netdev - Re: [PATCH net-next] net: phy: realtek: check validity of 10GbE link-partner advertisement

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Message-ID: <ZwUTDw0oqJ1dvzPq@shell.armlinux.org.uk>
Date: Tue, 8 Oct 2024 12:10:07 +0100
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>,
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH net-next] net: phy: realtek: check validity of 10GbE
 link-partner advertisement

On Fri, Oct 04, 2024 at 11:06:01PM +0100, Daniel Golle wrote:
> On Fri, Oct 04, 2024 at 11:17:28PM +0200, Andrew Lunn wrote:
> > On Fri, Oct 04, 2024 at 04:50:36PM +0100, Daniel Golle wrote:
> > > Only use link-partner advertisement bits for 10GbE modes if they are
> > > actually valid. Check LOCALOK and REMOTEOK bits and clear 10GbE modes
> > > unless both of them are set.
> > > This prevents misinterpreting the stale 2500M link-partner advertisement
> > > bit in case a subsequent linkpartner doesn't do any NBase-T
> > > advertisement at all.
> > > 
> > > Signed-off-by: Daniel Golle <daniel@...rotopia.org>
> > > ---
> > >  drivers/net/phy/realtek.c | 4 ++++
> > >  1 file changed, 4 insertions(+)
> > > 
> > > diff --git a/drivers/net/phy/realtek.c b/drivers/net/phy/realtek.c
> > > index c4d0d93523ad..d276477cf511 100644
> > > --- a/drivers/net/phy/realtek.c
> > > +++ b/drivers/net/phy/realtek.c
> > > @@ -927,6 +927,10 @@ static int rtl822x_read_status(struct phy_device *phydev)
> > >  		if (lpadv < 0)
> > >  			return lpadv;
> > >  
> > > +		if (!(lpadv & MDIO_AN_10GBT_STAT_REMOK) ||
> > > +		    !(lpadv & MDIO_AN_10GBT_STAT_LOCOK))
> > > +			lpadv = 0;
> > > +
> > >  		mii_10gbt_stat_mod_linkmode_lpa_t(phydev->lp_advertising,
> > >  						  lpadv);
> > 
> > I know lpadv is coming from a vendor register, but does
> > MDIO_AN_10GBT_STAT_LOCOK and MDIO_AN_10GBT_STAT_REMOK apply if it was
> > also from the register defined in 802.3? I'm just wondering if this
> > test should be inside mii_10gbt_stat_mod_linkmode_lpa_t()?
> 
> Yes, it does apply and I thought the same, but as
> mii_10gbt_stat_mod_linkmode_lpa_t is used in various places without
> checking those two bits we may break other PHYs which may not use
> them (and apparently this is mostly a problem on RealTek PHYs where
> all the other bits in the register persist in case of a non-NBase-T-
> capable subsequent link-partner after initially being connected to
> an NBase-T-capable one).
> 
> Maybe we could introduce a new function
> mii_10gbt_stat_mod_linkmode_lpa_validate_t()
> which calls mii_10gbt_stat_mod_linkmode_lpa_t() but checks LOCOK and
> REMOK as a precondition?

Isn't the link status supposed to indicate link down of LOCOK
is clear?

Maybe checking these bits should be included in the link status
check, and if not set, then phydev->link should be cleared?

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