netdev - Re: [PATCH net] net: phylink: set phy_state interface when attaching SFP

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Date: Sat, 2 Dec 2023 09:18:42 +0000
From: "Russell King (Oracle)" <linux@...linux.org.uk>
To: Daniel Golle <daniel@...rotopia.org>
Cc: Andrew Lunn <andrew@...n.ch>, Heiner Kallweit <hkallweit1@...il.com>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	Marek Behún <kabel@...nel.org>,
	Pali Rohár <pali@...nel.org>,
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
	Eric Woudstra <ericwouds@...il.com>,
	John Crispin <john@...ozen.org>
Subject: Re: [PATCH net] net: phylink: set phy_state interface when attaching
 SFP

On Fri, Dec 01, 2023 at 06:19:20PM +0000, Daniel Golle wrote:
> On Sat, Nov 25, 2023 at 08:28:20AM +0000, Russell King (Oracle) wrote:
> > On Sat, Nov 25, 2023 at 04:56:20AM +0000, Daniel Golle wrote:
> > > Assume 'usxgmii' being set as initial interface mode in DTS. Now plug
> > > a 2.5GBase-T SFP module with exposed PHY. Currently this results in
> > > a rather bizare situation:
> > > 
> > > RTL8221B-VB-CG 2.5Gbps PHY (C45) i2c:sfp1-wan:11: rtl822x_c45_get_features: supported=00,00000000,00008000,000080ef
> > > mtk_soc_eth 15100000.ethernet eth2: requesting link mode phy/2500base-x with support 00,00000000,00008000,0000e0ef
> > > mtk_soc_eth 15100000.ethernet eth2: switched to phy/2500base-x link mode   <<< !!!!!!
> > > mtk_soc_eth 15100000.ethernet eth2: major config usxgmii    <<< !!!!!!
> > > mtk_soc_eth 15100000.ethernet eth2: phylink_mac_config: mode=phy/usxgmii/none adv=00,00000000,00000000,00000000 pause=00
> > > mtk_soc_eth 15100000.ethernet eth2: PHY [i2c:sfp1-wan:11] driver [RTL8221B-VB-CG 2.5Gbps PHY (C45)] (irq=POLL)
> > > mtk_soc_eth 15100000.ethernet eth2: phy: 2500base-x setting supported 00,00000000,00008000,0000e0ef advertising 00,00000000,00008000,0000e0ef
> > > 
> > > Then the link seemingly comes up (but is dead) because no subsequent
> > > call to phylink_major_config actually configured MAC and PCS for
> > > 2500base-x mode.
> > > 
> > > This is because phylink_mac_initial_config() considers
> > > pl->phy_state.interface if in MLO_AN_PHY mode while
> > > phylink_sfp_set_config() only sets pl->link_config.interface.
> > > 
> > > Also set pl->phy_state.interface in phylink_sfp_set_config().
> > 
> > Does it _actually_ matter?
> 
> It does matter, I'm suggesting this change because the SFP module
> won't work without it.
> 
> > When the PHY's link comes up, doesn't it get sorted out for the real
> > mode that will be used?
> 
> That does happen once the interface mode *changes* to anything else,
> than 2500M/Full and the PHY driver sets state->interface to SGMII.
> However, initially it does *not* happen, probably because phylink
> ends up believing MAC and PCS are already operating in 2500base-x
> mode (but that's not the case).
> 
> Previously (eg. with the BananaPi R3) this has not been a problem
> because the default interface mode defined in device tree anyway has
> also been 2500base-x. Now that I'm testing the same module with the
> R4 which uses usxgmii by default the problem surfaced.

Okay, I think what we have here is an ordering issue in
phylink_sfp_connect_phy(). phylink_bringup_phy() will set
phy_state.interface, but that happens after the major config has
happened.

With a built-in PHY, the sequence would be:

 - connect to PHY (which calls phylink_bringup_phy())
 - phylink_start() (which calls phylink_major_config())

whereas in this case we have the reverse. That needs to be sorted.
I can't do that over this weekend, but if you remind me I'll look
at it next week.

Thanks.

-- 
RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
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