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

[Russell King - ARM Linux admin <linux@armlinux.org.uk>]

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@vger.kernel.org # v5.6+
> 
> nit: please don't CC stable on networking patches
> 
> > Signed-off-by: Clemens Gruber <clemens.gruber@pqgruber.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.

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.

-- 
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