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

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Message-ID: <20190224153125.f2n3xfjyjswd7ioa@shell.armlinux.org.uk>
Date:   Sun, 24 Feb 2019 15:31:26 +0000
From:   Russell King - ARM Linux admin <linux@...linux.org.uk>
To:     Andrew Lunn <andrew@...n.ch>
Cc:     Heiner Kallweit <hkallweit1@...il.com>,
        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 12:42:35AM +0100, Andrew Lunn wrote:
> Looking forward, at some point we are going to have to make fixed-link
> support higher speeds. That probably means we need a swphy-c45 which
> emulates the standard registers for 2.5G, 5G and 10G. At that point
> genphy will not work...

Do we _need_ to emulate Clause 45 PHYs?  Today, the MII interface does
not work with Clause 45 PHYs, so there is no userspace accessing these
PHYs out there.  I have a patch that adds support for the MII ioctls
which gives me the ability to poke around in the 88x3310 for
investigatory / debug purposes.

However, I don't see the point of adding what would be very complex
Clause 45 support (we'd have to emulate the PMA/PMD, PCS and AN as a
minimum) when we have the ethtool API, and then we have the issue
that not all advertisement modes are standardised in Clause 45 -
there are some missing.

As I understand it, the swphy for fixed-links only exists because we
have existing tooling that expects Clause 22 PHYs to exist.  This will
break even if we were to add Clause 45 support as many bits in the
first 16 registers have different meanings.

-- 
RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
FTTC broadband for 0.8mile line in suburbia: sync at 12.1Mbps down 622kbps up
According to speedtest.net: 11.9Mbps down 500kbps up