netdev - Re: No traffic with Marvell switch and latest linux-next

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Date:   Sun, 24 Feb 2019 15:34:49 +0000
From:   Russell King - ARM Linux admin <linux@...linux.org.uk>
To:     Heiner Kallweit <hkallweit1@...il.com>
Cc:     Andrew Lunn <andrew@...n.ch>,
        Florian Fainelli <f.fainelli@...il.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: No traffic with Marvell switch and latest linux-next

On Sun, Feb 24, 2019 at 04:28:32PM +0100, Heiner Kallweit wrote:
> On 24.02.2019 16:15, Russell King - ARM Linux admin wrote:
> > On Sun, Feb 24, 2019 at 04:04:03PM +0100, Andrew Lunn wrote:
> >>> I think what's not correct is that phydev->autoneg is set
> >>> (by phy_device_create) for a fixed link.
> >>
> >> Fixed-link tries to emulate auto-neg:
> >>
> >>                 bmsr |= BMSR_LSTATUS | BMSR_ANEGCOMPLETE;
> >>
> >> Maybe it needs better emulation of auto-neg?
> > 
> > Or maybe it needs to represent a fixed-speed PHY by clearing bit 1.3
> > (BMSR_ANEGCAPABLE).  In any case, 0.12 (BMCR_ANENABLE) is not set,
> > so according to 802.3-2015, we should not be setting 1.5
> > (BMSR_ANEGCOMPLETE).
> > 
> > However, swphy does try to emulate autonegotiation - we do have cases
> > where swphy is used in situations where the speed and duplex are not
> > fixed.  It returns an emulated link partner advertisement for the
> > current speed, which would suggest that we should set BMCR_ANENABLE.
> > 
> If we emulate auto-neg, then it's not needed to set the speed bits
> in BMCR. Also what just comes to my mind, certain speeds like 1000BaseT
> don't support forced mode. So we may have to go with auto-neg.

Sure.

> To avoid the original issue it should be sufficient to copy
> supported -> advertising at a suited place.

Why bother - the software PHY emulation is an emulation to allow
existing userspace that pre-dates the ethtool API to get some link
parameters.  If we augment the PHY emulation in non-standard ways,
userspace will need to be updated to handle those non-standard
ways.  If userspace needs to be updated, why not just bite the
bullet and update to ethtool APIs rather than adding more
complication through an emulation layer?

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