linux-kernel - Re: [PATCH] net: phy: marvell: Fix pause frame negotiation

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Date:   Sat, 11 Apr 2020 15:24:01 +0200
From:   Clemens Gruber <clemens.gruber@...ruber.com>
To:     Russell King - ARM Linux admin <linux@...linux.org.uk>
Cc:     Jakub Kicinski <kuba@...nel.org>, netdev@...r.kernel.org,
        Andrew Lunn <andrew@...n.ch>,
        Florian Fainelli <f.fainelli@...il.com>,
        Heiner Kallweit <hkallweit1@...il.com>,
        "David S . Miller" <davem@...emloft.net>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] net: phy: marvell: Fix pause frame negotiation

On Sat, Apr 11, 2020 at 10:17:05AM +0100, Russell King - ARM Linux admin wrote:
> On Fri, Apr 10, 2020 at 05:43:04PM -0700, Jakub Kicinski wrote:
> > On Wed,  8 Apr 2020 23:43:26 +0200 Clemens Gruber wrote:
> > > The negotiation of flow control / pause frame modes was broken since
> > > commit fcf1f59afc67 ("net: phy: marvell: rearrange to use
> > > genphy_read_lpa()") moved the setting of phydev->duplex below the
> > > phy_resolve_aneg_pause call. Due to a check of DUPLEX_FULL in that
> > > function, phydev->pause was no longer set.
> > > 
> > > Fix it by moving the parsing of the status variable before the blocks
> > > dealing with the pause frames.
> > > 
> > > Fixes: fcf1f59afc67 ("net: phy: marvell: rearrange to use genphy_read_lpa()")
> > > Cc: stable@...r.kernel.org # v5.6+
> > 
> > nit: please don't CC stable on networking patches
> > 
> > > Signed-off-by: Clemens Gruber <clemens.gruber@...ruber.com>
> > > ---
> > >  drivers/net/phy/marvell.c | 44 +++++++++++++++++++--------------------
> > >  1 file changed, 22 insertions(+), 22 deletions(-)
> > > 
> > > diff --git a/drivers/net/phy/marvell.c b/drivers/net/phy/marvell.c
> > > index 4714ca0e0d4b..02cde4c0668c 100644
> > > --- a/drivers/net/phy/marvell.c
> > > +++ b/drivers/net/phy/marvell.c
> > > @@ -1263,6 +1263,28 @@ static int marvell_read_status_page_an(struct phy_device *phydev,
> > >  	int lpa;
> > >  	int err;
> > >  
> > > +	if (!(status & MII_M1011_PHY_STATUS_RESOLVED))
> > > +		return 0;
> > 
> > If we return early here won't we miss updating the advertising bits?
> > We will no longer call e.g. fiber_lpa_mod_linkmode_lpa_t().
> > 
> > Perhaps extracting info from status should be moved to a helper so we
> > can return early without affecting the rest of the flow?
> > 
> > Is my understanding correct?  Russell?
> 
> You are correct - and yes, there is also a problem here.
> 
> It is not clear whether the resolved bit is set before or after the
> link status reports that link is up - however, the resolved bit
> indicates whether the speed and duplex are valid.

I assumed that in the fiber case, the link status register won't be 1
until autonegotiation is complete. There is a part in the 88E1510
datasheet on page 57 [2.6.2], which says so but it's in the Fiber/Copper
Auto-Selection chapter and I am not sure if that's true in general. (?)
(For copper, we call genphy_update_link, which sets phydev->link to 0 if
autoneg is enabled && !completed. And according to the datasheet,
the resolved bit is set when autonegotiation is completed || disabled)

TL/DR:
It's probably a good idea to force link to 0 to be sure, as you
suggested below. I will send a v2 with that change.

Moving the extraction of info to a helper is probably better left to a
separate patch?

> What I've done elsewhere is if the resolved bit is not set, then we
> force phydev->link to be false, so we don't attempt to process a
> link-up status until we can read the link parameters.  I think that's
> what needs to happen here, i.o.w.:
> 
> 	if (!(status & MII_M1011_PHY_STATUS_RESOLVED)) {
> 		phydev->link = 0;
> 		return 0;
> 	}
> 
> especially as we're not reading the LPA.

Thanks,
Clemens