netdev - Re: [PATCH net-next v2 1/2] ixgbe: register a mdiobus

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Date:   Mon, 3 Dec 2018 19:18:11 +0100
From:   Andrew Lunn <andrew@...n.ch>
To:     Steve Douthit <stephend@...icom-usa.com>
Cc:     Jeff Kirsher <jeffrey.t.kirsher@...el.com>,
        "David S. Miller" <davem@...emloft.net>,
        "intel-wired-lan@...ts.osuosl.org" <intel-wired-lan@...ts.osuosl.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        Florian Fainelli <f.fainelli@...il.com>
Subject: Re: [PATCH net-next v2 1/2] ixgbe: register a mdiobus

> Agreed, but I'd argue it's the same behavior we have today with the
> existing MII ioctls in this driver.  That's not to say this is good,
> it's just not any less broken than the current state of things.

Agreed.

I actually would be happy with a warning in the commit message that
this code is not sufficient to make use of Linux PHY drivers, because
of the hardware polling. You can then leave fixing that to whoever
needs Linux PHY drivers.

> AFAICT the polling hardware only pokes the device address that the
> driver stores in 'hw->phy.mdio.prtad', so the PHY polling unit would
> never see the switch, if it's even polling at all.  Some of the MAC
> configurations will store MDIO_PRTAD_NONE, in which case I wouldn't
> expect the polling unit to be active.  It's up to the board designer to
> ensure there's no address conflicts on the bus.

Well, the 6390 does use address 0-10 for its port registers, and there
is something which looks like a PHYID in register 3. So for your use
case of DSA, it would be good to ensure it really is disabled.

> Then in the ioctl code, in addition to checking the mii_bus is
> available, also check that the requested address is one that phy_mask
> says mii_bus owns, otherwise we fall through to the old code.

I'm not too bothered with the ioctl. It is there so you can shoot
yourself in the foot. The hardware polling unit just adds more
interesting weapons you can use to shoot yourself in the foot.

    Andrew