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

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Message-ID: <20200412170336.GA1826@workstation.tuxnet>
Date:   Sun, 12 Apr 2020 19:03:36 +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 02:43:44PM +0100, Russell King - ARM Linux admin wrote:
> The fiber code is IMHO very suspect; the decoding of the pause status
> seems to be completely broken. However, I'm not sure whether anyone
> actually uses that or not, so I've been trying not to touch it.

If the following table for the link partner advertisement is correct..
PAUSE           ASYM_PAUSE      MEANING
0               0               Link partner has no pause frame support
0               1               <-  Link partner can TX pause frames
1               0               <-> Link partner can RX and TX pauses
1               1                -> Link partner can RX pause frames

..then I think both pause and asym_pause have to be assigned
independently, like this:
phydev->pause = !!(lpa & LPA_1000XPAUSE);
phydev->asym_pause = !!(lpa & LPA_1000XPAUSE_ASYM);

(Using the defines from uapi mii.h instead of the redundant/combined
LPA_PAUSE_FIBER etc. which can then be removed from marvell.c)

Currently, if LPA_1000XPAUSE_ASYM is set we do pause=1 and asym_pause=1
no matter if LPA_1000XPAUSE is set. This could lead us to mistake a link
partner who can only send for one who can only receive pause frames.
^ Was this the problem you meant?

I saw that for the copper case and in other drivers, we first set the
ETHTOOL_LINK_MODE_(Asym_)Pause_BIT bit in lp_advertising and then set
phydev->(asym_)pause depending on the ETHTOOL_LINK_MODE_... bit.
Do you agree that we should also set the ETHTOOL_ bits in the fiber
case?

Does anybody have access to a Marvell PHY with 1000base-X Ethernet?
(I only have a 88E1510 + 1000Base-T at the home office)

Thanks,
Clemens