eth 15100000.ethernet eth1:  interface 2 (mii) rate match none supports 0-3,6-7,13-14
> > [   39.229758] mtk_soc_eth 15100000.ethernet eth1:  interface 3 (gmii) rate match none supports 0-3,5-7,13-14
> > [   39.239420] mtk_soc_eth 15100000.ethernet eth1:  interface 4 (sgmii) rate match none supports 0-3,5-7,13-14
> > [   39.249173] mtk_soc_eth 15100000.ethernet eth1:  interface 22 (1000base-x) rate match none supports 5-7,13-14
> > [   39.259080] mtk_soc_eth 15100000.ethernet eth1:  interface 23 (2500base-x) rate match none supports 6-7,13-14,47
> > [   39.594676] mtk_soc_eth 15100000.ethernet eth1: PHY i2c:sfp-1:11 uses interfaces 4,23, validating 4,23
> 
> The PHY comes along...
> 
> > [   39.603992] mtk_soc_eth 15100000.ethernet eth1:  interface 4 (sgmii) rate match none supports 0-3,5-7,13-14
> > [   39.650080] mtk_soc_eth 15100000.ethernet eth1:  interface 23 (2500base-x) rate match none supports 6-7,13-14,47
> > [   39.660266] mtk_soc_eth 15100000.ethernet eth1: PHY [i2c:sfp-1:11] driver [RTL8221B-VB-CG 2.5Gbps PHY (C45)] (irq=POLL)
> > [   39.671037] mtk_soc_eth 15100000.ethernet eth1: phy: 2500base-x setting supported 00,00000000,00008000,000060ef advertising 00,00000000,00008000,000060ef
> > [   39.684761] mtk_soc_eth 15100000.ethernet eth1: requesting link mode inband/2500base-x with support 00,00000000,00008000,000060ef
> 
> We decide to use MLO_AN_INBAND and 2500base-X, which we're already using.
> 
> > [   40.380076] mtk_soc_eth 15100000.ethernet eth1: phy link down 2500base-x/Unknown/Unknown/none/off
> > [   40.397090] brlan: port 5(eth1) entered blocking state
> > [   40.402223] brlan: port 5(eth1) entered disabled state
> > [   40.407437] mtk_soc_eth 15100000.ethernet eth1: entered allmulticast mode
> > [   40.414400] mtk_soc_eth 15100000.ethernet eth1: entered promiscuous mode
> > [   44.500077] mtk_soc_eth 15100000.ethernet eth1: phy link up 2500base-x/2.5Gbps/Full/none/off
> > [   44.508528] mtk_soc_eth 15100000.ethernet eth1: No phy led trigger registered for speed(2500)
> 
> ... but we don't see link-up reported by the PCS after the PHY comes
> up. Why is that - I think that needs investigation before we proceed
> to patch the issue, because that suggests the PCS isn't seeing
> valid 2500base-X from the PHY.

The PCS doesn't support in-band status in 2500Base-X mode, or at least
the implementation isn't compatible with those RealTek PHYs.

In OpenWrt we carry a downstream patch to disable in-band status on the
side of the PHY which fixes the issue:

https://git.openwrt.org/?p=openwrt/openwrt.git;a=blob;f=target/linux/generic/pending-6.6/720-02-net-phy-realtek-disable-SGMII-in-band-AN-for-2-5G-PHYs.patch;h=7e48c16515db8e401495dc1c505319424773ee11;hb=HEAD